Magnetocaloric Effect Thesis Statement

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Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Recommended Citation

Md Din, Muhamad Faiz, Magnetic phase transitions and novel materials for magnetocaloric effect, Doctor of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2014. http://ro.uow.edu.au/theses/4371

Abstract

The magnetic and structural properties of some selected magnetocaloric materials such as La (Fe, Si)13 series compounds, RMn2X2 series (R=rare earth and X=Si or Ge) compounds and typical MM′X series (M, M′ = transition metal, X = Si, Ge, Sn) have been systematically investigated in this thesis with total 7 chapters being included. After a general introduction in Chapter 1, the description of theoretical aspects of the research and experimental techniques are given in Chapters 2 and 3, respectively.

In Chapter 4, the investigation on structure and magnetic properties of the La0.7Pr0.3Fe11.4- xCuxSi1.6 and La0.7Pr0.3Fe11.4-xCrxSi1.6 compounds is presented. Cu substitution for Fe in La0.7Pr0.3Fe11.4-xCuxSi1.6 (x = 0, 0.06, 0.12, 0.23, 0.34) leads to a reduction in hysteresis loss, a decrease in magnetic entropy change but an increase in Curie temperature (TC). The influences of annealing processes at different temperatures on TC, magnetic hysteresis, and the magnetocaloric effect (MCE) of La0.7Pr0.3Fe11.4Si1.6 are also investigated in detail. It has been found that a short-time and high temperature annealing process has benefits for the formation of the NaZn13 types as phase compared to a long-time and low temperature annealing process.

Furthermore, the effects of substitution Fe by Cr in NaZn13-type La0.7Pr0.3Fe11.4-xCrxSi1.6 (x=0, 0.06, 0.12, 0.26, and 0.34) compounds have been investigated by high intensity of X-ray and neutron diffraction, scanning electron microscopy, specific heat, and magnetization measurement. It has been found that a substitution of Cr for Fe in this compounds leads to a decrease in the lattice parameter a at room temperature and a variation on TC. While the first order nature of magnetic phase transition around TC does not change with increasing Cr content up to x=0.34. High intensity X-ray and neutron diffraction study at variable temperatures for highest Cr concentration x=0.34 confirmed the presence of strong magnetovolume effect around TC and indicated the direct evidence of coexistence of two magnetic phases across magnetic transition as characteristic of first order nature. The values of -ΔSM around TC found to decrease from 17 J kg-1K-1 for x=0 to 12 J kg-1K-1 for x=0.06 and then increases with further increasing Cr content up to 17.5 J kg-1K-1 for x=0.34 under a change of 0–5 T magnetic field. The relative cooling power (RCP) also indicated the similar behaviour which is decrease from 390 J kg-1 for x=0 to 365 J kg-1 for x=0.06 at the beginning and then increases up to 400 J kg-1 for x=0.34 at the same field applied.

Chapter 5 describes the investigation on magnetic behaviour and magnetocaloric effects of RMn2X2-based materials (R=rare earth and X=Si or Ge). The RMn2X2 series has attracted significant interest in recent years due primarily to their natural layered structure in which R and Mn atoms lie in alternate layers, separated by layers of X atoms. The strong dependence of the Mn–Mn magnetic exchange interaction on the intralayer near neighbour distance, and the interplay between the magnetism of the Mn and R layers lead to a fascinating arrangement of magnetic phases for these compounds. Firstly, in order to clarify the effect of substitution Mn with other transition metal (T) in NdMn2Si2 compound, structural and magnetic properties of the intermetallic compounds NdMn2−xTxSi2 (T=Ti, Cr, Cu and V) have been studied.

The Curie temperature and N´eel temperature of NdMn2Si2 decrease from TC = 36 K and TN = 380 K to TC = 14 K and TN = 360 K, respectively, on substitution of Ti (x = 0.3) for Mn. The magnetocaloric effect around TC, has been investigated in detail. Under a change of magnetic field of 0–5 T, the maximum value of the magnetic entropy change is 27 J kg-1K-1 for x = 0, reducing to 15.3 J kg-1K-1 for x = 0.1 and 10 J kg-1K-1 for x = 0.3; importantly, no thermal or field hysteresis losses occur with increase in Ti concentration. Combined with the lack of any hysteresis effects, these findings indicate that NdMn1.9Ti0.1Si2 compound offers potential as a candidate for magnetic refrigerator applications in the temperature region below 35 K.

In substitution Mn with Cr in NdMn2−xCrxSi2 compound, a giant magnetocaloric effect has been observed around Curie temperature, TC~42 K, in NdMn1.7Cr0.3Si2 with no discernible thermal and magnetic hysteresis losses. Detailed study shown that below 400 K, three magnetic phase transitions take place around 380 K, 320 K and 42 K. High resolution synchrotron and neutron powder diffraction (10–400 K) analysis confirmed the magnetic phases transitions as follows: TNintra~380 K denotes the transition from paramagnetism to intralayer antiferromagnetism (AFl), TNinter~320 K represents the transition from the AFl structure to the canted antiferromagnetic spin structure (AFmc), while TC~42 K denotes the first order magnetic transition from AFmc to canted ferromagnetism (Fmc+F(Nd)) due to ordering of the Mn and Nd sub-lattices. The maximum values of the magnetic entropy change and the adiabatic temperature change, around TC for a field change of 5 T are evaluated to be -ΔSM~15.9 J kg-1K-1 and ΔTad~5 K, respectively. The first order magnetic transition associated with the low levels of hysteresis losses (thermal 1.7Cr0.3Si2 offers potential as a candidate for magnetic refrigerator applications in the temperature region below 45 K.

Furthermore, the structural and magnetic properties of NdMn2-xCuxSi2 compounds (x=0–1.0) also have been investigated. Substitution of Cu for Mn leads to an increase in the lattice parameter a but a decrease in c at room temperature. Two magnetic phase transitions have been found for NdMn2-xCuxSi2 compounds with TN for the antiferromagnetic ordering of Mnsublatttice and TC for the Nd-sublattice ferromagnetic ordering. TC increases significantly with increasing Cu content from 36 K at x=0 to 100 K at x=1.0. Moreover, it is found that the order of magnetic phase transition around TC also changes from first order at xM around TC decrease with increasing x from 27 J kg-1K-1 for x=0 to 0.5 J kg-1K-1 for x=1.0 under 0–5 T field. Refinement of neutron diffraction patterns for x=0.2 confirms the magnetic states detected by magnetic study and also indicates that the lattice constants a and c show a distinct variation around TC. Moreover, further study on substitution Mn with V in NdMn2Si2 compound shown the similar behaviour with the replacement Mn by Ti. Both TC and TN are found decrease with increasing V concentration accompany with decreasing magnetic entropy change as discussed in more detail in Chapter 5.

Secondly, we carry out investigations of the Pr1-xYxMn2Ge2 magnetic phase diagram as functions of both composition and Mn–Mn spacing using X-ray and neutron diffraction, magnetization and differential scanning calorimetry measurements. Pr1-xYxMn2Ge2 exhibits an extended region of re-entrant ferromagnetism around x=0.5 with re-entrant ferromagnetism at TCPr~ 50 K for Pr0.5Y0.5Mn2Ge2. The entropy values -ΔSM around the ferromagnetic transition temperatures TCinter from the layered antiferromagnetic AFl structure to the canted ferromagnetic structure Fmc (typically TCinter~330–340 K) have been derived for Pr1-xYxMn2Ge2 with x=0.0, 0.2, and 0.5 for ΔB=0–5 T. The changes in magnetic states due toY substitution for Pr are also discussed in terms of chemical pressure, external pressure, and electronic effects.

Thirdly, the structural and magnetic properties of CeMn2Ge2-xSix compounds with Si concentrations in the range x = 0.0–2.0 have been investigated. Substitution of Ge with Si leads to a monotonic decrease of both a and c along with concomitant contraction of the unit cell volume and significant modifications to the magnetic states - a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Sirich compounds. The magnetic phase diagram has been constructed over the full range of CeMn2Ge2-xSix compositions and co-existence of ferromagnetism and antiferromagnetism has been observed in both CeMn2Ge1.0Si1.0 and CeMn2Ge0.8Si1.2 compounds with novel insight provided by high resolution X-ray synchrotron radiation studies. This study has enabled the large variety of magnetic structures and magnetic phase transitions of CeMn2Ge2-xSix compounds and their related magnetic properties to be determined by controlling chemical concentration.

Finally in Chapter 6, the MnCoGe-based materials, as a typical MM′X (M, M′ = transition metal, X = Si, Ge, Sn) compound which undergoes a second-order phase transition as well as a crystallographic phase transition from the low temperature orthorhombic TiNiSi-type to the high temperature hexagonal Ni2In-type structure have been studied. An investigation on substituting Ge by other metalloids in MnCoGe1-xTx compounds (T = Al and Si) has been implemented in this thesis and it was found that an appropriate T concentration successfully shifted the structural change and magnetic phase transition into the temperature range of interest, leading to the attainment of a high contribution to the giant magnetocaloric effect (GMCE). MnCoGe1-xTx provides the best example for control of the temperature window in order to investigate the effects of the structural and magnetic transition on the total entropy change, providing an excellent vehicle for investigation of the field-induced martensitic transformation in GMCE materials. Thus, in an effort to understand the nature of the magnetic transition in MnTiGe0.97Al0.03, critical exponent analysis in the vicinity of the ferromagnetic (FM)–paramagnetic (PM) region has been performed. The outcomes revealed that this material undergoes a structural transition at ~ 420 K as well as a second-order ferromagnetic–paramagnetic transition at ~ 350 K. Finally, a temperature dependent neutron diffraction experiment has been performed and confirmed that there is a coupling of the structural transition and the magnetic phase transition.

Structural, magnetic and magnetocaloric properties of the Mn1-xTixCoGe also have been investigated using X-ray diffraction, DC magnetization and neutron diffraction measurements in order to define the effect of substitution Mn with Ti in MnCoGe compound. Substitution of Ti for Mn in the parent MnCoGe compound leads to a significant reduction in both structure change temperature, Tstr (from ~ 645 K for MnCoGe to ~ 235 K for Mn0.94Ti0.06CoGe and ~ 178 K for Mn0.9Ti0.1CoGe) and Curie temperature, TC (from ~ 345 K for MnCoGe to ~ 270 K for Mn0.94Ti0.06CoGe and ~ 280 K for Mn0.9Ti0.1CoGe). Moreover, all the critical exponents for Mn0.94Ti0.06CoGe and Mn0.9Ti0.1CoGe fulfil the Widom scaling law. The validity of the calculated critical exponents was confirmed by the scaling equation, with the magnetization, field, and temperature data obtained below and above TC collapsing onto two different curves. Thus, the scaling of the magnetization data above and below TC was obtained using the respective critical exponents, and the consistency of the values of the critical exponents determined by different methods confirm that the calculated exponents are unambiguous and intrinsic. The critical exponents determined are close to those predicted by the mean-field theory for long range interactions.

Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures, as well as the ranges used in common refrigerators. [1][2][3][4]

The effect was first observed by a German physicist Warburg (1881)[5] Subsequently by French physicist P. Weiss and Swiss physicist A. Piccard in 1917.[6] The fundamental principle was suggested by P. Debye (1926) and W. Giauque (1927).[7] 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 3
He refrigeration, that is pumping on the 3
He vapors).

The magnetocaloric effect[edit]

The magnetocaloric effect (MCE, from magnet and calorie) is a magneto-thermodynamic phenomenon in which a temperature change 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 demagnetization. In that part of the refrigeration process, a decrease in the strength of an externally applied magnetic field allows the magnetic domains of a magnetocaloric material to become disoriented from the magnetic field by the agitating action of the thermal energy (phonons) 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.

One of the most notable examples of the magnetocaloric effect is in the chemical element gadolinium and some of its alloys. Gadolinium's temperature increases when it enters certain magnetic fields. When it leaves the magnetic field, the temperature drops. The effect is considerably stronger for the gadolinium alloy (Gd
5Si
2Ge
2).[8]Praseodymium alloyed with nickel (PrNi
5) has such a strong magnetocaloric effect that it has allowed scientists to approach to within one milliKelvin, one thousandth of a degree of absolute zero.[9]

Equation[edit]

The magnetocaloric effect can be quantified with the equation below:

where 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.

From the equation we can see that magnetocaloric effect can be enhanced by:

  • applying a large field
  • using a magnet with a small heat capacity
  • using a magnet with a large change in magnetization vs. temperature, at a constant magnetic field

Thermodynamic cycle[edit]

The cycle is performed as a refrigeration cycle that is analogous to the Carnot refrigeration cycle, but with increases and decreases in magnetic field strength instead of increases and decreases in pressure. It 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.

  • Adiabatic magnetization: A magnetocaloric substance is placed in an insulated environment. The increasing external magnetic field (+H) causes the magnetic dipoles 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 substance is heated (T + ΔTad).
  • 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).
  • 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, measuring the disorder of the magnetic dipoles.[10]
  • Isomagnetic entropic transfer: The magnetic field is held constant to prevent the material from reheating. The material is placed in thermal contact with the environment to be refrigerated. Because the working material is cooler than the refrigerated environment (by design), heat energy migrates into the working material (+Q).

Once the refrigerant and refrigerated environment are in thermal equilibrium, the cycle can restart.

Applied technique[edit]

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 dipoles in the refrigerant. The stronger the magnetic field, the more aligned the dipoles are, corresponding to lower entropy and heat capacity because the material has (effectively) lost some of its internal 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 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 equipartitioned energy from the motion of the molecules, thereby lowering the overall temperature of a system with decreased energy. Since the system is now 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.

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 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.

Working materials[edit]

The magnetocaloric effect (MCE) 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. Thus, the materials considered for magnetic refrigeration devices should be magnetic materials with a magnetic phase transition temperature near the temperature region of interest.[11] For refrigerators that could be used in the home, this temperature is room temperature. The temperature change can be further increased when the order-parameter of the phase transition changes strongly within the temperature range of interest.[2]

The magnitudes of the magnetic entropy and the adiabatic temperature changes are strongly dependent upon the magnetic ordering process. The magnitude is generally small in antiferromagnets, ferrimagnets and spin glass systems but can be much larger for ferromagnets that undergo a magnetic phase transition. First order phase transitions are characterized by a discontinuity in the magnetization changes with temperature, resulting in a latent heat.[11] Second order phase transitions do not have this latent heat associated with the phase transition.[11]

In the late 1990s Pecharksy and Gschneidner reported a magnetic entropy change in Gd
5(Si
2Ge
2) that was about 50% larger than that reported for Gd metal, which had the largest known magnetic entropy change at the time.[12] This giant magnetocaloric effect (GMCE) occurred at 270K, which is lower than that of Gd (294K).[4] Since the MCE occurs below room temperature these materials would not be suitable for refrigerators operating at room temperature.[13] Since then other alloys have also demonstrated the giant magnetocaloric effect. These include Gd
5(Si
xGe
1−x)
4, La(Fe
xSi
1−x)
13H
x and MnFeP
1−xAs
x alloys,.[11][13] Gadolinium and its alloys undergo second-order phase transitions that have no magnetic or thermal hysteresis.[14] However, the use of rare earth elements makes these materials very expensive.

Current research has been used to describe alloys with a significant magnetocaloric effect in terms of a thermodynamic system. Literature says that Gd5(Si2Ge2) for example may be described as a thermodynamic system provided it satisfies the condition of being “a quantity of matter or region in space chosen for study”.[15] Such systems have become relevant to modern research in thermodynamics because they serve as plausible materials for the creation of high performance thermoelectric materials.

Ni
2Mn-X (X = Ga, Co, In, Al, Sb) Heusler alloys are also promising candidates for magnetic cooling applications because they have Curie temperatures near room temperature and, depending on composition, can have martensitic phase transformations near room temperature.[3] These materials exhibit the magnetic shape memory effect and can also be used as actuators, energy harvesting devices, and sensors.[16] When the martensitic transformation temperature and the Curie temperature are the same (based on composition) the magnitude of the magnetic entropy change is the largest.[2] In February 2014, GE announced the development of a functional Ni-Mn-based magnetic refrigerator.[17][18]

The development of this technology is very material-dependent and will likely not replace vapor-compression refrigeration without significantly improved materials that are cheap, abundant, and exhibit much larger magnetocaloric effects over a larger range of temperatures. Such materials need to show significant temperature changes under a field of two tesla or less, so that permanent magnets can be used for the production of the magnetic field.[19][20]

Paramagnetic salts[edit]

The original proposed refrigerant was a paramagneticsalt, such as ceriummagnesiumnitrate. The active magnetic dipoles in this case are those of the electron shells of the paramagnetic atoms.

In a paramagnetic salt ADR, the heat sink is usually provided by a pumped 4
He (about 1.2 K) or 3
He (about 0.3 K) cryostat. An easily attainable 1 T magnetic field is generally required for initial magnetization. The minimum temperature attainable is determined by the self-magnetization tendencies of the refrigerant salt, but temperatures from 1 to 100 mK are accessible. Dilution refrigerators 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

Eventually paramagnetic salts become either diamagnetic or ferromagnetic, limiting the lowest temperature that can be reached using this method.

Nuclear demagnetization[edit]

One variant of adiabatic demagnetization that continues to find substantial research application is nuclear demagnetization refrigeration (NDR). NDR follows the same principles, but in this case the cooling power arises from the 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.

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.

Commercial development[edit]

Research and a demonstration proof of concept device in 2001 succeeded in applying commercial-grade materials and permanent magnets at room temperatures to construct a magnetocaloric refrigerator[21]

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.[22] They hoped to introduce the first commercial applications of the technology by 2010.

As of 2013 this technology had proven commercially viable only for ultra-low temperature cryogenic applications available for decades. Magnetocaloric refrigeration systems are composed of pumps, motors, secondary fluids, heat exchangers of different types, magnets and magnetic materials. These processes are greatly affected by irreversibilities and should be adequately considered. At year-end, Cooltech Applications[23] announced that its first commercial refrigeration equipment would enter the market in 2014. Cooltech Applications launched their first commercially available magnetic refrigeration system on 20 June 2016. At the 2015 Consumer Electronics Show in Las Vegas, a consortium of Haier, Astronautics Corporation of America and BASF presented the first cooling appliance.[24] BASF claim of their technology a 35% improvement over using compressors[25]

Current and future uses[edit]

Thermal and magnetic hysteresis problems remain to be solved for first-order phase transition materials that exhibit the GMCE.[19]

One potential application is in spacecraft.

Vapor-compression refrigeration units typically achieve performance coefficients of 60% of that of a theoretical ideal Carnot cycle, much higher than current MR technology. Small domestic refrigerators are however much less efficient.[26]

In 2014 giant anisotropic behaviour of the magnetocaloric effect was found in HoMn
2O
5 at 10 K. The anisotropy of the magnetic entropy change gives rise to a large rotating MCE offering the possibility to build simplified, compact, and efficient magnetic cooling systems by rotating it in a constant magnetic field.[27]

In 2015 Aprea et al.[28] presented a new refrigeration concept, GeoThermag, which is a combination of magnetic refrigeration technology with that of low-temperature geothermal energy. To demonstrate the applicability of the GeoThermag technology, they developed a pilot system that consists of a 100-m deep geothermal probe; inside the probe, water flows and is used directly as a regenerating fluid for a magnetic refrigerator operating with gadolinium. The GeoThermag system showed the ability to produce cold water even at 281.8 K in the presence of a heat load of 60 W. In addition, the system has shown the existence of an optimal frequency f AMR, 0.26 Hz, for which it was possible to produce cold water at 287.9 K with a thermal load equal to 190 W with a COP of 2.20. Observing the temperature of the cold water that was obtained in the tests, the GeoThermag system showed a good ability to feed the cooling radiant floors and a reduced capacity for feeding the fan coil systems.

History[edit]

The effect was discovered first observed by a German physicist Warburg (1881)[5] Subsequently by French physicist P. Weiss and Swiss physicist A. Piccard in 1917.[6]

Major advances first appeared in the late 1920s when cooling via adiabatic demagnetization was independently proposed by Peter Debye in 1926 and chemistry Nobel LaureateWilliam F. Giauque in 1927.

It was first demonstrated experimentally by Giauque and his colleague D. P. MacDougall in 1933 for cryogenic purposes when they reached 0.25 K.[29] Between 1933 and 1997, advances in MCE cooling occurred.[30]

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.[8]

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 abundant materials.[31]

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).

Room temperature devices[edit]

Recent research has focused on near room temperature. Constructed examples of room temperature magnetic refrigerators include:

SponsorLocationAnnouncement dateTypeMax. cooling power (W)[1]Max ΔT (K)[2]Magnetic field (T)Solid refrigerantQuantity (kg)COP (-)[3]
Ames Laboratory/Astronautics[32]Ames, Iowa/Madison, Wisconsin, USFebruary 20, 1997Reciprocating600105 (S)Gd spheres
Mater. Science Institute Barcelona[33][34]Barcelona, SpainMay 2000Rotary ?50.95 (P)Gd foil
Chubu Electric/Toshiba[35]Yokohama, JapanSummer 2000Reciprocating100214 (S)Gd spheres
University of Victoria[36][37]Victoria, British Columbia CanadaJuly 2001Reciprocating2142 (S)Gd & Gd
1−xTb
x L.B.
Astronautics[38]Madison, Wisconsin, USSeptember 18, 2001Rotary95251.5 (P)Gd spheres
Sichuan Inst. Tech./Nanjing University[39]Nanjing, China23 April 2002Reciprocating ?231.4 (P)Gd spheres and Gd5Si1.985Ge1.985Ga0.03 powder
Chubu Electric/Toshiba[40]Yokohama, JapanOctober 5, 2002Reciprocating40270.6 (P)Gd
1−xDy
x L.B.
Chubu Electric/Toshiba[40]Yokohama, JapanMarch 4, 2003Rotary60100.76 (P)Gd
1−xDy
x L.B.
1
Lab. d’Electrotechnique Grenoble[41]Grenoble, FranceApril 2003Reciprocating8.840.8 (P)Gd foil
George Washington University [42]USJuly 2004Reciprocating ?52 (P)Gd foil
Astronautics[43]Madison, Wisconsin, US2004Rotary95251.5 (P)Gd and GdEr spheres / La(Fe
0.88Si130−
0.12H
1.0
University of Victoria[44]Victoria, British Columbia Canada2006Reciprocating15502 (S)Gd, Gd
0.74Tb
0.26 and Gd
0.85Er
0.15 pucks
0.12
University of Salerno[45]Salerno, Italy2016Rotary250121.2 (P)Gd 0.600 mm spherical particles1.200.5 - 2.5
1maximum cooling power at zero temperature difference (ΔT=0); 2maximum temperature span at zero cooling capacity (W=0); L.B. = layered bed; P = permanent magnet; S = superconducting magnet; 3 COP values under different operating conditions

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
5Si
2Ge
2 on June 9, 1997.[12] Since then, hundreds of peer-reviewed articles have been written describing materials exhibiting magnetocaloric effects.

See also[edit]

References[edit]

  1. ^E.L.T. França, A.O. dos Santos, A.A. Coelho, L.M. da Silva. (2016). "Magnetocaloric effect of the ternary Dy, Ho and Er platinum gallides". Journal of Magnetism and Magnetic Materials. V. 401. P. 1088–1092. https://dx.doi.org/10.1016/j.jmmm.2015.10.138
  2. ^ abcBrück, E. (2005). "Developments in magnetocaloric refrigeration". Journal of Physics D: Applied Physics. 38 (23): R381. Bibcode:2005JPhD...38R.381B. doi:10.1088/0022-3727/38/23/R01. 
  3. ^ abKhovaylo, V. V.; Rodionova, V. V.; Shevyrtalov, S. N.; Novosad, V. (2014). "Magnetocaloric effect in "reduced" dimensions: Thin films, ribbons, and microwires of Heusler alloys and related compounds". Physica status solidi (b). 251 (10): 2104. Bibcode:2014PSSBR.251.2104K. doi:10.1002/pssb.201451217. 
  4. ^ abGschneidner, K. A.; Pecharsky, V. K. (2008). "Thirty years of near room temperature magnetic cooling: Where we are today and future prospects". International Journal of Refrigeration. 31 (6): 945. doi:10.1016/j.ijrefrig.2008.01.004. 
  5. ^ abWARBURG, E. G. Magnetische Untersuchungen über einige Wirkungen der Coerzitivkraft. Annalen der Physik (Leipzig), v. 13, p. 141-164, 1881.
  6. ^ abWeiss, Pierre; Piccard, Auguste (1917). "Le phénomène magnétocalorique". J. Phys. (Paris). 5th Ser. (7): 103–109. 
    Smith, Anders (2013). "Who discovered the magnetocaloric effect?". The European Physical Journal H. 38 (4): 507–517. Bibcode:2013EPJH...38..507S. doi:10.1140/epjh/e2013-40001-9. 
  7. ^Zemansky, Mark W. (1981). Temperatures very low and very high. New York: Dover. p. 50. ISBN 0-486-24072-X. 
  8. ^ abKarl Gschneidner, Jr. & Kerry Gibson (December 7, 2001). "Magnetic Refrigerator Successfully Tested". Ames Laboratory News Release. Ames Laboratory. Archived from the original on March 23, 2010. Retrieved 2006-12-17. 
  9. ^Emsley, John (2001). Nature's Building Blocks. Oxford University Press. p. 342. ISBN 0-19-850341-5. 
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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.
Analogy between magnetic refrigeration and vapor cycle or conventional refrigeration. H = externally applied magnetic field; Q = heat quantity; P = pressure; ΔTad = adiabatic temperature variation

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