G.F. Zhou

Magnetic interactions in R2Fe17−xAlx compounds ( R = Ho, Y)

Abstract The temperature and field dependence at 4.2 K of the magnetization of Y2Fe17−xAlx and Ho2Fe17−xAlx ( x ≤ 10) compounds has been studied. Coupling constants have been derived by analyzing both the temperature dependence and the field dependence of the magnetization with a mean-field model. The results are compared to each other. The influence of the Ho-Ho interaction is considered. There is no pronounced temperature dependence of the interaction constant between the rare-earth and transition-metal sublattice.

Magnetic behaviour of Al and Mn substituted Gd2Fe17 compounds

Abstract We investigated the magnetic properties of Gd 2 Fe 17− x M x compounds with M=Al or Mn. We performed low-field magnetization measurements to obtain values for the Curie temperature and high-field magnetization measurements ( B ≤38T) on powdered samples that were free to orient themselves in the field applied to obtain values for the saturation magnetization. From the high-field slope of the magnetization we derived values for the R–T coupling constants n RT using the mean-field approximation. We find that substitution of Al or Mn, although it reduces the Fe magnetization in different ways, has only little influence on the intersublattice coupling strength.

Magnetic properties of ThMn12-type RCo12−xVx compounds with R = Y, Gd, Tb, Dy, Ho, Er

Abstract Polycrystalline specimens of stoichometric RCo 12− x V x (with R = Y, Gd, Tb, Dy, Ho, Er) have been prepared and investigated by x -ray diffraction. Specimens with 2≤ x ≤3 were fpund to be approximately single phase (ThMn 12 -type structure), and used for measurement of the magnetisation, both as a function of temperature and as a function of applied magnetic fields up to 35 T at 4.2 K. From the magnetisation measurements values for the Curie temperatures and Co moments were estimated, and found to be much lower than in most R-Co intermetallics. For the compounds with a magnetic R component, values for the J RT coupling constants were derived. The determined J RT values decrease with increasing atomic number of the rare-earth component.

Intersublattice interactions in R2Fe17−xAlx compounds (R=Tb, Dy, Er and Tm)

Abstract The field dependence of the magnetization at 4.2 K was studied in fields up to 35 T for the pseudobinary compounds R2Fe17−xAlx (R = Tb, Dy, Er and Tm). Values for the intersublattice-coupling strength were derived from a mean-field analysis of the magnetic isotherms. For the series Dy2Fe17−xAlx we determined the concentration dependence of the Curie temperature and the compensation temperature. A magnetic phase diagram for this series has been constructed.

Magnetic coupling in rare-earth compounds of the type RCo12B6

Abstract The field dependence (up to 35 T) of the magnetization at 4.2 K of several compounds of the type R1−xYxCo12B6 has been studied. The magnetic isotherms were analysed with a mean-field model. Values for the magnetic-coupling constant JRCo between the moments of the rare earth (R) and Co in the Hamiltonian H = ΣRCo2JRCoSRSCo were determined and compared with those obtained earlier for RCo4B and R2Co14B compounds.

Magnetic properties of mechanically alloyed Co-Cu

Abstract The changes of the structural and magnetic properties of Co20Cu80 during mechanical alloying were studied as well as the structure and magnetic behaviour of mechanically alloyed Co24Cu76. The magnetic behaviour of the final products was compared to that of similar alloys prepared by different techniques. Clear evidence for superparamagnetism was found in the mechanically alloyed compounds.

Field-induced transitions in RCo12B6 compounds

Abstract The magnetic interaction between the rare earth (R) and the Co moments in ferrimagnetic RCo 12 B 6 (R is heavy rare earth) intermetallic compounds, crystallizing in the hexagonal SrNi 12 B 6 , has been studied by means of high-field magnetisation measurements on fine (single-crystalline) power particles. Magnetisation curves were measured at 4.2 K in the high-field facility at the University of Amsterdam up to 38 T. Field-induced magnetic transitions which reflect changes in the configuration of the R and Co magnetic moments have been observed. The measured magnetisation curves were analysed with a mean-field model. The magnetic coupling constants J RCo between the R and Co moments in the Hamiltonian H =-2 Σ RCo J RCo S R S Co were determined and compared with those derived from the analysis of the compensation temperature and of the magnetic susceptibility measured at the compensation point.

Competing exchange interactions and their relevance for the magnetisation process in RMn6-xCrxSn6 powders (R=Y, Gd, Tb, Dy, Ho, Er)

Abstract The free-powder magnetisation of RMn6-xCrxSn6 compounds has been measured for compounds with R = Y, Gd, Tb, Dy, Ho, Er in fields up to 38 T, and interpreted in terms of simple model, which is also outlined in this paper. From the measurements, estimates for the R-3d mean-field coupling constant (nRT) could be derived for the cases where R = Gd, Tb, Dy, Ho, Er. In turn, the nRT values can be related to the microscopic spin-coupling constant (JRT). In the case of YMn6Sn6 the high-field measurement presents evidence for a very weak antiferromagnetic coupling between the Mn layers. Furthermore, values for the Mn moments (μMn) were also derived from the magnetisation measurements. The estimated μMn values are of the order of 2.0μB.

Magnetic anisotropy of (Sm, Y)2Fe17Ny compounds

A study of the crystal structure and the magnetic properties, especially the magnetocrystalline anisotropy of (Sm1−xYx)2Fe17Ny compounds (x=0, 0.2, 0.4, 0.6, 0.8, and 1.0, 2<y<3) has been performed. All the interstitially nitrided compounds preserve the same Th2Zn17- or Th2Ni17-type structure as the original compounds. The Curie temperatures decrease from 750 to 700 K as x increases from 0 to 1. The anisotropy field decreases linearly with increasing yttrium content. The spin reorientation has been investigated by means of high field magnetization measurements, AC-susceptibility measurements and thermomagnetic analysis, combined with X-ray diffraction. The anisotropy constants K1, K2 and K3 were derived by a phenomenological analysis, using magnetization curves measured in high fields, applied perpendicular to the alignment direction of the powder samples. A tentative spin phase diagram of the series is presented.

Magnetic coupling in rare earth-nickel compounds of the type R2Ni7

Abstract The field dependence (up to 35 T) of the magnetization at 4.2 K of several compounds of the type R Z-x Y x Ni 7 was studied. The magnetic isotherms at 4.2 K were analysed with a mean-field model, from which the magnetic-coupling constant J RNI between the moments of the rare earths and nickel in the Hamiltonian H = θ R J RNi 2 S R · S Ni was estimated. It was found that the coupling constants in the R 2 Ni 7 compounds are almost twice as large as in the R 2 Ni 7 compounds studied previously.