Giant moment and magnetic anisotropy in Co-doped ZnO films grown by pulse-injection metal organic chemical vapor deposition

Abstract

We report on large magnetic moments of up to 18.9μB∕Co in Co-doped ZnO films grown by pulse-injection metal organic chemical vapor deposition. The magnetic moment saturates easily in perpendicular magnetic fields and is considerably reduced when the magnetic field is applied parallel to the film plane. The saturation moment is largest for a small Co doping concentration of 1% and persists up to a temperature well above 900K. These extraordinary magnetic attributes cannot be explained by the spin-only moment of Co2+ ions or Co cluster, but suggest the formation of orbital states in a defect-related impurity band.

Magnetic anisotropy in nanocrystalline Co-doped ZnO thin films

“…Similar trend was observed in the Zn 1Àx Co x O films by Zukova et al [5], and Khare et al [20]. When the Co concentration increases the intensity of the (0 0 2) peak decreases with increase in full width at half maximum (FWHM).…”

“…Coey et al predicted that the magnetic anisotropy is presumably due to new type of ferromagnetism-related defects at the film-substrate interface [35]. The recent observation refers that the origin of magnetic anisotropy may possibly arise from orbital states in a defect-related impurity band [5]. It is also argued that the magnetization anisotropy is due to the trapping of a large number of electrons in orbital states could facilitate an increase of the spin-orbit interaction strength due to symmetry breaking at lattice defects [36].…”

“…Identification of a DMS material exhibiting room-temperature (RT) ferromagnetism is thus essentially very important for the success of making spintronicsbased devices. It is predicted theoretically [3,4] that an oxide-based high-T c DMS can be fabricated with transition metal (TM)-doped ZnO [5][6][7]. Although there are quite a lot of reports available on growth and property study of TM-doped ZnO thin films, a review of literature shows contrary results concerning ferromagnetic behavior in Co-doped ZnO as well as about the underlying mechanism.…”

Experimental and theoretical studies of hydroxyl-induced magnetism in TiO nanoclusters

“…32 A power-law decay is reported for the magnetic moment of ZnO during storage in air. 33 It is suggested that these relaxations can be ascribed to Arrhenius type behavior with a distribution of diffusion-site energies. 34 Detailed electronic structure calculations are still necessary to clarify the role of hydroxyls for a particular oxide.…”

Room temperature ferromagnetism in vacuum-annealed TiO2 thin films

“…Beginning with the claim of room temperature ferromagnetism in laser-ablated films of Co-doped anatase TiO 2 [4], there have been many studies on development of ferromagnetic order at room temperature in a range of transition metal doped semiconducting oxides, including TiO 2 , ZnO, SnO 2 and In 2 O 3 [5][6][7][8][9]. This ferromagnetism typically persists above T ¼ 300 K, and the moment per transition metal dopant can exceed the spin-only value in some cases [10][11][12]. However, it has been observed that the magnetic properties are extremely sensitive to sample preparation and measurement techniques, leading to concerns that in many cases ferromagnetism may not be intrinsic but arises from impurity clusters.…”