Emergence of ferromagnetism due to Ir substitutions in single-crystalline Ba[Co(1 x)Ir(x)]2As2

TL;DR

This study investigates how substituting Ir for Co in BaCo2As2 induces short-range ferromagnetism, revealing that Ir doping leads to weak, cluster-based magnetic order without clear thermodynamic phase transition signatures.

Contribution

It demonstrates the emergence of short-range ferromagnetic order due to Ir substitution in BaCo2As2, highlighting the role of spin clusters and itinerant moments in this compound.

Findings

Ferromagnetic signatures appear for x >= 0.11 with TC ≈ 13 K.

Magnetic order is short-range and cluster-based, not long-range.

Heat capacity lacks clear transition features, supporting short-range ordering.

Abstract

The ternary-arsenide compound BaCo2As2 was previously proposed to be in proximity to a quantum-critical point where long-range ferromagnetic (FM) order is suppressed by quantum fluctuations. Here we report the effect of Ir substitution for Co on the magnetic and thermal properties of Ba[Co(1-x)Ir(x)]2As2 (0 <= x <= 0.25) single crystals. These compositions all crystallize in an uncollapsed body-centered-tetragonal ThCr2Si2 structure with space group I4/mmm. Magnetic susceptibility measurements reveal clear signatures of FM ordering for x >= 0.11 with a nearly composition-independent Curie temperature TC = 13 K. The small variation of TC with x, the occurrence of hysteresis in magnetization versus field isotherms at low field and temperature, very small spontaneous and remanent magnetizations < 0.01 muB/f.u., and thermomagnetic irreversibility in the low-temperature region together indicate that the FM response arises from short-range FM ordering of spin clusters as previously inferred to occur in Ca[Co{1-x}Ir{x}]{2-y}As2. Heat-capacity Cp(T) data do not exhibit any clear feature around TC, further indicating that the FM ordering is short-range and/or associated with itinerant moments. The Cp(T) in the paramagnetic temperature regime 25-300 K is well described by the sum of a Sommerfeld electronic contribution and Debye and Einstein lattice contributions where the latter suggests the occurrence of low-frequency optic modes associated with the heavy Ba atoms in the crystals.