New insights into the magnetism of DyCo$_{5}$

TL;DR

DyCo5 exhibits complex ferrimagnetism from competing Dy 4$f$ and Co 3$d$ sublattices, leading to a compensation point at $T_{ ext{comp}}$ and a spin-reorientation region near $T_{ ext{SR}}$. The study combines high-field magnetization measurements up to $14$ T and temperatures up to $600$ K with a multiscale theoretical framework—DFT+DMFT+ASD and an effective spin model with crystal-field inputs—to capture anisotropy evolution, sublattice non-collinearity, and high-field behavior. Key findings include a large magnetization anisotropy, a residual magnetization at compensation under finite fields, and a quantitative reproduction of saturation trends and $M(T)$ curves across temperatures, revealing the distinct temperature dependencies of the Dy and Co sublattices. The work underscores the necessity of integrating crystal-field effects, finite-temperature dynamics, and intersublattice exchange to understand and predict the magnetic properties of DyCo5 with potential implications for high-temperature magnetism and spintronic applications.

Abstract

In this work, we present the first magnetization measurements of DyCo$_5$ single crystals in magnetic fields up to 14 T, spanning a temperature range up to 600 K. Our investigation reveals several unique features, including a significant magnetization anisotropy and an observed minimum in spontaneous magnetization near the compensation point, phenomena not previously reported. This work also uncovers the complex magnetic behavior of DyCo$_5$, with a pronounced interplay between the Dy and Co sublattices, each exhibiting distinct temperature-dependent magnetic properties. The combination of dynamical mean-field theory (DMFT), atomistic spin-dynamics (ASD) simulations, and the Effective Spin Model (ESM) for rare-earth compounds successfully explains the experimental data across both low and high temperatures. Our theoretical approach not only explains the observed magnetic anisotropy and the behavior near the compensation temperature but also successfully reproduces key experimental features such as the saturation behavior at high fields and the evolution of the magnetic moment at different temperatures.

Figures (13)

• Figure 1: (Color online) (a-h) Magnetisation curves of DyCo$_{5}$ single crystal measured along the three principal crystallographic directions in magnetic fields up to 14 T and within a temperature range of 10-600K. Magnetisation curves of a loose sample are also shown in (c-h). (i) Spontaneous magnetization measured along the a and c directions (extrapolated to the demagnetisation field)
• Figure 2: Magnetization curves of DyCo$_{5}$ at 100 K, 150 K, 200 K, and 300 K calculated within the framework of the effective spin model and compared with the experimental data. The green and red lines indicate results along the principal [100] and [001] crystallographic directions, respectively.
• Figure 3: (Color online) Exchange interactions $J_{ij}$ in DyCo$_{5}$ calculated with RSPt. The inset shows $J_{ij}$ for Dy-Co and Dy-Dy interactions.
• Figure 4: (Color online) Absolute values of $K_{1}$ for Co and Dy as a function of temperature calculated in this work in the ESM. Magnetocrystalline anisotropy calculated within the single-ion approximation by Radwanski in RADWANSKI1986120 as well as by Greedan and Rao GREEDAN1973387 are shown as well. Note, that Dy shows in-plane (negative values) anisotropy, unlike Co.
• Figure 5: (Color online) (a) Temperature dependence of the magnetic moments of Co and Dy, as well as the total moment, obtained by using the effective spin model. (b) Temperature dependence of the magnetic moment per unit cell obtained with ASD simulation for three different calculated $K_{1}(T)$. The vertical dotted lines show the experimental interval between T$_{\bf SR1}$ and T$_{\bf SR2}$. (c) Temperature dependence of the magnetic moment per unit cell around T$_{\bf comp}$ with and without magnetic anisotropy ($K_{1}(T)$ calculated in the current work). For the former case, M(T) is also shown with and without the external field of 2 T. Note that there is residual magnetization around the compensation point. The Hamiltonian used in ASD simulations is shown as Eq. \ref{['eq:HASD']}.