Abstract
To investigate the magnetic properties of , we construct an effective spin model, where magnetic moments, crystal-field (CF) parameters, and exchange fields at 0 K are determined by first-principles calculations. Finite-temperature magnetic properties are investigated by using this model. We further develop an analytical method with strong mixing of states with a different quantum number of angular momentum (-mixing), which is caused by a strong exchange field acting on the spin component of electrons. Comparing our analytical results with those calculated by Boltzmann statistics, we clarify that the previous analytical studies for Sm transition-metal compounds overestimate the -mixing effects. The present method enables us to perform a quantitative analysis of the temperature dependence of magnetic anisotropy (MA) with high reliability. The analytical method with model approximations reveals that the -mixing caused by the exchange field increases the spin angular momentum, which enhances the absolute value of the orbital angular momentum and MA constants via spin-orbit interaction. It is also clarified that these -mixing effects remain even above room temperature. Magnetization of shows a peculiar field dependence known as the first-order magnetization process (FOMP), where the magnetization shows an abrupt change at a certain magnetic field. The result of the analysis shows that the origin of FOMP is attributed to competitive MA constants between positive and negative . The sign of appears due to an increase in the CF potential denoted by the parameter () caused by hybridization between -electrons of Fe on the () site and and valence electrons on the Sm site. It is verified that the requirement for the appearance of FOMP is given as .
2 More- Received 2 September 2020
- Accepted 26 October 2020
DOI:https://doi.org/10.1103/PhysRevB.102.184410
©2020 American Physical Society