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.     

Magnetic properties, magnetoresistivity and magnetocaloric effect in GdxLa1-x.MnSi alloys

The results of magnetization, magnetoresistivity and magnetocaloric effect (MCE) studies performed on polycrystalline samples of the Gd_xLa_1−xMnSi (x=0.5, 0.6, 0.7, 0.8, 0.9, 1.0) compounds were presented. Complex measurements were carried out on the Gd_xLa_1−xMnSi compounds to determine the influence of substitution in the rare earth (R) sublattice on the magnetic and related properties of these compounds. The compounds with x≤0.6 demonstrated two magnetic phase transitions (ferromagnetic to paramagnetic and antiferro-magnetic to ferromagnetic) both of which were first order. Anomalies in the magnetocaloric effect, electroresistivity and magnetoresistivity were observed in the temperature ranges of the magnetic phase transitions. The temperature dependences of MCE and magnetoresistivity for these compounds correlated with the temperature dependence of magnetization.     

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.     

Magnetic Entropy Change of （Gd1-xREx）5Si4（RE = Dy, Ho） Alloys

Magnetic Entropy Change of (Gd_(1-x)RE_x)_5Si_4(RE=Dy, Ho) Alloys     

Structure and Magnetocaloric Effect in Tb（ Co1-xSnx）2 Alloys

Recently,researchonmagnetocaloriceffect(MCE)hasattractedagreatdealofinterestinrare earth(RE)basedcompoundsbecauseoftheirenergy efficiencyandenvironmentalsafetyformagneticrefrig eration.Afirst ordermagneticphasetransitionwas foundintheintermetalliccompoundsRECo2(RE=Er,Ho,Dy)withMgCu2typestructure[1,2],leadingtoa largemagneticentropychangeforthesecompounds,whereasasecond ordertransitionwasfoundinTbCo2andGdCo2.IntheintermetalliccompoundsRECo2,theloweringofd electronconcentrationbythesubst…     

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 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...     

Magnetocaloric Properties of （Gd1-x Tbx ）3 Al2 Compounds Near Room Temperature

Recentlytherehasbeenaninterestinmagneticrefrigerationstudiesduetoitspotentialasanenergysavingtechnology[1～ 5] .Theefficiencyofmagneticre frigerationcriticallydependuponmagneticrefriger ants .Forthebestrefrigerantperformance ,verylargeisothermalmagneticentropychangeΔSisrequired ,andthemaximumvalueofΔSmustexistoverawiderrangeoftemperatures[2 ] .Recentdiscoveryofgiantmagnetocaloriceffect(MCE)ΔSinfirst ordertransi tionmaterialsgivesfurtherimpulsetowardsthedevel opmentofbothnewmaterialsandmag…     

Tb3NiSi2合金磁相变与磁热性能研究

依据X射线衍射(XRD)与等温磁化曲线和等磁场变温磁化曲线,主要研究了Tb₃NiSi₂合金相结构与磁性相变和磁热性能。XRD表明,采用800℃保温14天,然后炉冷至室温的热处理方法制备的R3NiSi2(R=Tb,Dy,Ho,Er)合金中,主相均为Gd3NiSi2型正交结构(空间群:Pnma,No.62)相,但杂相R5Si3含量存在差异,其规律是从Er到Tb,含量依次减少,Tb₃NiSi₂合金样品基本为一个单相,其相应晶格常数分别为a=1.1240(8)nm,b=0.41009(8)nm,c=1.12058(1)nm。等温磁化曲线显示在50~300 K温度范围内,Tb₃NiSi₂合金仅展现出铁磁-顺磁相变,并没有在130,82,66,53 K等观察到相关文献报道的多重的反常反铁磁态-铁磁态(AFM-FM)相变。0.01 T磁场下的磁化强度对温度求导曲线(d M/d T)和0~2 T磁场下的Arrott图结果证实合金铁磁-顺磁二级磁相变居里温度(Tc)=88 K。居里外斯定理拟合表明合金中Tb³⁺粒子的有效磁矩为9.90μB(μB为玻尔磁子),同期望值μeff/Tb³⁺=g(J(J+1))1/2=9.72μB基本一致。在磁热性方面,Tb₃NiSi₂合金在0~2 T磁场范围内,低场响应性较差,铁磁态分子的有效磁矩远低于顺磁分子有效磁矩,最大磁熵变(-ΔSM_max)为3.2 J·kg^-1·K^-1;在对应的半高宽温跨(δTFWHM)=35.5K范围内,相对制冷量为113 J·kg^-1。     

Phase,microstructure, and magnetocaloric effect of the large disc LaFe11.6Si1.4 alloy

The large disc LaFe11.6Si1.4 alloy, which was prepared by medium-frequency induction furnace, was annealed at 1503 K for different time. The main phases were 1:13 phase in the edge parts of the large discs alloy; the impurity phases included α-Fe phase, LaFeSi phase, and even very small amount of La5Si3 phase. The amounts of impurity phases reduced with increasing in annealing time. The magnetic properties in the edge parts of the large discs LaFe11.6Si1.4 alloy were investigated. The magnetic susceptibility had an abrupt change at Curie temperature(TC) as the magnetization in M-T curves. The alloys had almost the same TC(191 K), the magnetocaloric effect(MCE) and relative cooling power(RCP) increased with increasing in annealing time. In addition, for the same alloy, the magnetic hysteresis decreased with the increase in temperature.     

Magnetic Properties of Nd12Co6Pb Compound

The magnetic and magnetocaloric properties for the Nd12Co6Pb compound were investigated. The Curie temperature TC of the magnetic transition of Nd12Co6Pb compound is 194 K. The experimentally determined magnetic effective paramagnetic moment is μeff=12.36 μB per formula unit (3.49 μB per Nd atom). The maximum magnetic entropy change in the low magnetic field changes of 0～2 T for the Nd12Co6Pb compound is about 215.0 J·mole-1·K-1.     

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.     

Syntheses and Characterization of Binuclear Complexes Tb（1-x）Eux（TTA）3 Phen

Rare earth ternary complexes Tb1-xEux（TTA）3Phen（x=0,0.25,0.5,0.75,1.0）were synthesized and characterized by DTA-TG,XRD and infrared（IR）.The photophysical properties of these complexes were studied in detail using ultraviolet absorption spectra and fluorescent spectra.Ultraviolet absorption showed that the energy absorption of the complexes mostly came from ligands.Infrared spectra of Tb1-xEux（TTA）3Phen complexes were similar to the pure complexes.TG curves proved that the complexes were stable.Tb3＋ emission was almost quenched and the Eu3＋ emission was enhanced by codoping the complexes.The Tb3＋ ion acted as an energy transfer bridge that helped energy transfer from poly（N-vinylcar-bazole（PVK）to Eu3＋.In addition,their PL and EL properties were systematically studied.     

Growth and characterization of ferroelectric Tb2（MoO4）3 crystal

By using Zb4O7 and MoO4 as starting materials, ferroelectric Tb2(MoO4)3 crystal was grown by the Czochralski method. The as-grown crystal was pale green color, transparent and crack-free. X-ray powder diffraction (XRPD), transmission spectrum, dielectric con-stant and polarization-electric field (P-E) hysteresis loop measurements were performed to characterize the crystal. The XRPD confirmed the as-grown crystal to be Tb2(MoO4)3. The transmission spectrum of the crystal showed that its transmittance in the entire visible and most near-infrared region was more than 70% except for an absorption peak around 486 nm. Obvious dielectric anomaly could be observed at low frequencies with increasing temperature through the dielectric constant measurement and the Curie temperature of Tb2(MoO4)3 crystal was determined to be 162.3℃. The unsaturated P-E hysteresis loops indicated that it was difficult for the ferroelectric domains in Tb2(MoO4)3 crystal to array regularly with repeated switching of the electric field.     

Magnetocaloric Effect in Colossal Magnetoresistance Material（ La0.6 Dy0.1 ） Sr0.3 MnO3

The magnetocaloric effect was discovered in 1881by Warburg[1]. When a magnetic field is applied to amagnetic material, the unpaired spins are aligned par allel to the magnetic field, which lowers the magneticentropy and causes the sample to heat up. I…     

Magnetostriction and Acoustics Properties of Tb1-xDyx(Fe1-yMny)1.95 Alloys and Their Application to Sonar Transducers

It was found in 1970s that Tbl -- x Dy.FeZalloys with C 15--type Laves phase structure had... [fi 1giant magnetostriction. Recent studies onthe substitution of Fe by other transition metalshave shown that magnetostrictive properties ofthe materials can he improved by the additionof transition metals. For example I the substitution of Mn for Fe in Tbl -- .Dy.FeZ alloys wasfound to increase the magnetostriction at lowmagnetic field and to influence the magnetocrystalline anisotropy of the r…     

Tuning structure and magnetic properties of table-like magnetocaloric effect in Er6MnSb2 by zirconium substitution

In this study,zirconium(Zr) successfully substituted for erbium(Er) in Er_6-xZr_xMnSb₂(x=0,0.5,1,1.5) of the Fe₂P type,with comprehensive characterizations on crystal structure,electronic structure and magnetic properties.According to synchrotron powder X-ray diffraction data analysis and density functional theory calculation,Zr does not randomly but preferentially occupy during the doping process and results in weaker magnetic exchange interactions and ...     

Surface modification of （Tb0.3Dy0.7）Fe1.95 alloy by ion nitriding process

Effect of ion nitriding modification on surface hardness, corrosion resistance and magnetostriction of (Tb0.3Dy0.7)Fe1.95 alloy was investigated. Results demonstrated that a 100-200 nm thick nitrided layer was formed on the sample surface by ion nitriding treatment, which improved obviously surface hardness, wear, and corrosion resistance properties of (Tb0.3Dy0.7)Fe1.95 alloys. The surface hardness was increased from HV587 to HV622 after ion nitriding at 650 K for 6 h. Furthermore, ion nitriding treatment had almost no influence on mag-netostrictive performance as the nitrided layer was quite thin and the treatment temperature was not too high. The results might provide us a new approach for surface modification of (Tb0.3Dy0.7)Fe1.95 alloy.