Yasushi Amako

Pressure-Induced Valence Transition and Heavy Fermion State in Eu2Ni3Ge5 and EuRhSi3

We succeeded in growing single crystals of Eu2Ni3Ge5 and EuRhSi3 by the In-flux method, and measured the electrical resistivity under pressures. Both compounds are Eu-divalent antiferromagnets with the Neel temperatures TN = 18.6 and 47.7 K, respectively. With increasing pressure, the resistivity in Eu2Ni3Ge5 indicates a clear kink at Tv = 220 K under 8.0 GPa, for example, which corresponds to a valence transition. The valence of Eu ions deviates from divalence toward trivalence. Correspondingly, antiferromagnetic ordering disappears completely. The low-temperature resistivity is, surprisingly, very similar to the resistivity of a well-known heavy fermion superconductor CeCu2Si2, possessing a two-peak-structure based on the Kondo effect. In fact, the A value of the resistivity ρ = ρ0 + AT2 in the Fermi liquid relation becomes large, A = 0.3 µΩ·cm/K2 at 8.0 GPa. The similar characteristic features are observed in another compound EuRhSi3.

Magnetic properties of the hypothetical compound YFe5

Abstract The magnetic properties of the hypothetical compound YFe5 are obtained by extrapolating the values of lattice constants, saturation magnetizations, Ms, and 57 Fe hyperfine fields, Beff, for Y(T1−xFex)5 (T=Co and Ni). For the hypothetical compound YFe5, the average Fe moment and 57 Fe hyperfine fields are almost consistent with the estimated values based on an interpolation of the concentration dependence of the Y–Fe compounds assuming that the values of Ms and the average Beff show a maximum at x=0.7 and 0.81, respectively.

The119Sn Mössbauer effect in RMn6Sn6 compounds (R=Gd,Y)

The magnetic properties of intermetallic compounds RMn6Sn6 (T=Gd and Y) have been investigated by119Sn Mössbauer effect measurements. The differences of the hyperfine field on both the Sn1 and Sn3 sites were small between GdMn6Sn6 and YMn6Sn6, while the Mn sublattice orders ferromagnetically for R=Gd and antiferromagnetically for R=Y. This result indicated that Mn moments order antiferromagnetically in the intra-plane of the Kagomè net in YMn6Sn6.

Magnetic properties of RFe12−xMox compounds with R=Y, Gd, Ho, Er versus the molybdenum content

Abstract Magnetic properties of the tetragonal RFe 12− x Mo x compounds with R=Y, Gd, Ho, Er and for x ranging from one to three have been analysed. For compounds with Curie temperatures larger than room temperature (RT), measurements were performed on oriented powders allowing an estimate both of the easy magnetisation direction and of the magnetocrystalline anisotropy. The Fe anisotropy always favours the c -axis whereas rare earth anisotropy depends on the sign of second order Stevens factor favouring the c -axis for Ho and the basal plane for Er. Then in the latter compound spin reorientations are observed at temperatures which increase with x . In these ferrimagnetic compounds the Fe sublattice magnetisation prevails over that of the rare earth sublattice except for R=Er and x =2.5 where a compensation temperature is observed. Analysis of the Curie temperatures allows an estimate of the R–Fe and Fe–Fe exchange interactions in the different compounds. They are comparable to those determined in other 1–12 compounds and tend to increase with the Fe amount as observed in a large number of rare earth-3d transition metal materials.

Magnetic properties of R3Co (R=Gd, Tb, Dy, Ho, Er)

Abstract The magnetic properties of R 3 Co compounds have been studied by the magnetization, electrical resistivity and NMR measurements. The magnetic ordering temperatures were obtained from the electrical resistivity measurement. The complex magnetic susceptibilities were explained by the metamagnetic transition under an applied field.

Magnetic properties of RMn12 (R=rare earth)

Abstract Magnetic properties of RMn 12 (R Gd, Tb) intermetallic compounds were studied by NMR and magnetization measurements. The 8f Mn sites in TbMn 12 were divided into two different magnetic sites below T c .

Magnetic properties of single crystal Y3(Fe0.93V0.07)29

Abstract We have successfully prepared a Y 3 (Fe 0.93 V 0.07 ) 29 single crystal by the Czochralski method followed by an appropriate annealing procedure. The spontaneous magnetization lies in the (1 0 2)-plane over the investigated temperature range of 5–300 K. The Curie temperature is T c = 439 K. The saturation magnetization at 5 K is M s = 48.3 μ B /f.u. which corresponds to an average Fe magnetic moment of 1.79 μ B . The uniaxial anisotropy K 1 * of Fe-sublattice at T = 5 K is — 2.25 MJ/m 3 . We observed no easy magnetization direction within the (1 0 2)-plane which may be due to the coexistence of Y 3 (Fe,V) 29 crystallites, oriented to each other at a relative angle of θ = 60° about the [1 0 2] axis. This feature has been well explained with a six-domain model in terms of the anisotropy constants K i ( T ) of the iron sublattice of the monoclinic 3 : 29 structure.

NMR Study of R2Co7B3 (R=Y, Ce, Nd, Sm and Gd) Compounds

In order to study the magnetic properties of the Co-sublattice of R2Co7B3, the 59Co NMR and magnetic measurements have been carried out at 4.2 K. The R2Co7B3 (R=Y, Ce, Nd, Sm and Gd) compounds with a hexagonal Ce2Co7B3-type structure are obtained. The Co moments at the 6i1 site are estimated from NMR and are found to be nearly consistent with those obtained from the magnetic measurements for R=Y, Sm and Gd. On comparing the calculated moments per unit cell, µ, with the saturation magnetization, Ms, for R=Y and Gd, the values of µ are found to be very consistent with those of Ms and the value of µ for R=Ce is much larger than that of Ms.

The anomalous behaviour of the electrical resistivities of Gd(Fe,Mn)2 and Gd6(Fe,Mn)23

Abstract We have measured the electrical resistivities to investigate the behaviours of the excess Gd atoms in the structure change of Gd(Fe,Mn) 2 to Th 6 Mn 23 , comparing to those of Gd 6 (Fe,Mn) 23 with Th 6 Mn 23 -type. The results suggest that the excess Gd atoms exist in a metallic state and behave to be non-magnetic.

Nuclear magnetic resonance of CeCo4B

Abstract The 50 Co hyperfine fields at the 2c and 6i sites in CeCo 4 B have been determined as +2.5 and −32kOe , respectively, by extrapolating 59 Co resonance fields to zero external field. The orbital contribution to Co moments at each site was estimated.