The magnetic, thermodynamic, and pyroelectric properties of LiFeP${}_2$O${}_7$ single crystals are investigated with emphasis on the magnetoelectric interaction of the electrical polarization with the magnetic order parameter. The magnetic order below $T_N\simeq 27$ K is found to be a canted antiferromagnet with a weak ferromagnetic component along the $b$ axis. A sharp peak of the pyroelectric current at $T_N$ proves the strong internal magnetoelectric interaction resulting in a sizable polarization decrease at the onset of magnetic order. The magnetoelectric effect in external magnetic fields combines a linear and a quadratic field dependence below $T_N$. Thermal expansion data show a large uniaxial magnetoelastic response and prove the existence of strong spin-lattice coupling. LiFeP${}_2$O${}_7$ is a polar compound with a strong interaction of the magnetic order parameter with the electric polarization and the lattice.

• Received 6 June 2012

DOI:https://doi.org/10.1103/PhysRevB.86.094414