Torque magnetometry study of the spin reorientation transition and temperature-dependent magnetocrystalline anisotropy in NdCo₅

Abstract

We present the results of torque magnetometry and magnetic susceptibility measurements to study in detail the spin reorientation transition (SRT) and magnetic anisotropy in the permanent magnet NdCo5. We further show simulations of the measurements using first-principles calculations based on density-functional theory and the disordered local moment picture of magnetism at finite temperatures. The good agreement between theory and experimental data leads to a detailed description of the physics underpinning the SRT. In particular we are able to resolve the magnetization of, and to reveal a canting between, the Nd and Co sublattices. The torque measurements carried out in the ac and ab planes near the easy direction allow us to estimate the anisotropy constants, K 1, K 2 and K 4 and their temperature dependences. Torque curves, τ(γ) recorded by varying the direction of a constant magnetic field in the crystallographic ac plane show a reversal in the polarity as the temperature is changed across the SRT (240 < T < 285 K). Within this domain, τ(γ) exhibits unusual features different to those observed above and below the transition. The single crystals of NdCo5 were grown using the optical floating zone technique.

Temperature-dependent magnetocrystalline anisotropy of rare earth/transition metal permanent magnets from first principles: The light RCo5 (R=Y, La-Gd) intermetallics

“…There is also good agreement between calculated and experimental κ values, especially in the SRT region. Indeed, the SRTs are intimately linked to the temperature dependence of κ 1 and κ 2 , with the plane-cone SRT occurring when κ 1 = −2κ 2 and the coneaxis SRT occurring when κ 1 crosses zero [58,59].…”

Spin Orientation and Magnetostriction of Tb1−xDyxFe2 from First Principles

“…We have previously used the Y-analog method to calculate CF coefficients for various RE-transition-metal compounds [25], demonstrating its applicability to describe temperature-and pressure-induced spin-reorientation transitions in the RECo 5 compounds [37,42,43]. Substitution of Tb or Dy with Y to calculate the CF is consistent with the assumptions of the single-ion model [34], namely that the CF depends on the valence electronic structure and not on the RE-4f electrons themselves.…”

Spin orientation and magnetostriction of Tb$_{1-x}$Dy$_{x}$Fe$_{2}$ from first principles

“…In this approach, the potential V (r) which determines the CF coefficients is calculated within DFT for the "Y-analogue" of TbFe 2 or DyFe 2 , which is YFe 2 . Specifically, the components We have previously used the Y-analogue method to calculate CF coefficients for various RE/transition-metal compounds [25], demonstrating its applicability to describe temperature and pressure-induced spin-reorientation transitions in the RECo 5 compounds [37,42,43]. Substituting Tb or Dy with Y to calculate the crystal field is consistent with the assumptions of the single-ion model [34], namely that the CF depends on the valence electronic structure and not on the RE-4f electrons themselves.…”