Magnetic phase diagram of Sr_1-xCa_xCo₂P₂

In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-μ⁺SR spectra for the Sr_1-xCa_xCo₂P₂ powder samples with x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1. Due to a characteristic time window and spatial resolution of μ⁺SR, the obtained phase diagram was found to be rather different from that determined by magnetization measurements. That is, as x increases from 0, a Pauli-paramagnetic phase is observed even at the lowest T measured (1.8 K) until x = 0.4, then, a spin-glass like phase appears at 0.5 ≤ x ≤ 0.6, and then, a phase with wide field distribution probably due to incommensurate AF order is detected for x = 0.8, and finally, a commensurate A-type AF ordered phase (for x = 1) is stabilized below T_N ∼ 80 K. Such change is most likely reasonable and connected to the shrink of the c-axis length with x, which naturally enhances the magnetic interaction between the two adjacent Co planes