Lattice collapse and the magnetic phase diagram of Sr$_{1-x}$Ca$_x$Co$_2$P$_2$

TL;DR

This study explores how chemical substitution in Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ causes a structural transition from uncollapsed to collapsed phases, significantly affecting its magnetic and electronic properties, revealing strong electron count sensitivity.

Contribution

It demonstrates a distinct structural transition at x≈0.5 and links it to changes in magnetic behavior and electron system evolution, highlighting the impact of P-P bonding in this compound family.

Findings

Structural transition occurs near x=0.5

Electronic system shifts from ferromagnetic to antiferromagnetic

Collapse driven by P-P bonding across layers

Abstract

We report that the 122 type Sr$_{1-x}$Ca$_x$Co$_2$P$_2$ solid solution undergoes an anomalous structural transition from the uncollapsed to the collapsed ThCr$_2$Si$_2$ structure at a distinct onset composition near $x=0.5$. Correlated with the structural changes, the electronic system evolves from a nearly ferromagnetic Fermi liquid to an antiferromagnetic metal, through a complex crossover regime. The structural collapse, driven by P-P bonding across the (Sr,Ca) layers, is much more pronounced in this system than it is in the analogous Fe-based system, indicating a strong sensitivity of structure to total electron count in the transition metal pnictide 122 family.