Zero-field magnetic structure and metamagnetic phase transitions of the cobalt chain compound Li$_2$CoCl$_4$

TL;DR

This study investigates the magnetic phases of Li$_2$CoCl$_4$, revealing complex magnetic transitions, the nature of cobalt's spin state, and the magnetic structure through experimental and theoretical methods.

Contribution

It provides the first detailed characterization of the magnetic phases and structure of Li$_2$CoCl$_4$, combining magnetometry, heat capacity, neutron diffraction, and density functional theory.

Findings

Magnetic ordering occurs below 7 K.

Metamagnetic transition near 16.5 kOe.

Ferromagnetic chains with antiferromagnetic interchain interactions.

Abstract

Exploring the uncharacterized magnetic phases of Co$^{2+}$ chain compounds is critical for finding new low-dimensional magnets hosting quantized excitations. We map the unexplored magnetic phases of the Co$^{2+}$ chain compound Li$_2$CoCl$_4$. Magnetometry reveals magnetic ordering below 7 K with a metamagnetic transition near 16.5 kOe and a gradual transition to a field-aligned paramagnetic state above 31 kOe. Curie-Weiss fits to the high temperature susceptibility reveal a high-spin (spin-$\frac{3}{2}$) state for cobalt. Heat capacity data, though, give a magnetic entropy change of 5.46 J/mol, consistent with cobalt effective spin-$\frac{1}{2}$ systems. To characterize the zero-field antiferromagnetic ordering, we separately calculated the energy of proposed magnetic structures with density functional theory and collected 3.5 K neutron diffraction data, finding that Li$_2$CoCl$_4$ has ferromagnetic chains with antiferromagnetic interactions between them. Increasing field rotates these spin chains, producing the antiferromagnetic to intermediate to paramagnetic transition sequence.