Magnetic phase diagram of Sr$_{1-x}$Ca$_x$Co$_2$P$_2$

TL;DR

This study maps the magnetic phase diagram of Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ using muon spin rotation, revealing various magnetic phases from paramagnetic to antiferromagnetic as calcium content increases.

Contribution

First microscopic muon spin rotation study of Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ revealing detailed magnetic phase transitions with composition.

Findings

Paramagnetic phase persists up to x=0.4.

Spin-glass like phase appears at 0.5 ≤ x ≤ 0.6.

Antiferromagnetic order established at x=1.

Abstract

In order to study the phase diagram from a microscopic viewpoint, we have measured wTF- and ZF-$\mu^+$SR spectra for the Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ 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 $\mu^+$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 $0.5\leq x\leq0.6$, 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 $T_{\rm N}\sim80~$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.