Unconventional ferromagnetic and spin-glass states of the reentrant spin glass Fe0.7Al0.3

TL;DR

This study investigates the spin excitations in Fe0.7Al0.3, revealing a transition from propagating spin waves to diffusive modes and persistent short-range correlations, highlighting complex magnetic states.

Contribution

It provides the first detailed inelastic neutron scattering analysis of Fe0.7Al0.3, identifying unconventional ferromagnetic and spin-glass states with a quantitative model for spin dynamics.

Findings

Spin wave modes become diffusive beyond a critical wave vector.

Spin dynamics in the spin glass phase shows strong q-dependence.

A quantitative model for spin excitations in the ferromagnetic phase is developed.

Abstract

Spin excitations of single crystal Fe0.7Al0.3 were investigated over a wide range in energy and reciprocal space with inelastic neutron scattering. In the ferromagnetic phase, propagating spin wave modes become paramagnon-like diffusive modes beyond a critical wave vector q0, indicating substantial disorder in the long-range ordered state. In the spin glass phase, spin dynamics is strongly q-dependent, suggesting remnant short-range spin correlations. Quantitative model for S(energy,q) in the ``ferromagnetic'' phase is determined.