Signature effects of spin clustering and distribution of spin couplings on magnetization behaviour in Ni-Fe-Mo and Ni-Fe-W alloys

TL;DR

This study investigates how spin clustering and distribution of spin couplings influence magnetization in Ni-Fe-Mo and Ni-Fe-W alloys, revealing unique low-temperature and critical behavior linked to spin dynamics and clustering effects.

Contribution

It introduces a detailed analysis of spin clustering effects on magnetization in disordered alloys, supported by experimental data and theoretical calculations, highlighting distinctive temperature-dependent behaviors.

Findings

Enhanced spin-wave parameter B with Fe dilution

Decreased critical amplitudes with Fe dilution

Identification of two energy scales in spin dynamics

Abstract

The spontaneous magnetization as a function of temperature is investigated for a number of disordered Ni-Fe-Mo and Ni-Fe-W alloys using superconducting quantum interference device magnetometry, with a focus on the low-T behavior as well as the critical exponents associated with the magnetic phase transition. While the low-T magnetization is found to be well described by Bloch's T^{3/2} law, an extraordinary enhancement of the spin-wave parameter B and the reduced coefficient B_{3/2}=BT_C ^{3/2} are observed with increasing Fe dilution as compared to conventional 3d ferromagnets, whereas the critical amplitudes are found to decrease systematically. Recent locally self-consistent calculations of finite-temperature spin dynamics in a generic diluted magnet provide an understanding in terms of two distinct energy scales associated with weakly coupled bulk spins in the FM matrix and strongly coupled cluster spins. In view of similar behaviour observed in diluted magnetic semiconductors and other ferromagnetic alloys, it is proposed that these distinctive features corresponding to the three important temperature regimes provide macroscopic indicators of signature effects of spin clustering on magnetization behaviour in disordered ferromagnets.