Magnetic compensation phenomenon and the sign reversal in the exchange bias field in a single crystal of Nd _0.75 Ho _0.25 Al ₂

Abstract

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