Magnetic properties and large magnetocaloric effects of GdPd intermetallic compound

With the intention to explore excellent magnetocaloric materials, the intermetallic compound GdPd was synthesized by arc melting and heat treatment. The microstructure, magnetic and magnetocaloric properties of the intermetallic compound of GdPd were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM) and the physical property measurement system(PPMS). A large reversible magnetocaloric effect is observed in GdPd accompanied by a second order magnetic phase transition from paramagnetism to ferromagnetism at ～39 K. The paramagnetic Curie temperature(θp) and the effective magnetic moment(μ_(eff))are determined to be 34.7 K and 8.12 μ_B/Gd,respectively. The maximum entropy change(|△S_M~(Max)|) and the relative cooling power(RCP) under a field change of 5 T are estimated to be 20.14 J/(kg·K) and 433 J/kg, respectively. The giant reversible magnetocaloric effects(both the large△S_M and the high RCP) together with the absence of thermal and field hysteresis make the GdPd compound an attractive candidate for low-temperature magnetic refrigeration.     

Magnetic properties and magnetocaloric effects of manganite (La_0.8Ho_0.2)_2/3Ca_1/3MnO₃ and (La_0.5Ho_0.5)_2/3Ca_1/3MnO₃

We reported the magnetic properties and magnetocaloric effects(MCE) of(La0.8Ho0.2)2/3Ca1/3MnO3 and(La0.5Ho0.5)2/3Ca1/3MnO3 nanoparticles by sol-gel technique.With this method,we were able to obtain the samples with particle diameters ranging from 50 to 200 nm.In the(La1-xHox)2/3Ca1/3MnO3 compound,an external magnetic field induced a magnetic transition from an paramagnetic phase to a ferromagnetic phase above Ts=105-135 K,leading to magnetocaloric effects.The maximum value of ΔSM was 1.19 J/(kg·K) at 100 K and 2.03 J/(kg·K) at 152 K for a magnetic field change of 5 T.Because both samples had large relative cooling power(RCP) and wide δTFWHM,the study on systems with the(La1-xHox)2/3Ca1/3MnO3-related magnetic transitions may open an important field in searching good magnetic materials.     

Influence of cooling rate on magneto-structural transition and magnetocaloric effect of Ni30Cu8Co12Mn37Ga13 alloy

The influence of heat treatment with different cooling rates on phase transition behaviors and magnetocaloric effect is systematically studied.Difference in atomic order is induced by changing cooling rates,where ordered phase is obtained in the furnace cooled(FC)sample while disordered phase is reserved in the water quenched(WQ)sample.The coupled magneto-structural transition is detected in both samples but the characteristic temperature significantly shifts to lower temperatures with increasing atomic order.Giant magnetic entropy change(ΔS_(mag))derived from magnetic field induced martensitic transformation is confirmed for both samples,and can be remarkably enhanced by the atomic ordering.The largestΔS_(mag) of 20.9J/(kg·K)is obtained at 307.5Kunder 5Tin the FC sample.     

Influence of partial substitution of cerium for lanthanum on magnetocaloric properties of La_(1–x)Ce_xFe_(11.44)Si_(1.56) and their hydrides

The structure and magnetocaloric properties of La1–xCexFe11.44Si1.56 and their hydrides La1–xCexFe11.44Si1.56Hy（x=0, 0.1, 0.2, 0.3, 0.4） were investigated.The samples crystallized mainly in the cubic Na Zn13-type structure with a small amount of α-Fe phase as impurity.The lattice constants and Curie temperature presented the same change tendency with increasing of Ce content.For the hydrides, the influence of Ce content on lattice constants was weakened and the values of H concentration y were approximate to be 1.56.The La1–xCexFe11.44Si1.56 compounds exhibited large values of isothermal entropy change –ΔSm around the Curie temperature TC under a low magnetic field change of 1.5 T.The value of –ΔSm increased and then decreased with increasing Ce content, reached the maximum, 26.07 J/kg·K for x=0.3.TC increased up to the vicinity of room temperature by hydrogen absorption for the Ce substituted compounds, but TC only slightly decreased with increasing Ce content.The first-order metamagnetic transition was still kept in the hydrides and the maximum values of –ΔSm were lower than those of the La1–xCexFe11.44Si1.56 compounds, but still remained large values, about 10.5 J/kg K under a magnetic field change of 1.5 T.The values of –ΔSm were nearly independent of the Ce content and did not increase with increasing x for the hydrides.The La1–xCexFe11.44Si1.56Hy（x=0–0.4） hydrides exhibited large magnetic entropy changes, small hysteresis loss and effective refrigerant capacity covered the room temperature range from 305 to 317 K.These hydrides are very useful for the magnetic refrigeration applications near room temperature under low magnetic field change.     

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys

Phase structure and magnetocaloric effect of （Tb1-xDyx）Co2 alloys with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 were investigated using X-ray diffraction analysis, differential thermal analysis, and magnetization measurement. The samples were single phase with cubic MgCu2- type structure; with the increase of Dy content, Tc decreased from 240 K （TbCo2） to 130 K （DyCo2）, and the maximum magnetic entropy change ｜ △SM,max｜ increased from 3.133 to 8.176 J/kg-K under low magnetic field of 0-2 T. The Arrott plot and the change of ｜△SM,max｜ showed that magnetic phase transition from second order to first order occured with the increase of Dy content between x=-0.6 and 0.8.     

Effect of praseodymium and cobalt substitution on magnetic properties and structures in La(Fe_(1–x)Si_x)_(13) compounds

Magnetic properties and structures in La1-zPrz(Fe0.895–xCoxSi0.105)13 (x=0.07, 0.08; z=0, 0.2, 0.4) compounds were investigated. When Pr and Co substituted for La and Fe, the Curie temperature of the compounds was adjusted to around room temperature. The magnetic phase transition was driven from first-order to second-order due to Co substitution. As a second-order phase transition material, the MCE of La0.6Pr0.4(Fe0.825Co0.07Si0.105)13, whose relative cooling power was 175 J/kg under a field change of 2 T, ...     

Influence of the Erbium Substitution for Gd in Gd5Si1.8Ge2.2Alloys on the Magnetocaloric Effect in Low-Field

The phases and magnetocaloric effect in the alloys (Gd1-xErx)5Si1.8Ge2.2 with x=0,0.1,0.2 and 0.3 were investigated by X-ray diffraction analysis and magnetization measurement. The samples were single phase with the monoclinic Gd5Si2Ge2-type structure. With the increase of Er content, the Curie temperature (Tc) decreased obviously from 253K of the alloy with x=0 to 114K with x=0.3. The maximum magnetic entropy changed in the samples of (Gd1-xErx)5Si1.8Ge2.2 with x=0.0,0.1,0.2 and 0.3 were 6.88,8.32,9.59 and 10.24 J·kg-1·K-1 respectively in the applied field change of 0~2.0T.     

Magnetic properties and magnetic entropy change of perovskite manganites La_(0.9-x)Eu_xSr_(0.1)MnO_3(x=0.000,0.075) by experimental method and numerical fitting

Polycrystalline samples La_(0.9-x)EuxSr_(0.1)MnO_3(x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism(FM) characteristic in the temperature range of 15-125 K and 15-150 K respectively; the samples show preformed clusters in the temperature range of 125-343 K and 150-325 K, respectively, the samples show paramagnetism(PM)characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |△S_M| value of the samples is near the Curie temperature(Tc), and the value of|△S_M| reaches 2.76 and 3.03 J/(K kg), respectively. In addition, the relative cooling power(RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region(T 77 K).     

Effect of a magnetic field on magnetic entropy change in LaFe_（11.7）Si_（1.3） compound

The magnetocaloric effect of LaFe11.7Si1.3 compound was investigated under an external magnetic field up to 9 T.The magnetization changed drastically at the Curie temperature TC under different fields and TC increased with the applied fields.The magnetic entropy change |?SM| vs temperature peak consisted of a spike and a plateau.The spike was a spurious result,while the plateau part resulted from the field-induced itinerant-electron metamagnetic(IEM) transition above TC,which went up with magnetic fields increasing.The width of the magnetic entropy change increased with magnetic fields at a rate of dL?S /dT~4 K/T.     

Effects of manganese doping on magnetocaloric effect in Ge-rich Gd_5Ge_（2.05）Si_（1.95） alloy

The structure, magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy, X-ray powder diffraction, differential scanning calorimeter (DSC) and magnetization measurements. The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired. DSC measurements were performed to determine the transformation temperatures for each alloy. Both alloys exhibited the first order phase transition around room temperature. The alloys showed an anti-ferromagnetic transition around 60 K. The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation. The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T, respectively.     

Magnetocaloric effect in ErNi_2 melt-spun ribbons

ErNi2 ribbons were produced by rapid solidification using the melt spinning technique.Their structural,magnetic and magnetocaloric properties in the as-solidified state were studied by X-ray diffraction,scanning electron microscopy,magnetization and specific heat measurements.Samples are single phase with the MgCu_2-type crystal structure,a Curie temperature T_C of 6.8 K and a saturation magnetization at2 K and 5 T of 124.0 A·m~2/kg.For a magnetic field change μ_0△H of 5 T(2 T) ribbons show a maximum magnetic entropy change |△S_M~(peak)| of 24.1(16.9) J/(kg·K),and an adiabatic temperature change △T_(ad)~(max) of8.1(4.4) K;this is similar to the previously reported literature for bulk alloys that were processed through conventional melting techniques followed by prolonged thermal annealing.In addition,the samples also show slightly wider △S_M(T) curves with respect to bulk alloys leading to a larger refrigerant capacity.     

Structure,magnetism and magnetic thermal properties of heavy rare earth Tb_(1-x)Tm_xFeO_3(x=0.00,0.15,0.25) polycrystalline samples

Tb_(1-x)Tm_xFeO_3(x = 0.00,0.15,0.25) polycrystalline series were synthesized using a solid-state reaction.Our results show that all three prepared samples are in a distorted orthogonal structure and their space group is pbnm.When the Tm~(3+)doping amount increases,the characteristics of the spin-flip of the sample decreases following an initial increase at the beginning;the antiferromagnetic property almost reaches zero;the magnetization decreases at the beginning but increases later on.The maximum magnetic entropy change and magnetic refrigeration effect RCP are reduced at varying degrees.Under a 7 T magnetic field,the maximum magnetic entropy change,△S_(max),for the three samples of Tb_(1-x)Tm_xFeO_3 with x=0.00,0.15,0.25 is 13.78,-9.28,and 10.69 J/(K·kg),respectively;the magnetic refrigeration capacity(RCP) is 316.85,175.2,and 297.60 J/kg,respectively.In summary,doping with the element Tm reduces △S_(max) and RCP of the sample.Since the maximum magnetic entropy change and the cooling capacity for the three samples are relatively large,they can be used as an alternative for magnetic refrigerants.     

Corrosion behavior and magnetocaloric effect of FeNi(1J85) coated LaFe_(11.6)Si_(1.4)/Sn composites

The FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were prepared by hot pressing(HP). The microstructure,corrosion behavior and magnetocaloric effect(MCE) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites were investigated systematically. The results show that the corrosion resistance of FeNi coated LaFe_(11.6)Si_(1.4)Sn composites is better than that of LaFe_(11.6)Si_(1.4)/Sn composites in deionized water. The maximum magnetic entropy change((-△S_M)~(max)) and relative cooling power(RCP) of FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites are 13.30 J/(kg-K) and 146.25 J/kg, respectively, which are larger than that((-△S_M)~(max), 10.65 J/(kg·K) and RCP, 106.53 J/kg) of LaFe_(11.6)Si_(1.4)/Sn composites in a low magnetic field change of 2 T. FeNi coated LaFe_(11.6)Si_(1.4)/Sn composites possess a more negative slope. The improvement of magnetic properties is due to high permeability FeNi permalloy(1 J85) which improves the itinerant-electron metamagnetic(IEM) transition. So, the method of coating FeNi can provide a new idea for enhancing the corrosion resistance and magnetocaloric effect of La(Fe_xSi_(1-x))_(13)-based materials.     

Phase transition and magnetocaloric effect of Ni55.2Mn18.6Ga26.2-xGdx (x=0, 0.05, 0.15) alloys

Phase transition process and magnetic entropy change -ΔS of Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys were studied.Ni55.2Mn18.6Ga26.2-xGdx(x=0, 0.05, 0.15) alloys still underwent simultaneous structural and magnetic transitions and transform from ferro-magnetic martensitic phase to paramagnetic austenitic phase during heating. Under a field of 2 T, the maximum magnetic entropy change -ΔSM of Ni55.2Mn18.6Ga26.15Gd0.05 alloy was 7.7 J/kg.K at 317 K during heating and 8.6 J/kg.K at 314 K during cooling while it was 11.8 J/kg.K at 317 K in Ni55.2Mn18.6Ga26.05Gd0.15alloy during heating.     

Magnetocaloric effect of(Tb_(1-x)Ce_x)Co_2 alloys in low magnetic field

The phases in alloys(Tb1-xCex)Co2 with x=0,0.1,0.2,0.3,0.4 and 0.5 were investigated by X-ray diffraction analysis,and the magnetocaloric effect for x=0-0.4 was studied by magnetization measurement.The samples were almost single phase with MgCu2-type cubic structure.The magnetization decreased with the increase of Ce.The Curie temperatures(Tc) of Tb1-xCexCo2 alloys with x from 0.1 to 0.4 were 180,165,160 and 152 K,respectively.For x=0.5 in the range from 100 K to 230 K,the point of magnetic transition was n...     

Mass production of magnetocaloric LaFeMnSiB alloys with hydrogenation

LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)Hxalloys were prepared by hydrogenation.Samples were annealed at 1343Kfor30-90 hto form the NaZn13 phase.La-rich andα-Fe secondary phases were also detected.Saturated hydrogenation at 553 Kand 0.15 MPa of H_2 pressure for 5hwas employed to improve the Curie temperature of the alloys to 279 K.The maximum magnetic entropy change,relative cooling power,and adiabatic temperature change of LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)H_x annealed at 1343 Kfor 90hafter hydrogen absorption are 6.38J/(kg·K)(magnetic changesμ0ΔH =1.65T),100.1J/kg(μ0ΔH =1.65T),and 2.2 K(μ0ΔH =1.48T),respectively.Although the maximum magnetic entropy change of the LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)H_x alloys is lower than those of similar alloys with high purity raw materials,the relative cooling power is nearly the same.The effect of impurities of the raw materials used was also discussed.It is assumed that the impurity of 0.2wt.% Al is responsible for the reduced entropy change of the resulted alloys.The LaFe_(11.39)Mn_(0.35)Si_(1.26)B_(0.1)H_x alloys prepared by this method could be a low cost alternative material for room temperature magnetic cooling applications.     

Influence of iron on phase and magnetic property of the LaFe_（11.6）Si_（1.4） compound

The phase relation, microstructure, Curie temperatures, hysteresis, and magnetocaloric effects of LaFex*11.6Si1.4 (x=0.96, 0.98, 1.0, and 1.02) compounds prepared by arc-melting and then annealed at 1423 K (1.5 h)+1523 K (4.5 h) were investigated. The main phase was NaZn13-type phase, the impurity phases included a small amount of α-Fe and LaFeSi phase in four samples. The crystal cell parameters of 1:13 phase increased from 1.1433(5) to 1.1454(4) nm with x increasing from 0.96 to 1.02, respectively. All samples kept the typical first-order magnetic transition. The increase of Fe strengthened IEM behavior, and led to the remarkable enhancement of MCE effect and negative slopes in Arrott plots around TC. The maximum ΔSM (T, H) under a low magnetic field (0-2 T) was 15.3, 16.8, 17.9, and 24.7 J/kg K with increasing of Fe content from x=0.96 to 1.02, respectively.     

Magnetocaloric and magneto-transport properties of Gd10Co20Si70 alloy

We report the results of magnetic, thermodynamic, transport and magnetocaloric effect (MCE) studies of newly synthesized Gd_(10)Co_(20)Si_(70) alloy. These measurements confirm an antiferromagnetic transition at T_N=9 K. Both MCE and magnetoresistance (MR) show quadratic dependence on the applied magnetic field, indicating the presence of spin fluctuations in the alloy. The maximum values of the magnetic entropy change determined from the isothermal magnetization data for magnetic field change of 7 and9 T are found to be 10.5 and 15.6 J/kg·K, respectively. As a consequence of the spin fluctuations effect, the MCE peaks are pulled towards high temperature side as asymmetrically broadened peak. The MR attains a large positive value of 73%at 2 K in 8 T. The large MR and reversible MCE make this alloy an attractive multifunctional magnetic material.     

Large magnetocaloric effect in Er_2O_3 compounds at cryogenic temperature

We investigated the magnetocaloric effect in commercial Er_2 O_3 powders which presents almost no hysteresis losses at low temperature.At a magnetic field change of 5 T,it displays large magnetic entropy change(-ΔS_M)_(max) of 15.02 J/(kg·K) and a refrigerant capacity(RC) of 311 J/K at Neel temperature T_N=3.32 K.The magnetic transition was found to be of a second-order.The maximum values of adiabatic temperature change(ΔT_(ad))_(max) reach 0.70 K for a magnetic field change of 1 T.The large value,of(-AS_M)_(max) as well as no hysteresis loss,makes Er_2 O_3 a promising material as a magnetic refrigerant at low temperature.     

Study on Gd-Si-Ge Alloys Using Domestic Gd

To evaluate the possibility of using Gd-Si-Ge alloys in magnetic refrigerators, samples of Gd-Si-Ge alloys were made of domestic Gd. The magnetocaloric effect of samples was estimated by magnetic entropy change (-△ASm) calculated from M-H curves according to Maxwell relation. The first order phase transformation was destroyed due to the impuritiesin the commercial Gd, so that no giant magnetocaloric effect was found. The samples made of purified Gd exhibit first order phase transformation, and the -△Sm is basically consistent with the published data of Ames laboratory, USA. This work proves that Gd-Si-Ge alloys made of domestic Gd can be utilized in magnetic refrigerators.