Suppression of antiferromagnetic order and strong ferromagnetic spin fluctuations in Ni-doped CaCo2As2 single crystals

TL;DR

This study investigates how Ni doping suppresses antiferromagnetic order and induces strong ferromagnetic spin fluctuations in CaCo2As2, revealing significant changes in magnetic properties and electronic structure.

Contribution

It provides new insights into the effects of Ni substitution on magnetic frustration and spin fluctuations in CaCo2As2, supported by experimental and DFT calculations.

Findings

Antiferromagnetic transition temperature decreases with Ni doping.

Strong ferromagnetic fluctuations develop for 0.11 < x < 0.52.

FM fluctuations are confirmed by heat capacity and DFT calculations.

Abstract

CaCo2As2 is a unique itinerant system having strong magnetic frustration. Here we report the effect of electron doping on the physical properties resulting from Ni substitutions for Co. The A-type antiferromagnetic transition temperature TN = 52 K for x = 0 decreases to 22 K with only 3 percent Ni substitution and is completely suppressed for x > 0.11. For 0.11 < x < 0.52 strong ferromagnetic (FM) fluctuations develop as revealed by magnetic susceptibility chi(T) measurements. Heat-capacity Cp(T) measurements reveal the presence of FM quantum spin fluctuations for 0.11 < x < 0.52. Our density-functional theory (DFT) calculations confirm that FM fluctuations are enhanced by Ni substitutions for Co. The Sommerfeld electronic heat-capacity coefficient is enhanced for x = 0, 0.21, and 0.42 by about a factor of two compared to DFT calculations of the bare density of states at the Fermi energy. The crystals with x > 0.52 do not exhibit FM spin fluctuations or magnetic order, which was found from the DFT calculations to arise from a Stoner transition. Neutron-diffraction studies of crystals with x = 0.11 and 0.16 found no evidence of A-type ordering as observed in CaCo2As2 or of other common magnetic structures.