V. U. S. Rao

Magnetic properties of RMn2Ge2 compounds (R=La, Ce, Pr, Nd, Cd, Tb, Dy, Ho, Er, and Th)

Magnetic properties RMn2Ge2 compounds where R is La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, and Th have been investigated from 4.2 to 500 K. LaMn2Ge2, CeMn2Ge2, PrMn2Ge2, and NdMn2Ge2 are ferromagnetic with Curie temperatures of 306, 316, 334, and 334 K, respectively. The heavy rare‐earth compounds do not order ferromagnetically until low temperatures. GdMn2Ge2 shows a sharp magnetic transition at 97 K both in the magnetization‐vs‐temperature and resistivity‐vs‐temperature data. For this compound, it is proposed that above 97 K the Mn moments order antiferromagnetically among themselves while the Gd moments are disordered. Below 97 K the Mn moments couple ferromagnetically with each other but are opposed to the ordered Gd sublattice. Magnetic moment obtained at 4.2 K can be explained for all the compounds on the basis of an antiferromagnetic coupling between Mn and rare‐earth spins.

Thermal, magnetic and electrical characteristics of PrNi5

Abstract Results of measurements of the heat capacity, magnetic susceptibility and electrical resistivity of PrNi5 are presented for temperatures ranging from 2 to 300°K. Magnetization of PrNi5 goes through a maximum at about 16°K. Heat capacity measurements fail to show a λ-type thermal anomaly peaking at 16°K, indicating that this is not a Neel point. The difference between the heat capacity of PrNi5 and non-magnetic LaNi5 is Schottky-type with two maxima, at 16° and 58°K. The maxima in Cp and magnetization are consequences of the crystal field interaction, which leads to Van Vleck paramagnetism in this material at low temperatures. A reasonably successful analysis of the heat capacity and susceptibility results was made using the Hamiltonian, ℋ = g μ B J ⋅ H + W 246 { ( 1 − | y | ) O 2 F 2 + y [ x O 4 F 4 + ( 1 − | x | ) O 6 F 6 ] } . Resistivity measurements on NdNi5 show a sharp drop at its Curie point, which is ascribed to the loss of its spin-disorder resistivity. No such effect is observed for PrNi5. The analysis indicates that the decline in resistivity for the latter material is so small and so gradual as to be experimentally imperceptible, this being a consequence of the development of Van Vleck paramagnetism rather than magnetic ordering in PrNi5 at reduced temperatures. The observed magnetic entropy of PrNi5 is consistent with other observations which indicate that the ground state for Pr+3 in PrNi5 is a singlet.

Magnetic and Electrical Characteristics of REPd3 Intermetallic Compounds

Magnetic characteristics of 12 REPd3 (RE = a rare earth) compounds have been studied between 4° and 300°K. Electrical resistivity measurements have been made on the Ce, Gd, and Ho compounds. All compounds are paramagnetic at room temperature; all except CdPd3, SmPd3, and EuPd3 exhibit Curie‐Weiss behavior with paramagnetic moments in close agreement with that expected for the free tripositive ion. The susceptibility behavior of CePd3 is ascribed to the Kondo phenomenon (spin compensation) while that of SmPd3 and EuPd3 to the narrowness of the multiplet spacings. This interpretation for CePd3 is supported by its resistivity‐temperature behavior. Evidence for magnetic ordering is found only for GdPd3, which seems to order ferromagnetically below 7°K.

Magnetic properties of pseudo‐ternaries of the composition Nd(Mn1−xCrx)2Si2

Structural and magnetic properties of a number of pseudo‐ternaries of the composition Nd(Mn1−xCrx)2Si2 have been examined. In the composition range 0<x<0.6 they crystallize in tetragonal BaAl4‐type structure. Magnetic properties were examined between 4.2 K and 400 K in applied fields up to 20 kOe. NdMn2Si2 exhibits anomalies in the magnetization versus temperature plots at about 40 K and 380 K—the former due to the ordering of the rare earth moments and the latter due to the ordering of the transition metal sublattice. Addition of chromium to this compound increases the crystal cell volume significantly and modifies the magnetic behavior. The transition metal sublattice orders antiferromagnetically at 380 K, 260 K and 200 K for compositions of X=0, 0.2 and 0.3, respectively. Compounds of the composition X=0.2, 0.3 and 0.4 exhibit unusual thermomagnetic hystereses. The thermomagnetic curves for these compositions in low external fields (<10 kOe) exhibit an increase in the magnetization upon warming the sam...

Magnetic properties of RMn2X2 compounds (R=Rare earth, Y or Th and X=Ge, Si)

Magnetic properties of RMn2Ged2 and RMn2Si2 compounds crystallizing in th BaAl4 type structure have been investigated over a wide temperature range (4.2 K to 1200 K). LaMn2Ge2, CeMn2Ge2, PrMn2Ge2, NdMn2Ge2 and LaMn2Si2 all possess Curie temperatures above 300 K and the easy direction of magnetization have been found to be along the c‐axis. When R is a heavy rare earth antiferromagnetic coupling was obtained at 4.2 K between the rare earth and manganese moments whereas when R is a light rare earth a ferromagnetic coupling of moments was obtained. Ymn2Si2, ThMn2Si2 and ThMn2Ge2 possess a small moment <⋅2μB at 4.2 K. High temperature susceptibilities on RMn2Si2 compounds indicate a Curie‐Weiss behavior.

Influence of the crystalline electric field on the Kondo resistivity of CexLa1−xPd3 ternaries

Abstract The electrical resistivities of the cubic Ce x La 1− x Pd 3 ternary alloys have been measured from 2° to 300° K. The alloys were found to consist of single phases except in the region 0·3 x

Temperature compensated magnetic materials of the type SmxR1−xCo5 (R=Tb,Dy,Er)

Permanent magnets made from SmCo5 exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04% per deg. C. between −100 and +200 C. It is desirable to improve this property by suitable substitutions. In the present study, a systematic examination of the preparation, structural and magnetic characterization of SmxR1−xCo5 (R=Tb, Dy and Er) has been undertaken. The ternaries were prepared by induction melting of the metals of proper stoichiometries. Magnetic studies were performed between 4.2 and 1000 K in applied fields up to 20 kOe. The results indicate that the best temperature compensation is achieved in the ternary SmxDy1−xCo5. Saturation magnetization and Curie temperatures are also reported.Permanent magnets made from SmCo5 exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04% per deg. C. between −100 and +200 C. It is desirable to improve this property by suitable substitutions. In the present study, a systematic examination of the preparation, structural and magnetic characterization of SmxR1−xCo5 (R=Tb, Dy and Er) has been undertaken. The ternaries were prepared by induction melting of the metals of proper stoichiometries. Magnetic studies were performed between 4.2 and 1000 K in applied fields up to 20 kOe. The results indicate that the best temperature compensation is achieved in the ternary SmxDy1−xCo5. Saturation magnetization and Curie temperatures are also reported.

Superconductivity of the hydrides and deuterides of Hf0.5Zr0.5V2

Abstract The superconducting transition temperature of Hf 0.5 Zr 0.5 V 2 was enhanced by 1.7 K upon a small addition of H into the lattice. The maximum T c of 11.8 K occurs at the composition Hf 0.5 Zr 0.5 V 2 H 0.5 . A large “normal” isotope effect was observed with respect to the deuteride.

Crystal field effects on the magnetocrystalline anisotropy in HoAl2

Abstract Recent work on the heat capacity of HoAl 2 revealed an anomaly at 20°K, the origin of which was not understood. It is now suggested that this anomaly originates from a change in the easy direction of magnetization brought about by a combined effect of crystalline electric field and exchange field. Calculations by the equivalent operator method have been performed employing reasonable combinations of crystal field parameters. The exchange field acting on Ho 3+ is determined in a self-consistent manner. Results are presented to illustrate the expected occurrence of a change in the easy direction of magnetization for a range of crystal field parameters which are compatible with those found for other R Al 2 compounds. The magnetic moment on Ho 3+ ion calculated on the basis of this model is in agreement with experiment.

Heat capacities and related thermal properties of DyNi5, HoNi5 and ErNi5 between 5 and 300 K☆

Abstract Heat capacity data and calculated thermodynamic functions are presented for DyNi 5 , HoNi 5 and ErNi 5 . λ-type thermal anomalies are noted at 12.0 K (DyNi 5 ), 4.1 K (HoNi 5 ) and 8.0 K (ErNi 5 ). Schottky-type anomalies are observed at higher temperatures. The λ and Schottky anomalies are ascribed to the destruction of ferromagnetic order and to crystal field excitation, respectively. A deficiency of magnetic entropy, compared to R ln(2 J + 1), is noted corresponding roughly to R ln2. This suggests that the ground state in the ordered materials is a doublet. ErNi 5 is analyzed using a Hamiltonian containing terms representing the crystal field and magnetic interactions. The analysis shows that a doublet ground state can result with reasonable values of the crystal field parameters. The parameters are shown to be consistent with the heat capacity behavior of ErNi 5 . Ordering temperatures are not proportional to the de Gennes function.