Crystal-field analysis of the magnetic properties measured on aHo2Co15Si2single crystal

Abstract

We have measured the magnetic properties of a ${\mathrm{Ho}}_{2}{\mathrm{Co}}_{15}{\mathrm{Si}}_{2}$ single crystal in the temperature range 5--350 K with magnetic fields applied on the free crystal and along three major crystallographic directions of the fixed crystal. The temperature dependence of the magnetization measured on the free crystal shows that the Ho and Co moments compensate at 35 K, and continuous plane-cone-axis spin-reorientation transitions take place in a certain temperature range above room temperature. The field dependence of the total magnetization shows strong differences when measured along the three main crystallographic directions. In particular, this is the case at low temperatures where the magnetic isotherms are indicative of field-induced magnetic phase transitions. The magnetic isotherms at high temperatures show a marked magnetization anisotropy. We have analyzed our data, especially the field-induced and temperature-induced magnetic phase transitions in terms of a two-sublattice model in which the molecular-field interaction, the crystal-field interaction, and the moment anisotropy are important ingredients. A set of crystalline-electric-field parameters as well as the Ho-Co exchange field has been determined for the ${\mathrm{Ho}}_{2}{\mathrm{Co}}_{15}{\mathrm{Si}}_{2}$ single crystal by fitting the experimental results with model calculations. The calculated magnetic behavior shows a good agreement with the experimental results in the temperature range presently studied, demonstrating the reliability of the determined parameters. It has been found that the Ho moment changes slightly in value during the spin-reorientation transition, and that there is a distinct magnetization anisotropy in the magnetic isotherms at high temperatures. These phenomena are intimately related to the marked direction dependence of the Ho moment.