Magnetocrystalline anisotropic effect in GdCo$_{1-x}$Fe$_x$AsO ($x = 0, 0.05$)

TL;DR

This study maps the complex magnetic phase diagram of GdCo$_{1-x}$Fe$_x$AsO, revealing multiple magnetic transitions, reorientation phenomena, and the effects of Fe doping and magnetic fields on magnetic ordering.

Contribution

It provides the first detailed phase diagram for GdCo$_{1-x}$Fe$_x$AsO, highlighting the interplay of ferromagnetic, antiferromagnetic, and reorientation transitions influenced by Fe doping and magnetic fields.

Findings

Identification of ferromagnetic and antiferromagnetic transitions.

Observation of spin reorientation and magnetic reorientation transitions.

Field effects on magnetic transition temperatures and reorientation fields.

Abstract

From a systematic study of the electrical resistivity $\rho(T,H)$, magnetic susceptibility $\chi(T,H)$, isothermal magnetization $M(H)$ and the specific heat $C(T,H)$, a temperature-magnetic field ($T$-$H$) phase diagram has been established for GdCo$_{1-x}$Fe$_x$AsO ($x = 0$ and $0.05$) polycrystalline compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic (FM) transition of Co $3d$ electrons ($T_\textup{C}^\textup{Co}$) and antiferromagnetic (AFM) transition of Gd $4f$ electrons ($T_\textup{N}^\textup{Gd}$). For the Fe-doped sample ($x=0.05$), an extra magnetic reorientation transition takes place below $T_\textup{N}^\textup{Gd}$, which is likely associated with Co moments. The two magnetic species of Gd and Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM) behavior in the magnetic susceptibility. Upon decreasing the temperature ($T < T_\textup{C}^\textup{Co}$), the magnetocrystalline anisotropy breaks up the FM order of Co by aligning the moments with the local easy axes of the various grains, leading to a spin reorientation transition at $T_\textup{R}^\textup{Co}$. By applying a magnetic field, $T_\textup{R}^\textup{Co}$ monotonically decreases to lower temperatures, while the $T_\textup{N}^\textup{Gd}$ is relatively robust against the external field. On the other hand, the applied magnetic field pulls the magnetization of grains from the local easy direction to the field direction via a first-order reorientation transition, with the transition field ($H_\textup{M}$) increasing upon cooling the temperature.