title: Size effects in the magnetic behaviour of TbAl(2) milled alloys.
abstract: The study of the magnetic properties depending upon mechanical milling of the ferromagnetic polycrystalline TbAl(2) material is reported. Rietveld analysis of the x-ray diffraction data reveals a decrease in the grain size down to 14 nm and a -0.15% variation in the lattice parameter, after 300 h 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. In 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 in coercivity with the grain size, below the crossover between the multi- and single-domain behaviours.
authors.affiliation: Departamento CITIMAC, Universidad de Cantabria, Santander 39005, Spain.
authors.forename: D P
authors.initials: DP
authors.lastname: Rojas
authors.forename: L
authors.initials: L
authors.lastname: Fernández Barquín
authors.forename: J
authors.initials: J
authors.lastname: Rodríguez Fernández
authors.forename: J I
authors.initials: JI
authors.lastname: Espeso
authors.forename: J C
authors.initials: JC
authors.lastname: Gómez Sal