Switchable Hardening of a Ferromagnet at Fixed Temperature

TL;DR

This paper demonstrates how an external transverse magnetic field can dynamically control the domain structure and magnetic hardness of a disordered ferromagnet at fixed temperature, revealing quantum tunneling effects and phase transitions.

Contribution

It introduces a novel isothermal method to switch the hardness of a ferromagnet using transverse magnetic fields, highlighting quantum effects in domain wall dynamics.

Findings

Transverse fields increase domain pinning near the transition temperature.

Quantum tunneling dominates domain dynamics at low temperatures.

Principles are applicable to room-temperature ferromagnets.

Abstract

The intended use of a magnetic material, from information storage to power conversion, depends crucially on its domain structure, traditionally crafted during materials synthesis. By contrast, we show that an external magnetic field applied transverse to the preferred magnetization of a model disordered uniaxial ferromagnet is an isothermal regulator of domain pinning. At elevated temperatures, near the transition into the paramagnet, modest transverse fields increase the pinning, stabilize the domain structure, and harden the magnet, until a point where the field induces quantum tunneling of the domain walls and softens the magnet. At low temperatures, tunneling completely dominates the domain dynamics and provides an interpretation of the quantum phase transition in highly disordered magnets as a localization/delocalization transition for domain walls. While the energy scales of the rare earth ferromagnet studied here restrict the effects to cryogenic temperatures, the principles discovered are general and should be applicable to existing classes of highly anisotropic ferromagnets with ordering at room temperature or above.