Magnetic Structure and Susceptibility of CoSe$_2$O$_5$: A Low Dimensional Antiferromagnet

TL;DR

This study reveals the magnetic structure of CoSe$_2$O$_5$, showing a low-temperature antiferromagnetic order with canted spins and a gapped heat capacity, using magnetization, specific heat, and neutron diffraction techniques.

Contribution

The paper provides the first detailed investigation of the magnetic ordering and structure of CoSe$_2$O$_5$ using neutron diffraction and thermodynamic measurements.

Findings

Long-range antiferromagnetic order below 8.5 K

Magnetic moments are canted by ±8° from the a axis

Presence of a 6.5 K energy gap in heat capacity

Abstract

CoSe$_2$O$_5$ has a crystal structure consisting of zig-zag chains of edge shared CoO$_6$ octahedra running along the c axis, with the chains separated by Se$_2$O$_5^{2-}$ units. Magnetic susceptibility measurements indicate a transition at 8.5 K to an ordered state. We investigate here the nature of this magnetic ordering using magnetization and specific heat measurements in addition to powder neuttron diffraction. A transition to long-range antiferromagnetic order is found below $T_N$ = 8.5 K as identified by magnetic susceptibility measurements and magnetic Bragg reflections, with a propagation vector $\mathbf{k}$ = 0. The magnetic structure shows that the moments align perpendicular to the c-axis, but with the spins canting with respect to the a axis by, alternately, $+8^\circ$ and $-8^\circ$. Interestingly, the low-field magnetic susceptibility does not show the anticipated cusp-like behavior expected for a well-ordered antiferromagnet. When the susceptibility is acquired under field-cooling conditions under a 10 kOe field, the the usual downturn expected for antiferromagnetic ordering is obtained. Heat capacity measurements at low temperatures indicate the presence of gapped behavior with a gap of 6.5 K.