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We have studied room-temperature ferromagnetism (RTFM) in Sn1-xCoxO2 powders and films fabricated by the sol-gel method. Our X-ray diffraction, high-resolution transmission microscopy, and X-ray photoelectron spectroscopy results show that all the samples have a pure rutile structure, and Co ions have a chemical valence of 2+. In addition, the magnetic moment per Co ion drops rapidly with the increase of Co content. Interestingly, Sn1-xCoxO2 films spin-coated on a Si (111) substrate have much larger magnetic moment than powder samples, because film samples have larger domain volumes, which may induce stronger long-range magnetic exchange coupling. [ABSTRACT FROM AUTHOR]

A series of (Fe65Co35)x(B2O3)1-x nano-granular films with different metal volume fractions x were fabricated by magnetron sputtering. High resolution transmission electron micrographs show that the film consists of bcc Fe65 Co35 particles uniformly embedded in an amorphous insulating B2O3 matrix with particle size around a few nanometers. With the decrease in x from 0.66 to 0.55, the films exhibit coercivity HC not exceeding 16 Oe, along with high resistivity. Especially for the sample with x = 0.61, coercivities in hard and easy axes are 3 and 13.4 Oe, respectively, 4πMS = 12.5 kG, and ρ reaches 2.38 × 103 μΩ · cm. The dependence of complex permeability μ = μ′ - jμ′ on frequency shows that the real part μ′ is more than 170 below 1.5 GHz and ferromagnetic resonance frequency reaches 2.65 GHz. The good soft magnetic property is ascribed to the exchange coupling among magnetic granules. The investigation of the ΔM-H curve evidences the existence of this inter-granule interaction. [ABSTRACT FROM AUTHOR]

Co-doped TiO2 system is one of the most promising candidates for room-temperature ferromagnetic semiconductors. However, the origin on its room-temperature ferromagnetism has not been totally understood. In this paper, Co0.04Ti0.96 O2 powders were fabricated by sol-gel method. The structure and magnetic properties were investigated at different annealing conditions systematically with emphasis on the influence of oxygen pressure. Pure anatase structure was acquired for all samples annealed at 450 °C for 1 h except the one annealed in oxygen flow. The samples annealed in air exhibit evident room-temperature ferromagnetism with small magnetic moment of 0.029 μB per Co atom, while the samples annealed in vacuum have strong ferromagnetism with larger magnetic moment of 1.18 μB per Co atom. Zero field spin echo nuclear magnetic resonance spectrum of 59Co detected the existence of Co clusters in the latter samples, implying that the strong ferromagnetism in these samples annealed in vacuum comes from the Co clusters and is not the intrinsic property of the Co0.04Ti0.96O2 materials. [ABSTRACT FROM AUTHOR]