Slow magnetic dynamics and hysteresis loops of a bulk ferromagnet

TL;DR

This study investigates the magnetic dynamics and hysteresis behavior of a new bulk ferromagnet, Co7(TeO3)4Br6, revealing detailed relaxation processes and modeling spin reversal with thermal activation, providing insights into magnetic hysteresis mechanisms.

Contribution

It introduces a comprehensive experimental and theoretical analysis of magnetic relaxation and hysteresis in a novel ferromagnetic compound, with a focus on dynamic coercivity and frequency-dependent relaxation rates.

Findings

Large activation energy of 17.2 meV indicating slow magnetic dynamics

Quantitative agreement between experimental hysteresis data and the thermal-activation model

Detection of low-frequency limitations due to domain wall pinning effects

Abstract

Magnetic dynamics of a bulk ferromagnet, a new single crystalline compound Co7(TeO3)4Br6, was studied by ac susceptibility and the related techniques. Very large Arrhenius activation energy of 17.2 meV (201 K) and long attempt time (2x10^(-4)s) span the full spectrum of magnetic dynamics inside a convenient frequency window, offering a rare opportunity for general studies of magnetic dynamics. Within the experimental window the ac susceptibility data build almost ideally semicircular Cole-Cole plots. Comprehensive study of experimental dynamic hysteresis loops of the compound is presented and interpreted within a simple thermal-activation-assisted spin lattice relaxation model for spin reversal. Quantitative agreement between the experimental results and the model's prediction for dynamic coercive field is achieved by assuming the central physical quantity, the Debye relaxation rate, to depend on frequency, as well as on the applied field strength and sample temperature. Cross-over between minor- to major hysteresis loops is carefully analyzed. Low-frequency limitations of the model, relying on domain wall pinning effects, are experimentally detected and appropriately discussed.