Sign reversal in the exchange bias and the collapse of hysteresis width across the magnetic compensation temperature in a single crystal of Nd0.75Ho0.25Al2

TL;DR

This study investigates the magnetic behavior of Nd0.75Ho0.25Al2, revealing a sign reversal in exchange bias and hysteresis collapse near the compensation temperature, confirming a phenomenological model for ferrimagnetic systems.

Contribution

It provides experimental evidence of exchange bias reversal and hysteresis collapse across the compensation temperature in a single crystal ferrimagnet, supporting theoretical predictions.

Findings

Reversal of exchange bias field (Hexch) across Tcomp.

Collapse of hysteresis width near Tcomp.

Oscillatory magnetoresistance behavior.

Abstract

In the admixed Nd0.75Ho0.25Al2 system, magnetic moments of Nd and Ho occupying the same crystallographic site are antiferromagnetically coupled and the chosen stoichiometry displays a magnetic compensation behavior (Tcomp of about 24 K) in all orientations. In the vicinity of Tcomp, the conduction electron polarization (CEP) assumes the role of a soft ferromagnet exchange coupled to a pseudo-antiferromagnet comprising Nd/Ho moments, resulting in an asymmetry in the hysteretic (M-H) loop, i.e., the notion of an exchange bias field (Hexch). Across Tcomp, the CEP contribution reverses sign, and in consonance, the asymmetry in the M-H loop also undergoes a phase reversal. Interestingly, the width of the M-H loop shows a divergence, followed by a collapse on approaching Tcomp from either end. The observed behavior confirms a long standing prediction based on a phenomenological model for ferrimagnetic systems. The field induced changes across Tcomp leave an imprint of a quasi-phase transition in the heat capacity data. Magneto-resistance (\Delta R / R vs T) has an oscillatory response, in which the changes across Tc and Tcomp can be recognized.