Barkhausen noise in the Random Field Ising Magnet Nd$_2$Fe$_{14}$B

TL;DR

This study investigates Barkhausen noise in Nd$_2$Fe$_{14}$B, a rare-earth ferromagnet, revealing how transverse magnetic fields and temperature influence domain reversal and avalanche dynamics, consistent with theoretical models of disordered systems.

Contribution

It demonstrates how transverse fields tune pinning and avalanche behavior in Nd$_2$Fe$_{14}$B, providing experimental validation of theoretical predictions for Barkhausen avalanches in disordered magnets.

Findings

Avalanche size and energy distributions follow power-law behavior.

Cutoff in distributions depends on transverse field strength.

Two regimes of dynamics identified: disorder-driven and thermally dominated.

Abstract

With sintered needles aligned and a magnetic field applied transverse to its easy axis, the rare-earth ferromagnet Nd$_2$Fe$_{14}$B becomes a room-temperature realization of the Random Field Ising Model. The transverse field tunes the pinning potential of the magnetic domains in a continuous fashion. We study the magnetic domain reversal and avalanche dynamics between liquid helium and room temperatures at a series of transverse fields using a Barkhausen noise technique. The avalanche size and energy distributions follow power-law behavior with a cutoff dependent on the pinning strength dialed in by the transverse field, consistent with theoretical predictions for Barkhausen avalanches in disordered materials. A scaling analysis reveals two regimes of behavior: one at low temperature and high transverse field, where the dynamics are governed by the randomness, and the second at high temperature and low transverse field where thermal fluctuations dominate the dynamics.