Size effects in the magnetic behaviour of TbAl_2 milled alloys

TL;DR

This paper investigates how mechanical milling affects the magnetic properties of TbAl_2 alloys, revealing size-induced disorder and cluster-glass behavior at nanometer scales, with implications for magnetic domain dynamics.

Contribution

It provides new insights into the size-dependent magnetic behavior of TbAl_2, highlighting the transition from domain wall processes to cluster-glass phenomena due to milling-induced disorder.

Findings

Grain size decreases to 14 nm after 300 hours of milling.

Disordered spin arrangements dominate below 45 K, indicating glassy behavior.

Coercivity varies with grain size, showing a transition between multi- and single-domain states.

Abstract

The study of the magnetic properties depending upon mechanical milling of the ferromagnetic polycrystalline TbAl_2 material is reported. The Rietveld analysis of the X-ray diffraction data reveals a decrease of the grain size down to 14 nm and -0.15 % of variation of the lattice parameter, after 300 hours of milling time. Irreversibility in the zero field cooled - field cooled (ZFC-FC) DC-susceptibility and clear peaks in the AC susceptibility between 5 and 300 K show that the long-range ferromagnetic structure is inhibited in favour of a disordered spin arrangement below 45 K. This glassy behaviour is also deduced from the variation of the irreversibility transition with the field (H^{2/3}) and frequency. The magnetization process of the bulk TbAl_2 is governed by domain wall thermal activation processes. By contrast, in the milled samples, cluster-glass properties arise as a result of cooperative interactions due to the substitutional disorder. The interactions are also influenced by the nanograin structure of the milled alloys, showing a variation of coercivity with the grain size, below the crossover between the multi- and single-domain behaviours.