Complex magnetic phase diagram with multistep spin-flop transitions in La0.25Pr0.75Co2P2

Abstract

$\mathrm{L}{\mathrm{a}}_{0.25}\mathrm{P}{\mathrm{r}}_{0.75}\mathrm{C}{\mathrm{o}}_{2}{\mathrm{P}}_{2}$ crystallizes in the tetragonal $\mathrm{ThC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{i}}_{2}$ structure type and shows multiple magnetic phase transitions driven by changes in temperature and magnetic field. The nature of these transitions was investigated by a combination of magnetic and magnetoresistance measurements and both single crystal and powder neutron diffraction. The Co magnetic moments order ferromagnetically (FM) parallel to the $c$ axis at 282 K, followed by antiferromagnetic (AFM) ordering at 225 K. In the AFM structure, the Co magnetic moments align along the $c$ axis with FM $[\mathrm{C}{\mathrm{o}}_{2}{\mathrm{P}}_{2}]$ layers arranged in an alternating sequence, $\ensuremath{\uparrow}\ensuremath{\uparrow}\ensuremath{\downarrow}\ensuremath{\downarrow}$, which leads to the doubling of the $c$ axis in the magnetic unit cell. Another AFM transition is observed at 27 K, due to the ordering of a half of Pr moments in the $ab$ plane. The other half of Pr moments undergoes AFM ordering along the $c$ axis at 11 K, causing simultaneous reorientation of the previously ordered Pr moments into an AFM structure with the moments being canted with respect to the $c$ axis. This AFM transition causes an abrupt decrease in electrical resistivity at 11 K. Under applied magnetic field, two metamagnetic transitions are observed in the Pr sublattice at 0.8 and 5.4 T. They correlate with two anomalies in magnetoresistance measurements at the same critical fields. A comparison of the temperature- and field-dependent magnetic properties of $\mathrm{L}{\mathrm{a}}_{0.25}\mathrm{P}{\mathrm{r}}_{0.75}\mathrm{C}{\mathrm{o}}_{2}{\mathrm{P}}_{2}$ to the magnetic behavior of $\mathrm{PrC}{\mathrm{o}}_{2}{\mathrm{P}}_{2}$ is provided.