Origin of ferromagnetism in Mn and Cr co-doped CdTe thin films: An experimental and theoretical study

Abstract

Cadmium telluride (CdTe) is a promising semiconductor for spintronic applications, especially when doped with transition metal (TM) ions. We report here on the structural, electronic, and magnetic properties of Mn and Cr co-doped CdTe, i.e., Cd1−x−yMnxCryTe (x = 0.05, 0.10, 0.15; y = 0, 0.03), thin films grown on (001) GaAs substrates via radio frequency sputtering. High-resolution x-ray diffraction confirms that doping preserves the zinc-blende cubic structure without secondary phases. Atomic force microscopy reveals uniform film morphology. Magnetization measurements and element-specific soft x-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) indicate ferromagnetic ordering induced by Mn and Cr substitution at Cd sites. XMCD measurement reveals that for Mn, the spin, orbital, and total magnetic moments are 0.20–0.52 μB, 0.01–0.05 μB, and 0.19–0.48 μB per Mn, respectively. For Cr, the corresponding values are 0.97–1.01 μB, 0.32–0.41 μB, and 1.30–1.40 μB per Cr atom. The enhanced spin contribution is attributed to the strong sp-d exchange interaction. A significant increase in the total magnetic moment is observed upon Cr co-doping, resulting in a paramagnetic (Mn-only) to ferromagnetic transition due to double-exchange interactions. In Mn and Cr co-doped CdTe, the Mn–Cr interactions enhance magnetic coupling and modify the electronic structures through the strong sp-d exchange interaction between the 3d electrons of Mn2+ and Cr2+ and the host's carrier, stabilizing room temperature ferromagnetism. The first-principles density functional theory calculations using Local Density Approximation  + U corroborate experimental findings and predict the half-metallic character in these doped films. The results demonstrate the role of TM co-doping in tailoring ferromagnetism in CdTe, with potential implications for spintronic device applications.