Time-of-flight elastic and inelastic neutron scattering studies on the localized $4d$ electron layered perovskite La${}_5$Mo${}_4$O${}_{16}$

Abstract

The magnetic structure and spin-wave excitations in the quasi-square-lattice layered perovskite compound La${}_5$Mo${}_4$O${}_{16}$ were studied by a combination of neutron diffraction and inelastic neutron scattering techniques using polycrystalline sample. Neutron powder diffraction refinement revealed that the magnetic structure is ferrimagnetic in the $ab$ plane with antiferromagnetic stacking along the $c$ axis where the magnetic propagation vector is $\mathbf{k}=\left(0,0,\frac{1}{2}\right)$. The ordered magnetic moments are estimated to be $0.54(2){\mu }_{\text{B}}$ for Mo${}^{5+}$ ($4d^1$) ions and $1.07(3){\mu }_{\text{B}}$ for Mo${}^{4+}$ ($4d^2$) ions at 4 K, which are about half of the expected values. The inelastic neutron scattering results display strong easy-axis magnetic anisotropy along the $c$ axis due to the spin-orbit interaction in Mo ions evidenced by the spin gap at the magnetic zone center. The model Hamiltonian consisting of in-plane anisotropic exchange interactions, the interlayer exchange interaction, and easy-axis single-ion anisotropy can explain our inelastic neutron scattering data well. Strong Ising-like anisotropy and weak interlayer coupling compared with the intralayer exchange interaction can explain both the high-temperature magnetoresistance and long-time magnetization decay recently observed in La${}_5$Mo${}_4$O${}_{16}$.

arXiv comment6 pages, 4 figures

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