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| [[Image:Magnetocaloric effect1 04a.svg|thumb|400px|Gadolinium alloy heats up inside the magnetic field and loses thermal energy to the environment, so it exits the field cooler than when it entered.]]
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| '''Magnetic refrigeration''' is a cooling technology based on the '''magnetocaloric effect'''. This technique can be used to attain extremely low [[temperature]]s, as well as the ranges used in common [[refrigerator]]s, depending on the design of the system.
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| The effect was first observed by the German physicist [[Emil Warburg]] (1881) and the fundamental principle was suggested by [[Peter Debye|Debye]] (1926) and [[William Giauque|Giauque]] (1927).<ref>{{cite book | last = Zemansky | first = Mark W. | title = Temperatures very low and very high | publisher = Dover | year = 1981 | location = New York | page = 50 | isbn = 0-486-24072-X }}</ref> The first working magnetic refrigerators were constructed by several groups beginning in 1933. Magnetic refrigeration was the first method developed for cooling below about 0.3K (a temperature attainable by [[Helium-3|<sup>3</sup>He]] refrigeration, that is pumping on the <sup>3</sup>He vapors).
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| ==The magnetocaloric effect==
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| The magnetocaloric effect (MCE, from ''[[magnet]]'' and ''[[calorie]]'') is a magneto-[[thermodynamic]] phenomenon in which a change in temperature of a suitable material is caused by exposing the material to a changing magnetic field. This is also known by low temperature physicists as ''[[Adiabatic process|adiabatic]] demagnetization'', due to the application of the process specifically to create a temperature drop. In that part of the overall refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a chosen (magnetocaloric) material to become disoriented from the magnetic field by the agitating action of the thermal energy ([[phonon]]s) present in the material. If the material is isolated so that no energy is allowed to (re)migrate into the material during this time, ''i.e.'', an adiabatic process, the [[temperature]] drops as the domains absorb the thermal energy to perform their reorientation. The randomization of the domains occurs in a similar fashion to the randomization at the [[curie temperature]] of a ferromagnetic material, except that magnetic dipoles overcome a decreasing external magnetic field while energy remains constant, instead of magnetic domains being disrupted from internal [[ferromagnetism]] as energy is added.
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| One of the most notable examples of the magnetocaloric effect is in the chemical element [[gadolinium]] and some of its [[alloys]]. Gadolinium's temperature is observed to increase when it enters certain magnetic fields. When it leaves the magnetic field, the temperature drops. The effect is considerably stronger for the gadolinium [[alloy]] [[Gadolinium|Gd]]<sub>5</sub>([[Silicon|Si]]<sub>2</sub>[[Germanium|Ge]]<sub>2</sub>).<ref name="Ames">{{cite web | author = Karl Gschneidner, Jr. and Kerry Gibson | title = Magnetic Refrigerator Successfully Tested | work = Ames Laboratory News Release | publisher = Ames Laboratory |date= December 7, 2001 | url = http://www.external.ameslab.gov/news/release/01magneticrefrig.htm | accessdate = 2006-12-17 }}</ref> [[Praseodymium]] alloyed with [[nickel]] ([[Praseodymium|Pr]][[Nickel|Ni]]<sub>5</sub>) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of [[absolute zero]].<ref>{{cite book | last = Emsley | first = John| title = Nature's Building Blocks | publisher = [[Oxford University Press]] |year= 2001 | page = 342 | isbn = 0-19-850341-5 }}</ref>
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| ===Equation===
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| The magnetocaloric effect can be quantified with the equation below:
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| <math>\Delta T_{ad}=-\int_{H_0}^{H_1}\Bigg(\frac {T}{C(T,H)}\Bigg)_H{\Bigg(\frac {\partial M(T,H)}{\partial T}\Bigg)}_H dH</math>
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| T is the temperature, H is the applied magnetic field, C is the heat capacity of the working magnet (refrigerant), and M is the magnetization of the refrigerant.
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| From the equation we can see that magnetocaloric effect can be enhanced by:
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| *applying a large field
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| *using a magnet with a small heat capacity
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| *using a magnet with a large change in magnetization vs temperature, at a constant magnetic field
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| === Thermodynamic cycle === | |
| [[Image:MCE.gif|right|thumb|400px|Analogy between magnetic refrigeration and vapor cycle or conventional refrigeration. ''H'' = externally applied magnetic field; ''Q'' = heat quantity; ''P'' = pressure; Δ''T''<sub>ad</sub> = adiabatic temperature variation]]
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| The cycle is performed as a [[refrigeration cycle]], analogous to the [[Carnot cycle]], and can be described at a starting point whereby the chosen working substance is introduced into a [[magnetic field]], ''i.e.'', the magnetic flux density is increased. The working material is the refrigerant, and starts in thermal equilibrium with the refrigerated environment.
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| #''Adiabatic magnetization:'' A magnetocaloric substance is placed in an insulated environment. The increasing external magnetic field (+''H'') causes the [[magnetic dipole]]s of the atoms to align, thereby decreasing the material's magnetic [[entropy]] and [[heat capacity]]. Since overall energy is not lost (yet) and therefore total [[entropy]] is not reduced (according to thermodynamic laws), the net result is that the item heats up (''T'' + Δ''T''<sub>ad</sub>).
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| #''Isomagnetic enthalpic transfer:'' This added heat can then be removed (-''Q'') by a fluid or gas — gaseous or liquid [[helium]], for example. The magnetic field is held constant to prevent the dipoles from reabsorbing the heat. Once sufficiently cooled, the magnetocaloric substance and the coolant are separated (''H''=0).
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| #''Adiabatic demagnetization:'' The substance is returned to another adiabatic (insulated) condition so the total entropy remains constant. However, this time the magnetic field is decreased, the thermal energy causes the magnetic moments to overcome the field, and thus the sample cools, ''i.e.'', an adiabatic temperature change. Energy (and entropy) transfers from thermal entropy to magnetic entropy (disorder of the magnetic dipoles).
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| #''Isomagnetic entropic transfer:'' The magnetic field is held constant to prevent the material from heating back up. The material is placed in thermal contact with the environment being refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+''Q'').
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| Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle begins again.
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| ===Applied technique===
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| The basic operating principle of an adiabatic demagnetization refrigerator (ADR) is the use of a strong [[magnetic field]] to control the [[entropy]] of a sample of material, often called the "refrigerant". Magnetic field constrains the orientation of magnetic [[dipole]]s in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, and this corresponds to lower [[entropy]] and [[specific heat capacity|heat capacity]] because the material has (effectively) lost some of its internal [[degrees of freedom (physics and chemistry)|degrees of freedom]]. If the refrigerant is kept at a constant temperature through thermal contact with a [[heat]] sink (usually liquid [[helium]]) while the magnetic field is switched on, the refrigerant must lose some [[energy]] because it is [[thermodynamic equilibrium|equilibrated]] with the heat sink. When the magnetic field is subsequently switched off, the heat capacity of the refrigerant rises again because the degrees of freedom associated with orientation of the dipoles are once again liberated, pulling their share of [[equipartition of energy|equipartitioned]] energy from the [[kinetic energy|motion]] of the [[molecule]]s, thereby lowering the overall temperature of a [[system]] with decreased energy. Since the system is now [[Thermal insulation|insulated]] when the magnetic field is switched off, the process is [[adiabatic]], ''i.e.'', the system can no longer exchange energy with its surroundings (the heat sink), and its temperature decreases below its initial value, that of the heat sink.
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| The operation of a standard ADR proceeds roughly as follows. First, a strong magnetic field is applied to the refrigerant, forcing its various magnetic dipoles to align and putting these degrees of freedom of the refrigerant into a state of lowered entropy. The heat sink then absorbs the heat released by the refrigerant due to its loss of entropy. Thermal contact with the heat sink is then broken so that the system is insulated, and the magnetic field is switched off, increasing the heat capacity of the refrigerant, thus decreasing its temperature below the temperature of the helium heat sink. In practice, the magnetic field is decreased slowly in order to provide continuous cooling and keep the sample at an approximately constant low temperature. Once the field falls to zero or to some low limiting value determined by the properties of the refrigerant, the cooling power of the ADR vanishes, and heat leaks will cause the refrigerant to warm up.
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| ==Working materials==
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| The magnetocaloric effect is an intrinsic property of a magnetic solid. This thermal response of a solid to the application or removal of magnetic fields is maximized when the solid is near its magnetic ordering temperature.
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| The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic order process: the magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems; it can be substantial for normal ferromagnets which undergo a second order magnetic transition; and it is generally the largest for a ferromagnet which undergoes a first order magnetic transition.
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| Also, crystalline electric fields and pressure can have a substantial influence on magnetic entropy and adiabatic temperature changes.
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| Currently, [[alloys]] of [[gadolinium]] producing {{nowrap|3 - 4 K}} per [[tesla (unit)|tesla]] [K/T] of change in a magnetic field can be used for magnetic refrigeration.
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| Recent research on materials that exhibit a giant entropy change showed that Gd<sub>5</sub>(Si<sub>''x''</sub>Ge<sub>1−''x''</sub>)<sub>4</sub>, La(Fe<sub>''x''</sub>Si<sub>1−''x''</sub>)<sub>13</sub>H<sub>''x''</sub> and MnFeP<sub>1−''x''</sub>As<sub>''x''</sub> alloys, for example, are some of the most promising substitutes for gadolinium and its alloys — GdDy, GdTb, etc. These materials are called giant magnetocaloric effect (GMCE) materials.
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| Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature since they undergo second-order phase transitions which have no magnetic or thermal hysteresis involved. However, moving away from rare earth metals and towards other materials including MnFeP1−xAsx has distinct cost and scarcity advantages. The development of this technology is very materials dependent and will likely not be able to replace vapor-compression refrigeration without significantly improved materials that are cheap, abundant, and exhibit much larger magnetocaloric effects over a larger range of temperatures. Ultimately, these materials will also need to undergo significant temperature changes with a field around two tesla or less so that permanent magnets can be used for the production of the magnetic field [29, 30].
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| ===Paramagnetic salts===
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| The originally suggested refrigerant was a [[paramagnetism|paramagnetic]] [[salt]], such as [[cerium]] [[magnesium]] [[nitrate]]. The active [[magnetic field|magnetic]] [[dipole]]s in this case are those of the [[electron shell]]s of the paramagnetic atoms.
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| In a paramagnetic salt ADR, the heat sink is usually provided by a pumped <sup>4</sup>He (about 1.2 K) or <sup>3</sup>He (about 0.3 K) [[cryostat]]. An easily attainable 1 T magnetic field is generally required for the initial magnetization. The minimum temperature attainable is determined by the self-magnetization tendencies of the chosen refrigerant salt, but temperatures from 1 to 100 mK are accessible. [[Dilution refrigerator]]s had for many years supplanted paramagnetic salt ADRs, but interest in space-based and simple to use lab-ADRs has remained, due to the complexity and unreliability of the dilution refrigerator
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| Eventually paramagnetic salts become either [[diamagnetism|diamagnetic]] or [[ferromagnetism|ferromagnetic]], limiting the lowest temperature which can be reached using this method.
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| ===Nuclear demagnetization===
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| One variant of adiabatic demagnetization that continues to find substantial research application is nuclear demagnetization refrigeration (NDR). NDR follows the same principle described above, but in this case the cooling power arises from the [[spin (physics)#Spin and magnetic moment|magnetic dipoles of the nuclei]] of the refrigerant atoms, rather than their electron configurations. Since these dipoles are of much smaller magnitude, they are less prone to self-alignment and have lower intrinsic minimum fields. This allows NDR to cool the nuclear spin system to very low temperatures, often 1 µK or below. Unfortunately, the small magnitudes of nuclear magnetic dipoles also makes them less inclined to align to external fields. Magnetic fields of 3 teslas or greater are often needed for the initial magnetization step of NDR.
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| In NDR systems, the initial heat sink must sit at very low temperatures (10–100 mK). This precooling is often provided by the mixing chamber of a [[dilution refrigerator]] or a paramagnetic salt.
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| ==Commercial development==
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| This refrigeration technology, has not proven viable by the end of 2013 for mass commercial applications (only for some ultra low cryogenic applications - but this has been for the last 50 years). If it can be proven to be competitive and cost effective and environmental friendly then it could be used in any possible application where cooling, heating or power generation is used today. Since it is only at an early stage of development, there are several technical and efficiency issues that should be analyzed. The magnetocaloric refrigeration system is composed of pumps, electric motors, secondary fluids, heat exchangers of different types, magnets and magnetic materials. These processes are greatly affected by irreversibilities and should be adequately considered.
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| At the end of 2013, Cooltech <ref>http://www.cooltech-applications.com/</ref> Applications announced that its first refrigeration equipment should be placed on the professional market for 2014.
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| Appliances using this method could have a smaller [[Environmental impact assessment|environmental impact]] if the method is perfected and replaces [[Haloalkane|hydrofluorocarbon (HFCs)]] refrigerators (some refrigerators still use [[Haloalkane|HCFCs]] which have considerable effect on the ozone layer. At present, however, the superconducting magnets that are used in the process have to themselves be cooled down to the temperature of [[liquid nitrogen]], or with even colder, and relatively expensive, liquid [[helium]]. Considering these fluids have boiling points of 77.36 K and 4.22 K respectively, the technology is clearly not cost- and energy-efficient for home appliances, but for experimental, laboratory, and industrial use only.
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| Recent research on materials that exhibit a large entropy change showed that alloys are some of the most promising substitutes of gadolinium and its alloys — GdDy, GdTb, etc. Gadolinium and its alloys are the best material available today for magnetic refrigeration near room temperature. There are still some thermal and magnetic [[hysteresis]] problems to be solved for them to become truly useful [V. Provenzano, A.J. Shapiro, and R.D. Shull, ''Nature'' 429, 853 (2004)] and scientists are working hard to achieve this goal. Thermal hysteresis problems is solved therefore in adding ferrite (5:4).{{Citation needed|date=July 2008}}
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| Research and a demonstration proof of concept in 2001 succeeded in applying commercial-grade materials and permanent magnets at room temperatures to construct a magnetocaloric refrigerator which promises wide use.<ref name = "Ames Lab-2001">{{cite news | url=http://www.ameslab.gov/news/ins01-11Magnetic.htm | last = Gibson | first = Kerry | work = INSIDER Newsletter for employees of Ames Laboratory | title = Magnetic Refrigerator Successfully Tested: Ames Laboratory developments help push boundaries of new refrigeration technology |date = November 2001}}(Vol. 112, No.10 )</ref>
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| This technique has been used for many years in [[cryogenics|cryogenic]] systems for producing further cooling in systems already cooled to temperatures of 4 K and lower.
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| On August 20, 2007, the [[Risø National Laboratory]] (Denmark) at the [[Technical University of Denmark]], claimed to have reached a milestone in their magnetic cooling research when they reported a temperature span of 8.7 K.<ref>[http://www.risoe.dk/News_archives/News/2007/0820_magnetisk_koeling.aspx Milestone in magnetic cooling, Risø News, August 20, 2007]. Retrieved August 28, 2007.</ref> They hope to introduce the first commercial applications of the technology by 2010.
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| Cooltech <ref>http://www.cooltech-applications.com/</ref> has been trying to commercialize this technology since 2011. At the end of 2013, a production line was completed with a capacity of 10,000 units /year and the first assembled products.
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| The best way to figure out if a technology is a bogus or not is to measure the real efficiency in real conditions, trusting companies or peoples power point presentations can lead to big losses.
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| ===Current and future uses===
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| There are still some thermal and magnetic [[hysteresis]] problems to be solved for these first-order phase transition materials that exhibit the GMCE to become really useful; this is a subject of current research. A useful review on magnetocaloric materials published in 2005 is entitled "Recent developments in magnetocaloric materials" by Dr. Karl A. Gschneidner, et al.<ref>
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| Gschneidner, Karl A., Jr.; Pecharsky, V. K. and Tsokol1, A.O.
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| [http://www.iop.org/EJ/abstract/0034-4885/68/6/R04/ Recent developments in magnetocaloric materials] | |
| ''Report on Progress in Physics.'' (2005) Volume 68, pages 1479–1539.
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| </ref>
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| This effect is currently being explored to produce better refrigeration techniques, especially for use in [[spacecraft]]. This technique is already used to achieve cryogenic temperatures in the laboratory setting (below 10K). As an object displaying MCE is moved into a magnetic field, the magnetic spins align, lowering the entropy. Moving that object out of the field allows the object to increase its entropy by absorbing heat from the environment and disordering the spins. In this way, heat can be taken from one area to another. Should materials be found to display this effect near room temperature, refrigeration without the need for compression may be possible, increasing energy efficiency.
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| The use of this technology to replace larger [[vapor-compression refrigeration]] units, which typically achieve performance coefficients of 60% of that of a theoretical ideal Carnot cycle is unlikely in the near term.
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| Small domestic refrigerators are however much less efficient. <ref>{{cite web|url=http://www.osti.gov/bridge/purl.cover.jsp?purl=/40784-UgOxYh/webviewable/40784.pdf |title=Information Bridge: DOE Scientific and Technical Information - Sponsored by OSTI |publisher=Osti.gov |date=2012-08-31 |accessdate=2012-10-04}}</ref>
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| This technology could eventually compete with other cryogenic heat pumps for gas liquefaction purposes.
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| Gschneidner stated in 1999 that: "large-scale applications using magnetic refrigeration, such as commercial air conditioning and supermarket refrigeration systems, could be available within 5–10 years. Within 10–15 years, the technology could be available in home refrigerators and air conditioners."<ref>[http://www.ameslab.gov/final/News/1999rel/99crada.html ]{{dead link|date=October 2012}}</ref>
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| == History ==
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| The effect was discovered in pure [[iron]] in 1881 by German physicist [[Emil Warburg]]. Originally, the cooling effect varied between 0.5 to 2 K/T.
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| Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by two scientists, Peter Debye in 1926 and William Giauque in 1927.
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| This cooling technology was first demonstrated experimentally by chemist Nobel Laureate [[William F. Giauque]] and his colleague [[D. P. MacDougall]] in 1933 for cryogenic purposes when they reached 0.25 K.<ref>{{cite journal |last=Giauque |first=W. F. |last2=MacDougall |first2=D. P. |year=1933 |title=Attainment of Temperatures Below 1° Absolute by Demagnetization of Gd<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>·8H<sub>2</sub>O |journal=Phys. Rev. |volume=43 |issue=9 |page=768 |doi=10.1103/PhysRev.43.768 |bibcode = 1933PhRv...43..768G }}</ref> Between 1933 and 1997, a number of advances in utilization of the MCE for cooling occurred.<ref>{{cite book |last=Gschneidner |first=K. A. Jr. |last2=Pecharsky |first2=V. K. |year=1997 |chapter= |title=Rare Earths: Science, Technology and Applications III |editor-first=R. G. |editor-last=Bautista |editor2-last=''et al.'' |location=Warrendale, PA |publisher=The Minerals, Metals and Materials Society |page=209 |isbn= }}</ref><ref>{{cite journal |last=Pecharsky |first=V. K. |last2=Gschneidner |first2=K. A. Jr. |year=1999 |title=Magnetocaloric Effect and Magnetic Refrigeration |journal=J. Magn. Magn. Mater. |volume=200 |issue=1–3 |pages=44–56 |doi=10.1016/S0304-8853(99)00397-2 |bibcode = 1999JMMM..200...44P }}</ref><ref>{{cite journal |last=Gschneidner |first=K. A. Jr. |last2=Pecharsky |first2=V. K. |year=2000 |title=Magnetocaloric Materials |journal=Annu. Rev. Mater. Sci. |volume=30 |issue=1 |pages=387–429 |doi=10.1146/annurev.matsci.30.1.387 |bibcode = 2000AnRMS..30..387G }}</ref><ref>{{cite book |last=Gschneidner |first=K. A. Jr. |last2=Pecharsky |first2=V. K. |year=2002 |chapter= |title=Fundamentals of Advanced Materials for Energy Conversion |editor1-first=D. |editor1-last=Chandra |editor2-first=R. G. |editor2-last=Bautista |location=Warrendale, PA |publisher=The Minerals, Metals and Materials Society |page=9 |isbn= }}</ref>
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| In 1997, the first near room temperature [[proof of concept]] magnetic refrigerator was demonstrated by [[Karl A. Gschneidner, Jr.]] by the [[Iowa State University]] at [[Ames Laboratory]]. This event attracted interest from scientists and companies worldwide who started developing new kinds of room temperature materials and magnetic refrigerator designs.<ref name="Ames"/>
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| A major breakthrough came 2002 when a group at the University of Amsterdam demonstrated the giant magnetocaloric effect in MnFe(P,As) alloys that are based on earth abundant materials.<ref>{{cite journal |last=Tegus |first=O. |last2=Brück |first2=E. |last3=de Boer |first3=F. R. |last4=Buschow |first4=K. H. J. |title=Transition-metal-based magnetic refrigerants for room-temperature applications |journal=[[Nature (journal)|Nature]] |volume=415 |issue=6868 |pages=150–152 |year=2002 |doi=10.1038/415150a |bibcode = 2002Natur.415..150T }}</ref>
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| Refrigerators based on the magnetocaloric effect have been demonstrated in laboratories, using magnetic fields starting at 0.6 T up to 10 T. Magnetic fields above 2 T are difficult to produce with permanent magnets and are produced by a [[superconducting magnet]] (1 T is about 20,000 times the [[Earth's magnetic field]]).
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| ===Room temperature devices===
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| Some recent research has focused on the use of the process to perform refrigeration near "room temperature". Constructed examples of room temperature magnetic refrigerators are listed in the table below:
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| {| class="wikitable" style="font-size:90%;"
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| |+Room temperature magnetic refrigerators
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| ! Institute/Company !! Location !! Announcement date !! Type !! Max. cooling power (W)<sup>[1]</sup>!! Max Δ''T ''(K)<sup>[2]</sup> !! Magnetic field (T) !! Solid refrigerant !! Quantity (kg)
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| |-
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| ! [[Ames Laboratory]]/Astronautics<ref>Zimm C, Jastrab A., Sternberg A., Pecharsky V.K., Gschneidner K.A. Jr., Osborne M. and Anderson I., Adv. Cryog. Eng. 43, 1759 (1998).</ref>
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| | Ames, Iowa/Madison, Wisconsin, USA || February 20, 1997 || Reciprocating || 600 || 10 || 5 (S)|| Gd spheres
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| |-
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| ! Mater. Science Institute Barcelona<ref>Bohigas X., Molins E., Roig A., Tejada J. and Zhang X.X., IEEE Trans. Magn. 36 538 (2000).</ref>
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| | Barcelona, Spain || May 2000 || Rotary ||?|| 5 || 0.95 (P) || Gd foil
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| |-
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| ! Chubu Electric/Toshiba<ref>Hirano N., Nagaya S., Takahashi M., Kuriyama T., Ito K. and Nomura S. 2002 Adv. Cryog. Eng. 47 1027</ref>
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| | Yokohama, Japan || Summer 2000 || Reciprocating || 100 || 21 || 4 (S)|| Gd spheres
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| |-
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| ! University of Victoria<ref>Rowe A.M. and Barclay J.A., Adv. Cryog. Eng. 47 995 (2002).</ref><ref>Rowe A.M. and Barclay J.A., Adv. Cryog. Eng. 47 1003 (2002).</ref><ref>Richard M.A., Rowe A.M. and Chahine R., J. Appl. Phys. 95 2146 (2004).</ref>
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| | Victoria, British Columbia Canada || July 2001 || Reciprocating || 2 || 14 || 2 (S) || Gd & Gd<sub>1−x</sub>Tb<sub>x</sub> L.B.
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| |-
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| ! Astronautics<ref>Zimm C, Paper No K7.003 Am. Phys. Soc. Meeting, March 4, Austin, Texas (2003) [http://www.aps.org/meet/MAR03/baps/tocK.html]</ref>
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| | Madison, Wisconsin, USA || September 18, 2001 || Rotary || 95 || 25 || 1.5 (P) || Gd spheres
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| |-
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| ! Sichuan Inst. Tech./Nanjing University<ref>Wu W., Paper No. K7.004 Am. Phys. Soc. Meeting, March 4, Austin, Texas (2003) [http://www.aps.org/meet/MAR03/baps/tocK.html]</ref>
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| | Nanjing, China || 23 April 2002 || Reciprocating || ? || 23 ||1.4 (P) ||Gd spheres and Gd<sub>5</sub>Si<sub>1.985</sub>Ge<sub>1.985</sub>Ga<sub>0.03</sub> powder
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| |-
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| ! Chubu Electric/Toshiba<ref name="aps.org">Hirano N., Paper No. K7.002 Am. Phys. Soc. Meeting March 4, Austin, Texas, [http://www.aps.org/meet/MAR03/baps/tocK.html]</ref>
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| | Yokohama, Japan || October 5, 2002 || Reciprocating || 40 || 27 || 0.6 (P) || Gd<sub>1−x</sub>Dy<sub>x</sub> L.B.
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| |-
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| ! Chubu Electric/Toshiba<ref name="aps.org"/>
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| | Yokohama, Japan || March 4, 2003 || Rotary ||60 ||10 ||0.76 (P) || Gd <sub>1−x</sub>Dy<sub>x</sub> L.B. || 1
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| |-
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| ! Lab. d’Electrotechnique Grenoble<ref>Clot P., Viallet D., Allab F., Kedous-LeBouc A., Fournier J.M. and Yonnet J.P., IEEE Trans. Magn. 30 3349 (2003).</ref>
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| | Grenoble, France || April 2003 || Reciprocating || 8.8 ||4 || 0.8 (P) || Gd foil
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| |-
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| ! George Washington University <ref>F. Shir, C. Mavriplis, L.H. Bennett, E. Della Torre, "Analysis of room temperature magnetic regenerative refrigeration," International Journal of Refrigeration, 28, 4 (2005) 616.</ref>
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| | USA || July 2004 || Reciprocating || ? ||5 || 2 (P) || Gd foil
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| |-
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| ! Astronautics<ref>Zimm C, Paper No. K7.003 Am. Phys. Soc. Meeting, March 4, Austin, Texas (2003) [http://www.aps.org/meet/MAR03/baps/tocK.html]</ref>
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| | Madison, Wisconsin, USA || 2004 || Rotary || 95 || 25 || 1.5 (P) || Gd and GdEr spheres / La(Fe<sub>0.88</sub>Si<sub>0.12</sub>)<sub>13</sub>H<sub>1.0</sub>
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| |-
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| ! University of Victoria<ref>Rowe A.M. and Tura A., International Journal of Refrigeration 29 1286–1293 (2006).</ref>
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| | Victoria, British Columbia Canada || 2006 || Reciprocating || 15 || 50 || 2 (S) || Gd, Gd<sub>0.74</sub>Tb<sub>0.26</sub> and Gd<sub>0.85</sub>Er<sub>0.15</sub> pucks || 0.12
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| |-
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| | colspan="8"| <sup>1</sup>maximum cooling power at zero temperature difference (Δ''T''=0); <sup>2</sup>maximum temperature span at zero cooling capacity (''W''=0); L.B. = layered bed; P = permanent magnet; S = superconducting magnet
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| In one example, Prof. Karl A. Gschneidner, Jr. unveiled a [[proof of concept]] magnetic refrigerator near room temperature on February 20, 1997. He also announced the discovery of the GMCE in Gd<sub>5</sub>Si<sub>2</sub>Ge<sub>2</sub> on June 9, 1997 <ref>{{cite web|url=http://prola.aps.org/abstract/PRL/v78/i23/p4494_1 |title=Phys. Rev. Lett. 78, 4494 (1997): Giant Magnetocaloric Effect in Gd_{5}(Si_{2}Ge_{2}) |publisher=Prola.aps.org |date= |accessdate=2012-10-04}}</ref> (see below). Since then, hundreds of peer-reviewed articles have been written describing materials exhibiting magnetocaloric effects.
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| ==See also==
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| * [[Electrocaloric effect]]
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| * [[Thermoacoustic refrigeration]]
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| * [[Dilution refrigerator]]
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| ==References==
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| {{Reflist|30em}}
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| 29. Gschneidner, K. Pecharsky, V. Tsokol, A. Recent Developments in Magnetocaloric Materials. Institute of Physics Publishing. March 17, 2005.
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| 30. Pecharsky, Vitalij. Gschneider, Karl. Magnetocaloric Effect and Magnetic Refrigeration. Journal of Magnetism and Magnetic Materials. October 1999.
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| ==Further reading==
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| *Lounasmaa, ''Experimental Principles and Methods Below 1 K'', Academic Press (1974).
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| *Richardson and Smith, ''Experimental Techniques in Condensed Matter Physics at Low Temperatures'', Addison Wesley (1988).
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| *Lucia, U. General approach to obtain the magnetic refrigeretion ideal Coefficient of Performance COP, ''Physica A: Statistical Mechanics and its Applications'', 387/14 (2008) 3477–3479, {{doi|10.1016/j.physa.2008.02.026}}; see also http://arxiv.org/abs/1011.1684
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| ==External links==
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| *[http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-adr.html NASA – How does an Adiabatic Demagnetization Refrigerator Work ?]
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| *[http://www.physlink.com/Education/AskExperts/ae488.cfm What is magnetocaloric effect and what materials exhibit this effect the most?]
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| *[http://www.sciencenews.org/pages/sn_arc98/3_28_98/fob3.htm Magnetocaloric materials keep fridges cool by C. Wu]
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| *[http://www.ameslab.gov/News/release/crada.html Ames Laboratory news release, May 25, 1999, Work begins on prototype magnetic-refrigeration unit].
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| *[http://www.eurekalert.org/features/doe/2001-11/dl-mrs062802.php Magnetic refrigerator successfully tested]
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| <!--these links repeat the same press release *[http://www.ameslab.gov/final/News/2001rel/01magneticrefrig.htm Ames Laboratory new release - Magnetic refrigerator successfully tested] | |
| *[http://www.hinduonnet.com/thehindu/seta/2002/02/07/stories/2002020700040500.htm The Hindu – Refrigerator sans compressor] the following one didn't load, someone else can try it
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| *[http://wint.decsy.ru/nanoworld/DATA/CLUB/overuni/paper34.htm]-->
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| *[http://lorien.ncl.ac.uk/ming/cleantech/refrigeration.htm Refrigeration Systems] Terry Heppenstall's notes, University of Newcastle upon Tyne (November 2000)
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| *[http://www.universe.nasa.gov/xrays/programs/astroe/eng/adr.html XRS Adiabatic Demagnetization Refrigerator]
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| *[http://www.cs.wpi.edu/~dfinkel/Sponsor/PH1.doc Executive Summary: A Continuous Adiabatic Demagnetization Refrigerator] ([[.doc]] format) ([http://google.com/search?q=cache:www.cs.wpi.edu/~dfinkel/Sponsor/PH1.doc Google cache])
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| <!--advert without explanations *[http://www.cmr.uk.com/cmrhome.html http://www.cmr.uk.com/cmrhome.html Welcome to Cambridge Magnetic Refrigeration]--> | |
| *[http://link.aps.org/doi/10.1103/PhysRevB.79.014435 Origin and tuning of the magnetocaloric effect in the magnetic refrigerant Mn1.1Fe0.9(P0.8Ge0.2)]
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| *[http://www.basf.com/group/pressrelease/P-09-348 Magnetic technology revolutionizes refrigeration]
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| *[http://arxiv.org/abs/1011.1684 Evaluation of thermodynamic quantities in magnetic refrigeration]
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| {{Emerging technologies}}
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| [[Category:Thermodynamic cycles]]
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| [[Category:Cooling technology]]
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| [[Category:Statistical mechanics]]
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| [[Category:Condensed matter physics]]
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| [[Category:Magnetism]]
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| [[Category:Emerging technologies]]
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