Synthesis and Characterization
of the Crystal Structure
and Magnetic Properties of the New Fluorophosphate LiNaCo[PO<sub>4</sub>]F
- Publication date
- Publisher
Abstract
The new compound LiNaCo[PO<sub>4</sub>]F was synthesized
by a solid
state reaction route, and its crystal structure was determined by
single-crystal X-ray diffraction measurements. The magnetic properties
of LiNaCo[PO<sub>4</sub>]F were characterized by magnetic susceptibility,
specific heat, and neutron powder diffraction measurements and also
by density functional calculations. LiNaCo[PO<sub>4</sub>]F crystallizes
with orthorhombic symmetry, space group <i>Pnma</i>, with <i>a</i> = 10.9334(6), <i>b</i> = 6.2934(11), <i>c</i> = 11.3556(10) Å, and <i>Z</i> = 8. The
structure consists of edge-sharing CoO<sub>4</sub>F<sub>2</sub> octahedra
forming CoFO<sub>3</sub> chains running along the <i>b</i> axis. These chains are interlinked by PO<sub>4</sub> tetrahedra
forming a three-dimensional framework with the tunnels and the cavities
filled by the well-ordered sodium and lithium atoms, respectively.
The magnetic susceptibility follows the Curie–Weiss behavior
above 60 K with θ = −21 K. The specific heat and magnetization
measurements show that LiNaCo[PO<sub>4</sub>]F undergoes a three-dimensional
magnetic ordering at <i>T</i><sub><i>mag</i></sub> = 10.2(5) K. The neutron powder diffraction measurements at 3 K
show that the spins in each CoFO<sub>3</sub> chain along the <i>b</i>-direction are ferromagnetically coupled, while these FM
chains are antiferromagnetically coupled along the <i>a</i>-direction but have a noncollinear arrangement along the <i>c</i>-direction. The noncollinear spin arrangement implies the
presence of spin conflict along the <i>c</i>-direction.
The observed magnetic structures are well explained by the spin exchange
constants determined from density functional calculations
