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We demonstrate a semiconducting material, TiO 2−δ , with ferromagnetism up to 880 K, without the introduction of magnetic ions. The magnetism in these films stems from the controlled introduction of anion defects from both the filmsubstrate interface as well as processing under an oxygen-deficient atmosphere. The room-temperature carriers are n-type with n ∼ 3 × 10 17 cm −3 . The density of spins is ∼10 21 cm −3 . Magnetism scales with conductivity, suggesting that a double exchange interaction is active. This represents a new approach in the design and refinement of magnetic semiconductor materials for spintronics device applications.(Some figures in this article are in colour only in the electronic version)Recent research efforts on the growth of magnetically ordered semiconductor materials [1,2] have received great attention because of potential new applications in spintronics devices [3]. The rationale for this optimism is the plausibility of integrating properties of both magnetic and semiconductor materials in new devices [1] (e.g. spin diodes [3-6] and spin-FETs [7]). Recent research has focused on dilute magnetic semiconductors (DMS) which were synthesized by introducing magnetic ions (e.g. Mn, Co, Fe, and etc) into conventional III-V [1, 2] and II-VI type semiconductors [8,9] or wide bandgap semiconductors including ZnO and TiO 2 [8][9][10][11][12][13]. Also, ferromagnetism was induced in films of hafnium dioxide, HfO 2 , deposited by pulsed laser deposition (PLD) on sapphire substrates and attributed to defect doping [10][11][12]. Bulk HfO 2 is intrinsically non-magnetic and electrically insulating. This report has created intense

Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 4 kOe and maximum energy products greater than 20 KJ/m 3 . Consisting of Co 3 C and Co 2 C phases, the ratio of phase volume, particle size, and particle morphology all play important roles in determining permanent magnet properties. Further, the acicular particle shape provides an enhancement to the coercivity via dipolar anisotropy energy as well as offering potential for particle alignment in nanocomposite cores. While Curie temperatures are near 510K at temperatures approaching 700 K the carbide powders experience an irreversible dissociation to metallic cobalt and carbon thus limiting operational temperatures to near room temperature.2

Next generation magnetic microwave devices require ferrite films to be thick ͑Ͼ300 m͒, self-biased ͑high remanent magnetization͒, and low loss in the microwave and millimeter wave bands. Here we examine recent advances in the processing of thick Ba-hexaferrite ͑M-type͒ films using pulsed laser deposition ͑PLD͒, liquid-phase epitaxy, and screen printing. These techniques are compared and contrasted as to their suitability for microwave materials processing and industrial production. Recent advances include the PLD growth of BaM on wide-band-gap semiconductor substrates and the development of thick, self-biased, low-loss BaM films by screen printing.

Mn ferrite (MnFe(2)O(4)) nanoparticles, having diameters from 4 to 50 nm, were synthesized using a modified co-precipitation technique in which mixed metal chloride solutions were added to different concentrations of boiling NaOH solutions to control particle growth rate. Thermomagnetization measurements indicated an increase in Néel temperature corresponding to increased particle growth rate and particle size. The Néel temperature is also found to increase inversely proportionally to the cation inversion parameter, delta, appearing in the formula (Mn(1-delta)Fe(delta))(tet)[Mn(delta)Fe(2-delta)](oct)O(4). These results contradict previously published reports of trends between Néel temperature and particle size, and demonstrate the dominance of cation inversion in determining the strength of superexchange interactions and subsequently Néel temperature in ferrite systems. The particle surface chemistry, structure, and magnetic spin configuration play secondary roles.

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The ferromagnetism induced by the intrinsic point defects in wurtzite zinc oxide is studied by using ab initio calculation based on density functional theory. The calculations show that both oxygen interstitial and zinc vacancy may induce ferromagnetism into this material. The calculations also show that zinc oxide with oxygen interstitial may be a ferromagnetic semiconductor. Based on the simplified electronic configuration of the defect molecules, we explain the total magnetic moment, electronic structure, and ferromagnetism.

Next generation magnetic microwave devices require ferrite films to be thick ͑Ͼ300 m͒, self-biased ͑high remanent magnetization͒, and low loss in the microwave and millimeter wave bands. Here we examine recent advances in the processing of thick Ba-hexaferrite ͑M-type͒ films using pulsed laser deposition ͑PLD͒, liquid-phase epitaxy, and screen printing. These techniques are compared and contrasted as to their suitability for microwave materials processing and industrial production. Recent advances include the PLD growth of BaM on wide-band-gap semiconductor substrates and the development of thick, self-biased, low-loss BaM films by screen printing. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2165145͔ INTRODUCTIONDriven by radar electronics and wireless technologies, the next generation of magnetic microwave devices ͑isola-tors, filters, phase shifters, and circulators and related components͒ will be planar, self-biased, and low loss, and operate well beyond the performance metrics of today's devices. Self-biasing is an important property that eliminates the need for a biasing field that is provided by a comparatively large permanent magnet. The elimination of this magnet is an essential step in making these devices smaller and planar. Integration with semiconductor devices continues to be a desirable property that requires ferrite fabrication techniques to be compatible with complementary metal-oxide semiconductor ͑CMOS͒ processing. This is a difficult task considering that most ferrite fabrication techniques require temperatures Ͼ900°C to produce high-quality films.In order to achieve these goals, magnetic materials must possess high saturation magnetization ͑4M s ͒, high remanent magnetization ͑M r ͒, adjustable magnetic anisotropy fields ͑H A ͒, low microwave losses ͓i.e., low ferromagnetic resonance ͑FMR͒ linewidths ⌬H FMR ͔, and for many applications, have the easy axis of magnetization perpendicular to the film plane ͑i.e., perpendicular magnetic anisotropy͒. In physical terms, the films should be thick ͑Ͼ300 m͒, dense ͑low levels of porosity that are responsible for added microwave loss͒, and pure phase. For many applications the microstructure should possess a strong crystallographic orientation, although true epitaxy is not required.In this paper, we focus on recent advances made in the processing of Ba hexaferrite films for applications in microwave and millimeter-wave devices, with special emphasis on circulator devices. We will compare and contrast different film processing technologies including pulsed laser deposition ͑PLD͒, liquid-phase epitaxy ͑LPE͒, and screen printing.Ba ͑M-type͒ hexaferrite ͑henceforth BaM͒ has the magnetoplumbite structure and a stoichiometry of BaFe 12 O 19 . This structure has 32 atoms/ f.u. and 64 atoms in a single unit cell ͑see Fig. 1͒. One property of this compound that is of particular value in microwave device design is the strong uniaxial anisotropy with the easy direction being along the c axis ͑H A ϳ 17 000 Oe͒.1,2 The high magnetic anisotropy field can b...