Tunable Cobalt Vacancies and Related Properties inLaCoxAs2.

Theorigin of transition metal vacancies and their effects on theproperties of ThCr2Si2-type compounds have beenless studied and poorly understood. Here we carefully investigatethe structure, physical properties, and electronic structure for aseries of lanthanum cobalt arsenides with nominal composition of LaCoxAs2(1.6 ≤ x≤ 2.1). It is revealed that the occupancy of Co can be tunedbetween 1.98(1) and 1.61(1). The structural analyses based on X-rayand neutron diffractions show the existence of Co vacancies resultsfrom 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 theresistivity by more than 100%. First-principles calculations indicatethat the Co vacancies weaken the spin polarization and reduce thedensity of states at the Fermi level, resulting in decreased Curietemperature and increased resistivity, respectively. Our results addressthe importance of transition metal vacancies in ThCr2Si2-type materials and offer a reliable route to tune the magnetismof ThCr2Si2-type structure. [ABSTRACT FROM AUTHOR]