Coupling of magnetism, crystal lattice, and transport in EuCuP and EuCuAs

EuCuP and EuCuAs are members of a family of materials with candidates for realizing magnetically tuned electronic topology. In this work, the magnetic phase transitions and magnetoelastic coupling of EuCuP and EuCuAs have been investigated. Around the Curie temperature, the thermal expansion coefficient and specificheat capacity of EuCuP are found to have two closely spaced features, at approximately 30 and 31.3 K, which may indicate a cascading magnetic transition or perhaps an electronic transition closely coupled to the magnetic ordering. The zero-field magnetoelastic coupling appears to be stronger in EuCuP than in EuCuAs, and field-dependent measurements suggest this is due to the dominant ferromagnetic interaction in EuCuP as opposed to antiferromagnetic order in EuCuAs below T-N = 13.5 K. Thermal expansion is anisotropic around T-N in EuCuAs, with a maximum expansion along [001] occurring above T-N prior to a stiffening of this c-axis component on cooling through T-N; the expansion of the basal plane has a lambda-like peak centered slightly above T-N. Matching these behaviors, the ac susceptibility data for EuCuAs suggest the presence of strong ferromagnetic correlations above T-N in the vicinity where the c-axis expansion peaks. Both compounds possess similar electrical and thermoelectric transport behaviors, with short-range magnetic order likely playing an important role above T-C or T-N. Transport properties suggest these are predominantly hole doped due to intrinsic defects, and narrow-gap semiconducting or semimetallic behavior may be achievable if the underlying defects can be tuned.

Automated summary

EuCuP and EuCuAs were studied to investigate their magnetic phase transitions and magnetoelastic coupling. EuCuP exhibited two closely spaced features in thermal expansion and specific heat capacity around the Curie temperature, possibly indicating a cascading magnetic transition or an electronic transition closely coupled to the magnetic ordering. Stronger zero-field magnetoelastic coupling was observed in EuCuP compared to EuCuAs, which was attributed to the dominant ferromagnetic interaction in EuCuP and antiferromagnetic order in EuCuAs. Anisotropic thermal expansion and strong ferromagnetic correlations were observed in EuCuAs above T-N. Both compounds showed similar electrical and thermoelectric transport behaviors, suggesting intrinsic defects and potential for achieving narrow-gap semiconducting or semimetallic behavior with defect tuning.