Abstract
compounds crystallizing in the tetragonal -type structure (space group ) and undergoing a structural phase transition to an orthorhombic structure () at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of is described by an incommensurate propagation vector with and . The magnetic moments order antiferromagnetically within the planes stacked along the axis and are arranged along the direction close to the orthorhombic axis with a maximum value of 1.5(1) . reveals a magnetic structure composed of two components: the first is described by the propagation vector , and the second one propagates with . 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 and describe also the magnetic structure of substituted compounds, except the one with with magnetic structure described by and stays on the border between pure 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 , while only two crystal field (CF) excitations are expected from the splitting of ground state of the 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 . 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 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the series is discussed and crystal field parameters determined.
6 More- Received 26 February 2016
- Revised 10 January 2017
DOI:https://doi.org/10.1103/PhysRevB.95.085107
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