Spectroscopic study of Zn1−xCoxO thin films showing intrinsic ferromagnetism

Dilute magnetic semiconductors are widely studied due to their potential applications in spin-resolved electronics. We report the direct evidences of intrinsic ferromagnetism in the primarily ferromagnetic ZnO:Co thin films using near-edge X-ray absorption fine structure (NEXAFS) and soft X-ray magnetic circular dichroism (XMCD). The single phase Zn1−xCoxO thin films with nominal compositions (0.00 ≤ x ≤ 0.15) were synthesized by a spray pyrolysis technique, which exhibit room temperature ferromagnetism as revealed by alternating gradient force magnetometer (AGFM) measurements. The spectroscopic measurements indicate that most of Co dopants have substituted for Zn sites in ZnO matrix and they are present in divalent Co2+ (d7) state with tetrahedral symmetry according to the atomic multiplet calculations. The O 1s NEXAFS spectra suggest strong hybridization between O 2p and Co 3d electrons within ZnO matrix. The Co 2p XMCD measurements rule out the magnetism due to the presence of Co clusters, and show that Co–O–Co bonding provides localized magnetic moments leading to ferromagnetism. - Highlights: • We have studied the electronic and magnetic properties of ZnO:Co thin films. • The study uses X-ray absorption and magnetic circular dichroism spectroscopies. • Co dopants substitute for Zn sites in ZnO matrix and are divalent Co2+. • Measurements indicate Co clusters are not formed. • Co–O–Co bonding provide localized magnetic moments leading to ferromagnetism