Field-induced spin-flop transitions in single-crystalline La$_{0.25}$Pr$_{0.75}$Co$_{2}$P$_{2}$

We report measurements of anisotropic magnetization and magnetoresistance (MR) on single crystals of La$_{0.25}$Pr$_{0.75}$Co$_{2}$P$_{2}$, a novel magnetic alloy with the ThCr$_{2}$Si$_{2}$-type structure, which is a parent structure of the ferro-pnictide high-temperature superconductors. The material exhibits two magnetic transitions in the $c$-axis direction at 240 K and 10.5 K. Below 10K, the magnetization and MR measurements provide corroborating evidence that applying a magnetic field along the $c$-axis induces two successive spin-flop transitions at 0.5 T and 5.5 T. For a magnetic field applied in the \textit{ab }plane, spins cannot be fully polarized at up to 7 T and the MR changes sign from negative to positive at $\sim $20 K with increasing temperature. The observations are consistent with a magnetic configuration, in which the Pr and Co magnetic moments are oriented along the $c$ axis and ordered ferromagnetically within the \textit{ab} plane but antiferomagnetically along the $c$ axis. Details of the microscopic origin of the spin-flop transitions will be discussed.