Tunable Cobalt Vacancies and Related Properties in LaCoxAs2

TL;DR

This study investigates how tunable cobalt vacancies in LaCoxAs2 influence its structural, magnetic, and electronic properties, revealing a method to control magnetism in ThCr2Si2-type compounds.

Contribution

It provides detailed analysis of cobalt vacancy formation, their effects on properties, and demonstrates tuning of magnetic and electrical behavior through vacancy control.

Findings

Co occupancy can be tuned between 1.98 and 1.61.

Co vacancies significantly alter magnetic and electrical properties.

First principles calculations confirm vacancy effects on spin polarization and density of states.

Abstract

The origin of transition metal vacancies and their effects on the properties of ThCr2Si2-type compounds have been less studied and poorly understood. Here we carefully investigate the structure, physical properties, and electronic structure for a series of lanthanum cobalt arsenides with nominal composition of LaCoxAs2 (1.6 < = x < = 2.1). It is revealed that the occupancy of Co can be tuned between 1.98(1) and 1.61(1). The structural analyses based on X-ray and neutron diffractions show the existence of Co vacancies results from charge balance due to the formation of bond between As-As. These Co vacancies affect the magnetic and electrical properties greatly, adjusting the Curie temperature from 205 to 47 K and increasing the resistivity by more than 100%. First principles calculations indicate that the Co vacancies weaken the spin polarization and reduce the density of states at the Fermi level, resulting in decreased Curie temperature and increased resistivity, respectively. Our results address the importance of transition metal vacancies in ThCr2Si2-type materials and offer a reliable route to tune the magnetism of ThCr2Si2-type structure.