Nanocrystalline Nd(2)Fe(17) powders have been obtained by means of high-energy ball milling from nearly single-phase bulk alloys produced by arc melting and high temperature homogenization annealing. The rhombohedral Th(2)Zn(17)-type crystal structure of the bulk alloy remains unaltered after the milling process, with almost unchanged values for the cell parameters. However, the severe mechanical processing induces drastic microstructural changes. A decrease of the mean crystalline size down to around 10 nm is observed, giving rise to a considerable augmentation of the disordered inter-grain boundaries. This modification of the microstructure affects the magnetic behaviour of the milled powders, although the magnetic structure remains collinear ferromagnetic. While a unique ferro-to-paramagnetic transition temperature, T(C) = 339 ± 2 K, is observed in the bulk alloy, the nanocrystalline samples exhibit a more likely distribution of T(C) values. The latter seems to be responsible for the significant broadening of the temperature range in which magneto-caloric effect is observed, and the lowering of the maximum value of the magnetic entropy change.

CePd 2 Al 2−x Ga x compounds crystallizing in the tetragonal CaBe 2 Ge 2 -type structure (space group P 4/nmm) and undergoing a structural phase transition to an orthorhombic structure (Cmme) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd 2 Al 2 is described by an incommensurate propagation vector k = (δ x , 1 2 + δ y ,0) with δ x = 0.06 and δ y = 0.04. The magnetic moments order antiferromagnetically within the ab planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) μ B /Ce 3+ . CePd 2 Ga 2 reveals a magnetic structure composed of two components: the first is described by the propagation vector, 0), and the second one propagates with k 2 = (0, 1 2 ,0). The magnetic moments of both components are aligned along the same direction-the orthorhombic [100] direction-and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors k 1 and k 2 describe also the magnetic structure of substituted CePd 2 Al 2−x Ga x compounds, except the one with x = 0.1. CePd 2 Al 1.9 Ga 0.1 with magnetic structure described by k and k 1 stays on the border between pure CePd 2 Al 2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd 2 Al 2 , while only two crystal field (CF) excitations are expected from the splitting of ground state J = 5 2 of the Ce 3+ ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd 2 Al 2 . A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd 2 Ga 2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd 2 Al 2−x Ga x series is discussed and crystal field parameters determined.