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 anisotropy in Fe/rare‐earth multilayers

Magnetic anisotropy of Fe/RE multilayers (RE=Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) was studied using ⁵⁷Fe Mössbauer spectroscopy. Perpendicular magnetic anisotropy was observed in Fe/Pr, Fe/Nd, Fe/Tb, and Fe/Dy multilayers. The external field dependence of the direction of magnetic moments was also examined for Fe/Tb multilayers. The results imply that the perpendicular magnetic anisotropy originates from the single ionic anisotropy of RE at the interfaces.     

Susceptibilite magnetique des composes ternaires TCu2Ge2(T = Gd,Tb,Dy,Ho,Er,Tm)

Susceptibility measurements are performed on the tetragonal TCu₂Ge₂ ternary compounds in the temperature range 4.2–200 K under a constant magnetic field of 5 KOe. The compounds with T = Gd,Tb,Dy and Ho are antiferromagnetic with Néel temperatures 12,15,8 and 6.4 K respectively. The compounds with T=Er and Tm do not show any ordering temperature down to 4.2 K. The temperature dependence of the reciprocal susceptibility of all compounds follows a Curie-Weiss law. The paramagnetic Curie temperatures for all compounds are negative.     

On the origin of the perpendicular anisotropy in rare earth-transition metal amorphous films

The induced anisotropy in amorphous (Co₉₃Zr₇)_100−x(RE)_x films has been studied. The sputter deposition was performed in a magnetic field. For RE = Nd, Pr, Dy and Tb, the formation of a well-defined in-plane uniaxial anisotropy K_u is related to the single-ion anisotropy of RE atoms. When RE = Gd and Sm, a biaxial anisotropy develops, comprising K_u and a perpendicular anisotropy K_p. This magnetic structure is expected to be related to the simultaneous formation of two distinct local structural configurations when the deposition temperature is higher than the critical value.     

Susceptibility measurements on some R5In3 compounds

The magnetic susceptibility of some rare earth-indium compounds has been measured in the temperature range 4.2–300 K under a constant field of 1 kOe. The compounds with R = Gd, Tb and Dy are antiferromagnetic, having Néel temperatures between 4.2 and 78 K ; those with R = Ho, Er and Tm seem to be ferromagnetic with ordering temperatures probably below 4.2 K. Y₅In₃ presents a temperature independent susceptibility.     

Rare earth single-ion anisotropy and the magnetic structures of the RTiO3 perovskites: R = Tb,Dy, Ho,Er and Tm

Attention is drawn to common features in the magnetic structures of the isostructural RMO₃ phases where R = Tb, Dy, Ho, Er and Tm and M = Al, Ti, Cr, Fe and Co. The orientation of the rare earth magnetic moment with respect to the orthorhombic c-axis depends only on R. For R = Er and Tm the moments are parallel to the c-axis while for R = Tb, Dy and Ho they lie in the a-b plane. The in-plane moments are canted with respect to the a and b axes with both ferromagnetic and antiferromagnetic components and the canting angles are constant for a given R independent of M. Using symmetry arguments we show that the above systematics can be understood in terms of the rare earth single-ion anisotropy. Detailed calculations incorporating a crystal field of C_s symmetry determined for Er³⁺ in YAlO₃ and an isotropic molecular field of magnitude appropriate to the RTiO₃ compounds produce results in agreement with the experimental observations. Essentially the same results are obtained for a crystal field of D_4h symmetry. The B²₀O²₀ term in the crystal field Hamiltonian is identified as the factor which determines the orientation of the rare earth moment.     

Magnetic properties of ternary gallides of type RNi4Ga (R=rare earths)

The magnetic properties of RNi₄Ga (R=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu) compounds have been investigated. These compounds form in a hexagonal CaCu₅ type structure with a space group P6/mmm. Compounds with the magnetic rare earths, R= Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm, undergo a ferromagnetic transition at 5, 17, 20, 19, 12, 3.5, 8 and 6.5 K, respectively. The transition temperatures are smaller compared to their respective parent compounds RNi₅. PrNi₄Ga is paramagnetic down to 2 K. LaNi₄Ga and LuNi₄Ga are Pauli paramagnets. All the compounds show thermomagnetic irreversibility in the magnetically ordered state except GdNi₄Ga.     

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.     

Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Huge magnetocrystalline anisotropy in cubic rare earth-Fe2 compounds

Magnetization and magnetic anisotropy measurements were made on single crystals of ErFe₂ from 77°K to room temperature. The magnetic anisotropy is much larger than any previously reported for cubic metals. Based upon these measurements the magnetic anisotropies of the Laves phase RFe₂ compounds (R = Tb, Dy, Ho and Tm) were predicted.     

STRUCTURE AND MAGNETIC PROPERTIES OF LaCo13-BASED ALLOYS

The structure and magnetic properties of two series of LaCois-based alloys, LaCo_13-xFe_x(0≤x≤6) and La_1-xR_x(Co, Fe)₁₃ (x=0.1,0.2; R=Y, Ge, Pr, Nd Sm, Gd, Tb, Dy, Ho, Er, and Yb), are studied by X-ray diffraction and magnetic mea- surements. In the above-mentioned composotions, all the samples display a structure of NaZn₁₃ type (space group: Fm3c). In LaCo_13-xFe_x system, as the iron content increases, its Curie temperature decreases, while thc magnetic moment per 3d atom increases. This may be explained by a rigid band model. In the other alloy system, the Curie temperature goes through a maxium at R=Gd, and this reflects the influ- ence of R - T interaction. It is also observed that saturation magnetization varies with R and gets lower when R is a heavy rare earth element. The contribution of R is close to that of a free-ion moment. La_0.9Pr_0.1Co₉Fe₄ has the largest value 29μ_B/f.u.     

MAGNETIC PROPERTIES OF NEW SERIES R-Mo-Fe NITRIDES WITH THE ThMn12-TYPE STRUCTURE AT A LOWER Mo CONTENT

A systematic study has been made on formation condition, crystallographic structure and magnetic properties of RMo_1.5Fe_10.5N_x, where R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er. The interstitial nitrogen atom effects on Curie temperature, saturation magnetization and magneto-crystalline anisotropy have been investigated. Two important preliminary results have been obtained. (1) A single phase crystallized in the ThMn₁₂-type structure was stabilized with a smaller content of molybdenum, thus, the compounds possess a higher Curie temperature and a larger spontaneous magnetization. (2) A complete system of compounds with 1:12 type structure containing the light rare earth cerium and praseodymium was synthesized, which will be favorable for developing new rare earth hard magnetic materials.     

Magnetic properties of ternary rare-earth compounds of the type R2Fe14B

Ternary tetragonal compounds of the composition R₂Fe₁₄B were observed for R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The lattice constants and the X-ray density of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 20 T. These latter measurements were made in two mutually perpendicular directions, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy was found to consist of contributions due to the Fe and rare-earth sublattice, respectively.     

Magnetic and superconducting properties of rare earth osmium stannides

We present data on the magnetic and superconducting properties of rare earth osmium stannides. The compounds of Tb and Ho are superconducting only, those of Er and Tm are reentrant superconductors, and those of Gd and Dy appear to exhibit some type of short range magnetic order at low temperatures.     

An57Fe Mössbauer study of rare-earth intermetallic compounds R(Fe11Ti)

⁵⁷Fe Mössbauer spectra are reported for the ThMn₁₂ structure series of intermetallic compounds R(Fe₁₁Ti) (R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu). The Mössbauer spectroscopy of oriented absorbers has been used to study the spin reorientation transitions exhibited by the members of the series where the second-order Stevens coefficient α_J of the rare-earth (Nd, Tb and Dy) is negative. A simple model has been established to deduce the canting angle from the Mössbauer spectra of oriented absorbers. The results are analyzed in terms of a crystal-field model. The crystal field parameters must be increased significantly to account for the observed large anisotropy in the Sm(Fe₁₁Ti) compound, which may find applications as a permanent magnet.     

Order parameters and phase diagram of multiferroic RMn2O5

The generic magnetic phase diagram of multiferroic RMn2O5 (with R=Y, Ho, Tb, Er, Tm), which allows different sequences of ordered magnetic structures for different R's and different control parameters, is described using order parameters which explicitly incorporate the magnetic symmetry. A phenomenological magnetoelectric coupling is used to explain why some of these magnetic phases are also ferroelectric. Several new experiments, which can test this theory, are proposed.     

Structural relative stabilities and pressure-induced phase transitions for lanthanide trihydrides REH3 (RE=Sm,Gd, Tb,Dy, Ho,Er, Tm,and Lu)

The structures, structural relative stabilities, pressure-induced phase transitions, and equations of state for lanthanide trihydrides REH₃ (RE=Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) are systematically studied using ab initio calculations under a core state model (CSM). The obtained ground-state parameters, such as lattice constants and bulk modulus, agree well with the available data. Among the P6₃/mm, P3?c1, and P6₃cm structures, the P6₃cm structure is found to be the most stable structure for lanthanide trihydride via the comparison of the calculated total energies. With the help of Birch–Murnaghan equation of state, the structural transitions from hexagonal to cubic for REH₃ (RE=Sm, Gd, Ho, Er, and Lu) under pressure are affirmed; especially, the similar behavior of REH₃ (RE= Tb, Dy, and Tm) is reasonably predicted for the first time by this means. For the transitions, the repulsive interactions of H–H atoms may play an important role in terms of the analysis of the structures in the vicinity of the theoretical phase transition.     

Magnetic and structural studies of the alloy system REIn0.5Ag0.5

The structural and magnetic properties of the alloy system REIn_0.5Ag_0.5 [RE = Gd, Tb, Dy, Ho, Er, Tm and Yb] are reported. All these alloys (except that of Yb) crystallize in a cubic CsCl type structure at room temperature. Low temperature X-ray diffraction data does not reveal any structural phase transformation down to 8 K. On the basis of magnetic susceptibility data at a different temperature (3–300 K) and applied magnetic field (2 × 10⁵ to 8 × 10⁶ A m^-1, it has been concluded that GdIn_0.5Ag_0.5 is ferromagnetic (T_c = 118 K), TbIn_0.5Ag_0.5 and DyIn_0.5Ag_0.5 are meta magnetic (T_N = 66 and 30 K, respectively) and alloys involving Ho, Er, Tm and Yb are ferrimagnetic with Néel temperatures (T_N) equal to 24, 22, 21 and 20 K, respectively. The evaluated effective magneton number (p) is found to be slightly larger compared to theoretical values for tripositive ions of Gd, Tb and Dy and a bit smaller for Ho, Er, Tm and Yb. The results have been qualitatively explained using appropriate theories.     

The Magnetic Hyperfine Field of 111Cd in the Rare Earth–Nickel Laves Phases RNi2

The magnetic hyperfine field of ¹¹¹Cd in the C15 Laves phases RNi₂ has been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature for the rare earth constituents R = Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm.     

The magnetic hyperfine field at Cd nuclei in the rare earth ferromagnets Gd,Tb, Dy,Ho, Er and Tm

The time differential perturbed angular correlation technique has been used to study the combined magnetic and electric hyperfine interactions at the site of a¹¹¹Cd impurity in the rare earth ferromagnets Gd, Tb, Dy, Ho, Er, and Tm at 4.2 °K. The following magnetic hyperfine fields at the site of¹¹¹Cd have been found: ¦H _hf ¦=340(7) kG in Gd, 275 (5) kG in Tb, 221 (4) kG in Dy, 116 (3) kG in Er and 60 (6) kG in Tm. In Ho two magnetically different sites were observed with magnetic fields of 159 (3) and 139 (3) kG. Both sites are equally populated. The coupling constantJ _5f of the conduction electron-4f interaction has been calculated for the different rare earth metals from the measured hyperfine fields by means of the RKKY theory.