Co-existence of short- and long-range magnetic order in LaCo$_2$P$_2$

TL;DR

This study uses muon spin techniques and first principles calculations to reveal that LaCo$_2$P$_2$ exhibits co-existing short-range and long-range magnetic order near its Curie temperature, highlighting complex magnetic interactions.

Contribution

It provides the first detailed experimental and theoretical evidence of co-existing magnetic orders in LaCo$_2$P$_2$, emphasizing the competition between 2D and 3D magnetic interactions.

Findings

Long-range ferromagnetic order at T_C=130.91 K

Short-range magnetic order exists between 124 K and T_C

Co-existence of SRO and LRO is intrinsic due to interaction competition

Abstract

The ferromagnetic (FM) nature of the metallic LaCo$_2$P$_2$ was investigated with the positive muon spin rotation, relaxation and resonance ($\mu^+$SR) technique. Transverse and zero field $\mu^+$SR measurements revealed that the compound enters a long range FM ground state at $T_{\rm C}=130.91(65)$~K, consistent with previous studies. Based on the reported FM structure, the internal magnetic field was computed at the muon sites, which were predicted with first principles calculations. The computed result agree well with the experimental data. Moreover, although LaCo$_2$P$_2$ is a paramagnet at higher temperatures $T>160$~K, it enters a short range ordered (SRO) magnetic phase for $T_{\rm C}<T\leq160$~K. Measurements below the vicinity of $T_{\rm C}$ revealed that the SRO phase co-exists with the long range FM order at temperatures $124\leq T\leq T_{\rm C}$. Such co-existence is an intrinsic property and stems from competition between the 2D and 3D interactions/fluctuations.