Magnetic entropy change and large refrigerant capacity of Ce6Ni2Si3-type GdCoSiGe compound

Magnetic entropy change (△S M) and refrigerant capacity (RC) of Ce 6 Ni 2 Si 3-type Gd 6 Co 1.67 Si 2.5 Ge 0.5 compounds have been investigated.The Gd 6 Co 1.67 Si 2.5 Ge 0.5 undergoes a reversible second-order phase transition at the Curie temperature T C=296 K.The high saturation magnetization leads to a large △S M and the maximal value of △S M is found to be 5.9 J/kg · K around T C for a field change of 0-5 T.A broad distribution of the △S M peak is observed and the full width at half maximum of the △S M peak is about 101 K under a magnetic field of 5 T.The large RC is found around T C and its value is 424 J/kg.     

Magnetocaloric effect in Gd6Co1.67Si3 compound with a second-order phase transition

The magnetic properties and the magnetic entropy change AS have been investigated for Gd6Co1.67Si3 compounds with a second-order phase transition. The saturation moment at 5 K and the Curie temperature TC are 38.1μB and 298 K, respectively. The AS originates from a reversible second-order magnetic transition around TC and its value reaches 5.2 J/kg.K for a magnetic field change from 0 to 5T. The refrigerant capacity （RC） of Gd6Co1.67Si3 are calculated by using the methods given in Refs.[12] and [21], respectively, for a field change of 0 5T and its values are 310 and 440 J/kg, which is larger than those of some magnetocaloric materials with a first-order phase transition.     

Giant magnetocaloric effect in the Gd5Ge2.025Si1.925In0.05 compound

The magnetocaloric properties of the Gd 5 Ge 2.025 Si 1.925 In 0.05 compound have been studied by x-ray diffraction,magnetic and heat capacity measurements.Powder x-ray diffraction measurement shows that the compound has a dominant phase of monoclinic Gd5Ge2Si2-type structure and a small quantity of Gd 5(Ge,Si) 3-type phase at room temperature.At about 270 K,this compound shows a first order phase transition.The isothermal magnetic entropy change(△SM) is calculated from the temperature and magnetic field dependences of the magnetization and the temperature dependence of MCE in terms of adiabatic temperature change(△Tad) is calculated from the isothermal magnetic entropy change and the temperature variation in zero-field heat-capacity data.The maximum S M is 13.6 J·kg-1·K-1 and maximum △Tad is 13 K for the magnetic field change of 0-5 T.The Debye temperature(θD) of this compound is 149 K and the value of DOS at the Fermi level is 1.6 states/eV·atom from the low temperature zero-field heat-capacity data.A considerable isothermal magnetic entropy change and adiabatic temperature change under a field change of 0-5 T jointly make the Gd5Ge2.025Si1.925 In 0.05 compound an attractive candidate for a magnetic refrigerant.     

Magnetic properties and magnetocaloric effects in amorphous and crystalline Gd55Co35Ni10 ribbons

The magnetic properties and magnetocaloric effects of amorphous and crystalline Gd55Co35Ni10 ribbons are investigated.A main phase with a Ho 12 Co 7-type monoclinic structure(space group P21/c) and a minor phase with a Ho4Co3-type hexagonal structure(space group P63/m) are obtained for crystalline ribbon after annealing.The amorphous ribbons order ferromagnetically and undergo a second-order transition at 192 K.For crystalline Gd55Co35Ni10 ribbons,two magnetic phase transitions occur at 158 and 214 K,respectively.The peak value of-△SM under a field change of 0-5 T is 6.5 J/kg K at 192 K for amorphous Gd55Co35Ni10 ribbons.A relatively large magnetic entropy change(～5.0 J/kg K) under a field change of 0-5 T for the crystalline Gd55Co35Ni10 ribbons is obtained in the temperature interval range of 154-214 K.The large platform of magnetic entropy change and the negligible thermal/magnetic hysteresis loss mean the crystalline Gd55Co35Ni10 compound can satisfy the requirement of the Ericsson-type refrigerator working in the temperature range from 154K to 214K.     

Order of magnetic transition and large magnetocaloric effect in Er3Co*

We have studied the magnetic and magnetocaloric properties of the Er3 Co compound,which undergoes ferromagnetic ordering below the Curie temperature TC = 13 K.It is found by fitting the isothermal magnetization curves that the Landau model is appropriate to describe the Er3 Co compound.The giant magnetocaloric effect(MCE) without hysteresis loss around T C is found to result from the second-order ferromagnetic-to-paramagnetic transition.The maximal value of magnetic entropy change is 24.5 J/kg.K with a refrigerant capacity(RC) value of 476 J/kg for a field change of 0-5 T.Large reversible MEC and RC indicate the potentiality of Er3 Co as a candidate magnetic refrigerant at low temperatures.     

Order of magnetic magnetocaloric transition and large effect in Er3Co

We have studied the magnetic and magnetocaloric properties of the Er3Co compound, which undergoes ferromagnetic ordering below the Curie temperature Tc = 13 K. It is found by fitting the isothermal magnetization curves that the Landau model is appropriate to describe the Er3Co compound. The giant magnetocaloric effect （MCE） without hysteresis loss around Tc is found to result from the second-order ferromagnetic-to-paramagnetic transition. The max- imal value of magnetic entropy change is 24.5 J/kg.K with a refrigerant capacity （RC） value of 476 J/kg for a field change of 0-5 T. Large reversible MEC and RC indicate the potentiality of Er3Co as a candidate magnetic refrigerant at low temperatures.     

Effect of Dy substitution on magnetic properties and magnetocaloric effects of Tb6Co1.67Si3 compounds

The magnetic and magnetocaloric properties of(Tb1-xDyx) 6 Co 1.67 Si 3(0 ≤ x ≤ 0.8) have been experimentally investigated.The compounds exhibit a Ce6Ni2Si3-type hexagonal structure and undergo a second-order magnetic transition.The Curie temperature decreases from ～ 187 K to 142 K as the content of Dy grows from 0 to 0.8.The maximal magnetic entropy change,for a field change of 0-5 T,varies between ～ 6.2 and ～ 7.4 J/kg.K,slightly decreasing when Dy is introduced.The substitution of Dy leads to a remarkable increase in refrigeration capacity(RC).A large RC value of ～ 626 J/kg is achieved for x = 0.4 under a field change of 0-5 T.     

Magnetic transition and large reversible magnetocaloric effect in EuCu1.75P2 compound

The magnetocaloric effect(MCE) in EuCu1.75P2 compound is studied by the magnetization and heat capacity measurements.Magnetization and modified Arrott plots indicate that the compound undergoes a second-order phase transition at TC ～ 51 K.A large reversible MCE is observed around TC.The values of maximum magnetic entropy change(-△SxMma) reach 5.6 J·kg-1·K-1 and 13.3 J·kg-1·K-1 for the field change of 2 T and 7 T,respectively,with no obvious hysteresis loss in the vicinity of Curie temperature.The corresponding maximum adiabatic temperature changes(△Tadmax) are evaluated to be 2.1 K and 5.0 K.The magnetic transition and the origin of large MCE in EuCu1.75P2 are also discussed.     

Low field induced giant anisotropic magnetocaloric effect in DyFeO_3 single crystal

We have investigated the anisotropic magnetocaloric effect and the rotating field magnetic entropy in Dy FeO3 single crystal. A giant rotating field entropy change of -ΔS R M= 16.62 J/kg·K was achieved from b axis to c axis in bc plane at 5 K for a low field change of 20 k Oe. The large anisotropic magnetic entropy change is mainly accounted for the 4 f electron of rare-earth Dy3+ ion. The large value of rotating field entropy change, together with large refrigeration capacity and negligible hysteresis, suggests that the multiferroic ferrite Dy FeO3 singlecrystal could be a potential material for anisotropic magnetic refrigeration at low field, which can be realized in the practical application around liquid helium temperature region.     

Large reversible magnetocaloric effect in HoMn2O5

Magnetocaloric effect (MCE) in polycrystalline HoMn2O5 was investigated by isothermal magnetization curves from 2 K to 50 K. A relatively large magnetic entropy change, △SM = 7.8 J/(kg · K), was achieved with the magnetic field up to 70 kOe (1 Oe = 79.5775 A · m-1). The magnetic entropy change is reversible in the whole range of temperature. The contributions of elastic and magnetoelastic energy to the changing of the magnetic entropy are discussed in terms of the Landau theory. The reversibility of MCE with maximal refrigerant capacity RC = 216.7 J/kg makes polycrystalline HoMn2O5 promising as a magnetic refrigerant.     

Table-Like Large Magnetocaloric Effect in the Misch Metal RSi Compound

Magnetic properties and the magnetocaloric effect(MCE)of the RSi(R=Ce,Pr,Nd)compounds made of Misch metal(MM)are investigated.Two transitions are found at 12K and 38K.Field variation generated large MCE and two peaks are found in the magnetic entropy change(△S)curves,which correspond to the two transition temperatures.The maximum values of the magnetic entropy changes(△S)are found to be-5.1 J/(kg·K)and-9.3 J/(kg·K)for the field ranges of 0-2 T and 0-5 T,respectively.The large AS as well as ultra-low price of MM make(MM)Si a competitive magnetic refrigerant candidate for low temperature in Eriksson cycle.     

Magnetic properties and magnetocaloric effects in HoPd intermetallic

A large reversible magnetocaloric effect accompanied by a second order magnetic phase transition from PM to FM is observed in the Ho Pd compound. Under the magnetic field change of 0–5 T, the magnetic entropy change-ΔS max M and the refrigerant capacity RC for the compound are evaluated to be 20 J/(kg·K) and 342 J/kg, respectively. In particular,large-ΔS max M(11.3 J/(kg·K)) and RC(142 J/kg) are achieved under a low magnetic field change of 0–2 T with no thermal hysteresis and magnetic hysteresis loss. The large reversible magnetocaloric effect(both the large-ΔS M and the high RC)indicates that Ho Pd is a promising material for magnetic refrigeration at low temperature.     

Magnetocaloric effect study of SrFe_(0.8)Co_(0.2)O_3 single crystal prepared under high pressure

A high-quality Sr Fe0.8Co0.2O3 single crystal is prepared by combining floating-zone and high-pressure treatment methods. Its Magnetocaloric effect is investigated by magnetic measurements. A paramagnetism-to-ferromagnetism transition is found at about 270 K and this transition is a second-order one in nature as confirmed by Arrott plots. The saturated moment obtained at 2 K and 7 T is 3.63 μB/f.u. The maximal value of magnetic entropy change measured at 5 T is about4.0 J·kg-1·K-1. The full wide at half maximum for a magnetic entropy change peak observed in Sr Fe0.8Co0.2O3 is considerably large. As a consequence, the relative cooling power value of Sr Fe0.8Co0.2O3 obtained at 5 T is 331 J/kg, which is greatly higher than those observed in other perovskite oxides. The present work therefore provides a promising candidate for magnetic refrigeration near room temperature.     

Magnetocaloric and barocaloric effects in a Gd5Si2Ge2 compound

The first-order phase transition in Gd5Si2Ge2 is sensitive to both magnetic field and pressure.It may indicate that the influences of the magnetic field and the pressure on the phase transition are virtually equivalent.Moreover,theoretical analyses reveal that the total entropy change is almost definite at a certain Curie temperature no matter whether the applied external field is a magnetic field or a pressure.The entropy change curve can be broadened dramatically under pressure,and the refrigerant capacity is improved from 284.7 J/kg to 447.0 J/kg.     

Magnetic entropy change and large refrigerant capacity of Ce6i2Si3-type GdCoSiGe compound

Magnetic entropy change (Δ S_M) and refrigerant capacity (RC) of Ce₆Ni₂Si₃-type Gd₆Co_1.67Si_2.5Ge_0.5 compounds have been investigated. The Gd₆Co_1.67Si_2.5Ge_0.5 undergoes a reversible second-order phase transition at the Curie temperature T_C = 296 K. The high saturation magnetization leads to a large Δ S_M and the maximal value of Δ S_M is found to be 5.9 J/kg,cdot,K around T_C for a field change of 0--5 T. A broad distribution of the Δ S_M peak is observed and the full width at half maximum of the Δ S_M peak is about 101 K under a magnetic field of 5 T. The large RC is found around T_C and its value is 424 J/kg.     

Magnetism and giant magnetocaloric effect in rare-earth-based compounds R_3BWO_9(R = Gd,Dy, Ho)

The magnetism and magnetocaloric effect(MCE) of rare-earth-based tungstate compounds R_3 BWO_9(R=Gd,Dy,Ho) have been studied by magnetic susceptibility,isothermal magnetization,and specific heat measurements.No obvious long-range magnetic ordering can be found down to 2 K.The Curie-Weiss fitting and magnetic susceptibilities under different applied fields reveal the existence of weak short-range antiferromagnetic couplings at low temperature in these systems.The calculations of isothermal magnetization exhibit a giant MCE with the maximum changes of magnetic entropy being 54.80 J/kg-K at 2 K for Gd_3 BWO_9,28.5 J/kg-K at 6 K for Dy_3 BWO_9,and 29.76 J/kg-K at 4 K for Ho_3 BWO_9,respectively,under a field change of 0-7 T.Especially for Gd_3 BWO_9,the maximum value of magnetic entropy change(-ΔS_M~(max)) and adiabatic temperature change(-ΔT_(ad)~(max)) are 36.75 J/kg·K and 5.56 K for a low field change of 0-3 T,indicating a promising application for low temperature magnetic refrigeration.     

Large reversible magnetocaloric effect induced by metamagnetic transition in antiferromagnetic HoNiGa compound

The magnetic properties and magnetocaloric effects(MCE) of Ho Ni Ga compound are investigated systematically.The Ho Ni Ga exhibits a weak antiferromagnetic(AFM) ground state below the Neel temperature TNof 10 K, and the AFM ordering could be converted into ferromagnetic(FM) ordering by external magnetic field. Moreover, the field-induced FM phase exhibits a high saturation magnetic moment and a large change of magnetization around the transition temperature,which then result in a large MCE. A large-?S_M of 22.0 J/kg K and a high RC value of 279 J/kg without magnetic hysteresis are obtained for a magnetic field change of 5 T, which are comparable to or even larger than those of some other magnetic refrigerant materials in the same temperature range. Besides, the μ_0H~(2/3)dependence of |?S_M~(pk)| well follows the linear fitting according to the mean-field approximation, suggesting the nature of second-order FM–PM magnetic transition under high magnetic fields. The large reversible MCE induced by metamagnetic transition suggests that Ho Ni Ga compound could be a promising material for magnetic refrigeration in low temperature range.     

Giant magnetocaloric effect in Tb5Ge2-xSi2-xMn2x compounds

The crystal structure,magnetic and magnetocaloric characteristics of the pseduo ternary compounds of Tb5Ge2 xSi2 xMn2x(0 ≤ 2x ≤ 0.1) were investigated by x-ray powder diffraction and magnetization measurements.The x-ray powder diffraction results show that all compounds preserve the monoclinic phase as the majority phase and all the synthesized compounds were observed to be ferromagnetic from magnetization measurements.Magnetic phase transitions were interpreted in terms of Landau theory.Maximum isothermal magnetic entropy change value(20.84 J.kg-1.K-1) was found for Tb5Ge1.95Si1.95Mn0.1 at around 123 K in the magnetic field change of 5 T.     

Effect of Al Addition on the Glass-Forming Ability and Magnetic Properties of a Gd-Co Binary Amorphous Alloy

The glass-forming ability(GFA) and magnetic properties of the Gd_(50) Coso-based amorphous aiioy with Al addition substitution for Co are investigated.It is found that the GFA and magneto-caloric effect of the Gd_(50)Co_(45)Al_5amorphous aiioy are better than Gd_(50)Co_(50) amorphous alloy.The maximum magnetic entropy change(-△S_m~(peak))and the magnetic refrigerant capacity of the amorphous alloy under a field of 5T are about 6.64 J·kg~(-1)K~(-1) and764 J·kg~(-1),respectively.The field dependence of magnetic entropy change meets the one predicted by the mean field theory,which is investigated for a better understanding of the magneto-caloric behaviors of the Gd_(50)Co_(45)Al_5amorphous alloy.     

Martensitic transformation and giant magnetic entropy change in Ni_(42.8)Mn_(40.3)Co_(5.7)Sn_(11.2) alloy

The crystal structure, phase transition, and magnetocaloric effect in Ni42.8Mn40.3Co5.7Sn11.2 alloy are investigated by structure analysis and magnetic measurements. A large magnetic entropy change of 45.6 J/kg.K is obtained at 215 K under a magnetic field of 30 kOe （1 Oe = 79.5775 A.m-1）. The effective refrigerant capacity of Ni42.8Mn40.3Co5.7Sn11.2 alloy reaches 72.1 J/kg under an applied field changing from 0 to 30 kOe. The external magnetic field shifts the martensitic transition temperature about 3-4 K/10 kOe towards low temperature, indicating that magnetic field can retard the phase transition to a certain extent. The origin of large magnetic entropy change is discussed in the paper.