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Magnetic phase diagram of magnetocaloric TmFeO$_3$

K. I. Tkachenko, P. Fabrykiewicz, A. K. Ovsianikov, M. Meven, O. V. Usmanov, I. A. Zobkalo, K. A. Shaykhutdinov, K. Yu. Terentjev, S. V. Semenov, E. Ressouche, K. Beauvois

TL;DR

This study maps the magnetic phase diagram of the rare-earth orthoferrite $TmFeO_3$ under external magnetic fields applied along the crystallographic $b$- and $c$-axes using neutron diffraction on high-quality single crystals. By refining magnetic structures from field- and temperature-dependent Bragg intensities, the work shows that $T_N$ is set by Fe–Fe interactions, that the spin-reorientation transition proceeds through a mixed $Γ24$ phase and ultimately to $Γ2$, and that the field direction differentially shifts $T_{SR}$—increasing it for $H ightarrow c$ and decreasing it for $H ightarrow b$—while revealing field-induced phases and a low-temperature regime where Fe and Tm sublattices partially decouple. The results highlight the interplay of 3d–4f exchange and anisotropy in driving SR and account for the observed magnetocaloric response around $T oughly 10$–$20$ K. These findings advance understanding of SR dynamics in orthoferrites and inform control of magnetocaloric and spintronic functionalities.

Abstract

Neutron diffraction experiments of TmFeO$_3$ single crystals were performed in the external magnetic fields. The field along $c$-axis increases temperature of spin-reorientation transition $T_{SR}$ from phase $Γ4$ to $Γ2$. Application of the field along $b$-axis led to the decrease of $T_{SR}$ and to the formation of new phases. Based on the temperature and field dependence of the Bragg reflection intensity, the configuration of magnetically induced phases was proposed.

Magnetic phase diagram of magnetocaloric TmFeO$_3$

TL;DR

This study maps the magnetic phase diagram of the rare-earth orthoferrite under external magnetic fields applied along the crystallographic - and -axes using neutron diffraction on high-quality single crystals. By refining magnetic structures from field- and temperature-dependent Bragg intensities, the work shows that is set by Fe–Fe interactions, that the spin-reorientation transition proceeds through a mixed phase and ultimately to , and that the field direction differentially shifts —increasing it for and decreasing it for —while revealing field-induced phases and a low-temperature regime where Fe and Tm sublattices partially decouple. The results highlight the interplay of 3d–4f exchange and anisotropy in driving SR and account for the observed magnetocaloric response around – K. These findings advance understanding of SR dynamics in orthoferrites and inform control of magnetocaloric and spintronic functionalities.

Abstract

Neutron diffraction experiments of TmFeO single crystals were performed in the external magnetic fields. The field along -axis increases temperature of spin-reorientation transition from phase to . Application of the field along -axis led to the decrease of and to the formation of new phases. Based on the temperature and field dependence of the Bragg reflection intensity, the configuration of magnetically induced phases was proposed.

Paper Structure

This paper contains 6 sections, 2 equations, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Experimental part
  3. Result and discussion
  4. Structure study
  5. Magnetic scattering dependence on magnetic field
  6. Conclusions

Figures (4)

  • Figure 1: (a) Crystal structure of $\rm{TmFeO_3}$ at $T=300$ K; (b) Magnetic structure of $\rm{TmFeO_3}$ at $T=20$ K. Blue arrows -- Fe magnetic moments, red arrows -- Tm magnetic moments, the magnitude of the arrow for Tm is increased five times for the sake of visualization; c) Antiferroelectric order of $\rm{TmFeO_3}$, green arrows -- electric dipole moment.
  • Figure 2: Temperature dependencies of reflections intensities ($-110$), ($-220$) for external magnetic field directed a) b) along the b-axis and c) d) along the c-axis.
  • Figure 3: Schematic of the magnetic phase diagram for $\rm{TmFeO_3}$ a) external magnetic field along the b-axis b) along c-axis. Squares, circles and triangles are the inflection points of the temperature dependence function of the intensity for different reflections. Roman numbers designate regions corresponding by different magnetic representation: I -- $\Gamma 4$; II -- $\Gamma 24$; III -- $\Gamma 2$; IV -- $\Gamma^{\rm{Fe}}_4 + \Gamma^{\rm{Tm}}_2$; V -- $\Gamma^{\rm{Fe}}_4 - \Gamma^{\rm{Tm}}_4$. Magnetic configurations, corresponding each region, are shown schematically without magnetic moments scaling.
  • Figure 4: Hysteresis of G-type peak ($-3,1,0$) intensity in magnetic fields along the b-axis at 20 K. Error bars are of the size of the symbols.