Electronic structure, magnetic order and anisotropic magnetoresistance in $\mathbf{Eu_{1-x}Gd_xCd_2P_2}$ (0 $\le$ x $\le$1)

Overview & Synopsis

Recently, $\text{EuCd}_2\text{P}_2$ has attracted increased attention for its colossal magnetoresistive (CMR) property, the mechanism of which seems to deviate from that of known canonical CMR compounds such as manganites. Many studies underscore the role of low density of hole carriers caused by Eu vacancies, particularly in stabilizing ferromagnetic (FM) order and modifying electrical transport and magnetoresistive responses in this compound. A magnetic polaron based mechanism rather than double exchange based mechanism is being proposed to explain the CMR effect for this compound. In this work, we explore the effect of elctron doping on the magnetic transition and CMR behaviour via Gd substitution at Eu sites with varying concentration (x) in Eu$_{1-x}$Gd$_{x}$Cd$_2$P$_2$. Our Density Functional Theory (DFT) and Monte Carlo-based calculations reveal an oscillating ground state magnetic order as a function of electron carrier density. The ground state is found to be A-AFM metal for x=0.056, 0.125 and 0.5 while it becomes ferromagnetic metal at x= 0.33, 0.67 and 1. Most importantly, we predict colossal anisotropic magnetoresistance in this compound for x=0.125 and 0.5. The underlying mechanism of anisotropic CMR in this compound looks similar to double exchange like due to the presence of a strong intra-site 4\textit{f}-5\textit{d} ferromagnetic exchange interaction and an itinerant electron in the hybridized conduction states. The oscillating ground state magnetic order and the enhancement of transition temperature (as high as 150K for x=0.67) as a function of electron carrier density offers a new avenue to tune the magnetotransport property in this compound and offers an excellent platform for designing future spintronics devices.