Magnetic and electrical properties of RCo2Mn (R=Ho, Er) compounds

The RCo₂Mn (R=Ho and Er) alloys, crystallizing in the cubic MgCu₂-type structure, are isostructural to RCo₂ compounds. The excess Mn occupies both the R and the Co atomic positions. Magnetic, electrical and heat capacity measurements have been done in these compounds. The Curie temperature is found to be 248 and 222 K for HoCo₂Mn and ErCo₂Mn, respectively, which is considerably higher than that of the corresponding RCo₂ compounds. Saturation magnetization values in these samples are less compared to that of the respective RCo₂ compounds.     

Magnetic and magnetocaloric properties of R6Mn23 (R=Y, Nd, Sm, Gd-Tm, Lu) compounds

The magnetic and magnetocaloric properties of the R₆Mn₂₃ compounds (R=Y, Nd, Sm, Gd-Tm, Lu) are investigated from DC magnetization measurements. The results are analyzed and discussed in connection with previously published data. These binaries crystallize in the cubic Th₆Mn₂₃ type of structure (Fm-3m). The Mn sublattice orders at high temperature (398 K≤T_C≤505 K) with a collinear ferrimagnetic structure. The R sublattice orders at lower temperature (<100 K) with a non-collinear arrangement. By opposition with the usual behaviour in intermetallics, light rare-earth compounds (R=Nd and Sm) have a lower ground state magnetization than the heavy rare-earth compounds (R=Gd-Tm). This manifests in their magnetocaloric response near the R ordering temperature: the compounds with R=Gd-Tm display a normal magnetocaloric effect of moderate magnitude (<50 mJ cm⁻³ K⁻¹ for a field variation of 5 T) while those with R=Nd and Sm present an inverse magnetocaloric effect of weaker magnitude. The potential interest of these phases for cooling applications is briefly discussed.     

Magnetic ordering in RCoSi2 (R = Tb, Dy, Ho) compounds

The crystal and magnetic structures of TbCoSi₂, DyCoSi₂ and HoCoSi₂ were studied by neutron diffraction using polycrystalline samples. At 4.2 K all three exhibit antiferromagnetic ordering: DyCoSi₂ and HoCoSi₂ of collinear. TbCoSi₂ of complex spiral types.     

Enhancement of magnetocaloric effects in La0.8R0.2(Fe0.919Co0.081)11.7 Al1.3 (R=Pr, Nd) compounds

The magnetic properties and magnetocaloric effects (MCEs) in La_0.8R_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 (R=Pr, Nd) compounds have been investigated. When Pr and Nd substitute for La, the Curie temperature of compounds decreases. The values of the MCEs are enhanced significantly by a partial substitution of Nd for La. Under the field change of 2 and 5 T, the maximum magnetic entropy changes for La_0.8Nd_0.2(Fe_0.919Co_0.081)_11.7Al_1.3 compound are −4.56 and −9.46 J/Kg K, respectively. It can be exploited for room temperature magnetic refrigeration material.     

Magnetic structures of R3Cu4Si4 (R=Dy, Ho and Er)

Polycrystalline samples of R₃Cu₄Si₄ (R=Dy, Ho, Er) intermetallics were studied with neutron diffraction methods. All of them crystallize in the orthorhombic structure of Gd₃Cu₄Ge₄-type and order antiferromagnetically at low temperatures. Magnetic moments localized at the rare earth atoms, that occupy two non-equivalent 2d and 4e sublattices, order simultaneously in Dy₃Cu₄Si₄. The order is described by the propagation vector accompanied by , δ=0.025(2). In Ho₃Cu₄Si₄ two propagation vectors are needed to model the magnetic order. These are: for the 4e sublattice, which disorders as the first when the temperature increases, and for the 2d sublattice. A similar situation is observed for Er₃Cu₄Si₄ where the propagation vectors are: k=(0,1−δ,0), δ=0.097(2) for the 4e sublattice, which disorders as the first with increasing temperature, and , δ=0.0015(6) for the 2d sublattice.     

Magnetic properties of some RPd2Si2 compounds (R=Gd,Tb, Dy,Ho and Er)

The magnetic susceptibility of the ternary compounds, RPd₂Si₂ (where R=Gd, Tb, Dy, Ho and Er) has been measured. GdPd₂Si₂ order antiferromagnetically at 13 and 20 K respectively; the rest of the compounds do not show clear ordering down to 4.2 K. Palladium carries no moment in these compounds. The De Gennes formula is not obeyed indicating that the exchange interaction between the 4f moments via conduction electrons is not isotropic     

Magnetic properties of the compounds R2Sc3Si4 (R=Gd, Tb, Dy, Ho, Er)

The magnetization of R₂Sc₃Si₄ compounds is measured in static magnetic fields up to 14 kOe in the temperature range 77–300 K. It is established that all compounds in the given series are paramagnetic at these temperatures. The paramagnetic Curie points are determined, and the effective magnetic moments are calculated. The measurements are performed on polycrystalline samples. Fiz. Tverd. Tela (St. Petersburg) 41, 1804–1805 (October 1999)     

Magnetic phase diagrams of R2RhIn8 (R = Tb, Dy, Ho, Er and Tm) compounds

We have grown and characterized single crystals of R(2)RhIn(8) (R=Tb, Dy, Ho, Er and Tm) compounds crystallizing in the tetragonal Ho(2)CoGa(8)-type crystal structure. Their magnetic properties were studied by specific heat and magnetization measurements. All the investigated compounds order antiferromagnetically with Néel temperatures of 43.6, 25.1, 10.9, 3.8 and 4.1 K, respectively. Magnetic phase diagrams were constructed.     

Magnetic characteristics of R6Mn23 hydrides (R = Gd,Ho or Er)

R₆Mn₂₃ systems, with R = Gd, Ho and Er, were hydrided to the composition R₆Mn₂₃H_x where x ap; 22. Magnetic properties of these systems and the parent intermetallics were studied over the temperature range 4 to 300 K and at applied field up to 21 kOe. Since Y₆Mn₂₃H₂₅ was established earlier to exhibit only Pauli paramagnetism, the magnetism of the R₆Mn₂₃ hydrides must originate with the rare earth sublattice. Gd₆Mn₂₃H₂₂ orders at ≈ 150 K, whereas ordering in Gd₆Mn₂₃ occurs at 468 K. The moment measured at 4 K indicates a non-collinear structure, perhaps generated by competition involving exchange between nearest and next nearest neighbors. The hydrides involving Ho and Er appear to remain paramagnetic to the lowest temperatures studied, perhaps because the reduced de Gennes factor exchange is insufficient to produce magnetic ordering. The possibility cannot be excluded, however, that they are antiferromagnetic.     

RCo10Mo2(R=Y,Ho)化合物的磁性研究

利用SQUID磁强计和脉冲强磁场设备对RCo₁₀Mo₂(R=Y,Ho)化合物的磁性进行了研究.单个晶格模型和双子晶格模型和双子晶格模型被分别用于解释取向样品的磁化过程,稀土次晶格和过渡金属次晶格的各向异性以及它们之间的相互作用由此得到了较好的描述. 关键词：     

Electronic and magnetic properties of the rare earth intermetallic compounds RRu4Sn6 (R=Nd, Sm, Gd, Tb, Dy and Ho)

A number of compounds of structural formula RRu₄Sn₆ (R=rare-earth element) have previously been reported to form in the tetragonal crystal structure with space group I4¯2m. In this structure the R atoms are well isolated from each other. We embarked on this study to investigate the physical properties and to compare with earlier results obtained on the strongly correlated, low charge-carrier density compound CeRu₄Sn₆. Here we report our results of crystallographic, electrical resistivity, and magnetic studies on this family of compounds. In contrast to the behaviour in CeRu₄Sn₆, magnetic ordering is evident at low temperatures in the compounds with R=Sm, Gd, and Dy, as is evidenced by well-resolved anomalies in the temperature dependence of the electrical resistivity and static magnetic susceptibility.     

Magnetic susceptibility measurements for some of the intermetallic compounds R2Pt (R = Gd,Tb, Dy,Ho, Er)

The magnetic properties of some of the intermetallic compounds R₂Pt have been studied by means of susceptibility measurements. The compounds are probably ferrimagnetic or they possess some noncollinear structure. With the exception of Gd₂Pt two magnetic transitions with temperature are observed. At 4.2 K the magnetization of Tb₂Pt shows appreciable hysteresis. In the paramagnetic region the compounds confirm the free ion picture of the R³⁺ except for Gd₂Pt which is still in a nonparamagnetic state even at 300 K.     

Magnetic properties and hyperfine interactions in RCo2B2 (R = Nd,Gd, Tb)

The magnetic properties of RCo₂B₂ compounds which crystallize in the ThCr₂Si₂ structure with R = Nd, Gd, Tb have been investigated. The magnetic structure is ferromagnetic for NdCo₂B₂ and GdCo₂B₂, T_c equals 32 and 26 K respectively and antiferromagnetic for TbCo₂B₂ (T_N = 19 K). Curie-Weiss behaviour is exhibited by all the compounds and the effective moments derived indicate that Co is diamagnetic. The difference in magnetic properties between RCo₂B₂ and other isomorphous RCo₂X₂ (X = Si, Ge) is discussed. Mössbauer studies of ¹⁵⁵Gd in GdCo₂B₂ yielded the hyperfine interaction parameters and determined the direction of the magnetization to be in the basal plane. The electric quadropole interaction at 4.1 K is 580 MHz sec^?1, this is the largest ever found in an intermetallic Gd containing compound.     

Magnetic properties and structure of hydrogen-amorphized intermetallic compounds RFe2Hx (R=Y, Gd, Tb, Dy, Ho, Er)

The magnetic properties and structure of hydrogen-amorphized RFe₂H_x compounds (R=Y, Gd, Tb, Dy, Ho, Er) have been studied. It is shown that amorphization of the RFe₂H_x hydrides results in an increase of Fe-Fe, and a decrease of R-Fe exchange interaction energy compared to their crystalline hydride counterparts. The magnetic structure of amorphous RFe₂H_x compounds, with the exception of those with R=Y and Gd is apparently noncollinear ferrimagnetic, as in the crystalline hydrides. A model of the heterophase state of amorphous RFe₂H_x hydrides based on x-ray diffraction and magnetic data is proposed. Fiz. Tverd. Tela (St. Petersburg) 39, 908–912 (May 1997)     

Magnetic phase transitions in RMnGe (R=Tb, Dy) compounds induced by high magnetic fields

Magnetization isotherms for polycrystalline TbMnGe and DyMnGe compounds were measured at the temperature 4.2 K in pulsed magnetic fields (up to 360 kOe). The received isotherms demonstrate the appearance of metamagnetic transitions at low temperatures. Both compounds crystallize in the orthorhombic TiNiSi-type structure. It was found that the magnetic phase transitions with a destruction of ferrimagnetic spiral structure occur in the TbMnGe and DyMnGe compounds in high magnetic fields. An attempt was undertaken to explain the nature of these transitions using the results of the powder neutron diffraction and the qualitative estimation of the exchange interaction values on the basis of the molecular field theory.     

The magnetic properties and magnetocaloric effects in binary R-T(R = Pr,Gd,Tb,Dy,Ho,Er,Tm;T = Ga,Ni,Co,Cu)intermetallic compounds

In this paper, we review the magnetic properties and magnetocaloric effects(MCE) of binary R–T(R = Pr, Gd, Tb,Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series, R_(12)Co_7 series, R_3 Co series and RCu_2series), which have been investigated in detail in the past several years. The R–T compounds are studied by means of magnetic measurements, heat capacity measurements, magnetoresistance measurements and neutron powder diffraction measurements. The R–T compounds show complex magnetic transitions and interesting magnetic properties.The types of magnetic transitions are investigated and confirmed in detail by multiple approaches. Especially, most of the R–T compounds undergo more than one magnetic transition, which has significant impact on the magnetocaloric effect of R–T compounds. The MCE of R–T compounds are calculated by different ways and the special shapes of MCE peaks for different compounds are investigated and discussed in detail. To improve the MCE performance of R–T compounds,atoms with large spin(S) and atoms with large total angular momentum(J) are introduced to substitute the related rare earth atoms. With the atom substitution, the maximum of magnetic entropy change(?SM), refrigerant temperature width(Twidth)or refrigerant capacity(RC) is enlarged for some R–T compounds. In the low temperature range, binary R–T(R = Pr, Gd,Tb, Dy, Ho, Er, Tm; T = Ga, Ni, Co, Cu) intermetallic compounds(including RGa series, RNi series,R_(12)Co_7 series, R_3 Co series and RCu_2series) show excellent performance of MCE, indicating the potential application for gas liquefaction in the future.     

Magnetic properties of R2Pt compounds with R = Gd,Tb, Dy,Ho, Er and Tm

Magnetic properties of polycrystalline samples of R₂Pt compounds (R = Gd, Tb, Dy, Ho, Er and Tm) are presented. The Gd, Td, Dy, Ho based compounds are ferromagnetic with Curie temperatures ranging between 155 and 17 K. Er₂Pt and Tm₂Pt are antiferromagnetic with Néel temperatures of 9 and 5 K respectively. The observed properties are discussed considering indirect exchange interactions and crystal field effects acting on the rare earth ions which lies in very low symmetry sites.     

Electronic structure and bonding properties for Laves-phase RV2 (R=Ti, Nb, Hf, and Ta) compounds

The electronic structure and bonding properties of Laves-phase compounds RV₂ (R=Ti, Nb, Hf, and Ta) with C15 structure have been investigated using the full-potential linearized augmented plane-wave method. The results show that the chemical bonding is metallic–ionic–covalent in nature in these compounds, and the covalent bonding between V and V atoms strengthens with the atomic number, increasing among the RV₂ (R=Ti, Nb, Hf, and Ta) compounds. The density of states (DOS), equilibrium volume, and elastic properties are discussed, which is important for understanding the physical properties of RV₂ (R=Ti, Nb, Hf, and Ta) and may inspire future experimental research.     

Structure and magnetostriction of RFex (1.6 x 2.0) and R(Fe1−yTiy)1.8 (y 0.2) alloys (R=Dy0.65Tb0.25Pr0.1)

Structure, Curie temperature and magnetostriction of RFe_x (1.6 x 2.0) and R(Fe_1−yTi_y)_1.8 (y 0.2) alloys (R=Dy_0.65Tb_0.25Pr_0.1) have been investigated using optical microscopy, X-ray diffraction, AC initial susceptibility and standard strain gauge techniques. The homogenized RFe_x alloys are found to be essentially single phase in the range of 1.8 x 1.85. The second phase is a rare-earth-rich phase when x 1.8, and (Dy, Tb, Pr)Fe₃ phase when x 1.85. X-ray diffraction indicates that the R(Fe_1−yTi_y)_1.8 alloys contain a small amount of Fe₂Ti phase when y 0.05, which increases with the increment of Ti content. The Curie temperature of R(Fe₁−_yTi_y)_1.8 alloys slightly enhances with increasing Ti concentration when y 0.05, then remains almost unchanged in the range of 0.05 y 0.20. The magnetostriction of RFe_x alloys is improved when x 1.80 and reduced by increasing Fe content when x 1.85. The magnetostriction of R(Fe_1−yTi_y)_1.8 alloys is lowered by increasing Ti content.