Disorder and magnetic excitations in CaCrxFe2-xO4 (x=0, 0.5)

Article

关键词: NEUTRON-DIFFRACTION;    MOSSBAUER;   

DOI  :  10.1103/PhysRevB.101.014407

来源: SCIE

【 摘 要 】

Polycrystalline CaFe2O4 and CaCr0.5Fe1.5O4 have been investigated by elastic and inelastic neutron scattering. In agreement with previous reports, CaFe2O4 undergoes two magnetic transitions, first to a B phase, below T-NB = 200 K, then to an A phase, below T-NA = 175 K, while substituted CaCr0.5Fe1.5O4 undergoes a magnetic transition to the B phase only, at T-N = 125 K. Each phase corresponds to staggered antiferromagnetic chains coupled either ferromagnetically (A phase) or antiferromagnetically (B phase). In the A phase of CaFe2O4, inelastic scattering measurements show clearly defined gapped spin waves, which can be modeled with classical calculations, based on a simple exchange Hamiltonian following the topology of the crystal structure. In contrast, in the B phase of both compounds, the interpretation of the excitation spectrum evades completely the classical approach, even at low temperature. These results are interpreted based on an interchain exchange close to the threshold between ferromagnetic and antiferromagnetic bonding geometry. This induces random interchain coupling, thus creating magnetic exchange disorder whose dominating effect is to blur out the magnetic excitation spectrum of the B phase. A magnetoelastic effect, through which the interchain coupling becomes sizably ferromagnetic, and which is not observed in CaCr0.5Fe1.5O4, stabilizes the A phase at low temperature in CaFe2O4.

【 授权许可】

Free