[en] A new model is proposed for ferromagnetism associated with defects in the bulk or at the surface of nanoparticles. The basic idea is that a narrow, structured local density of states N_s(E) is associated with the defects, but the Fermi level (which may lie above or below a mobility edge) will not normally coincide with a peak in N_s(E). However, if there is a local charge reservoir, such as a dopant cation coexisting in two different charge states or a charge-transfer complex at the surface, then it may be possible for electron transfer to raise the Fermi level to a peak in the local density of states, leading to Stoner splitting of N_s(E). Spontaneous Stoner ferromagnetism can arise in percolating defect-rich regions, such as the nanoparticle surface. The charge-transfer ferromagnetism model may be applicable to a wide range of nanoparticles and thin films of dilute magnetic oxides have previously been regarded as dilute magnetic semiconductors

[en] Hexagonal CoO thin films on (0 0 0 1) Al₂O₃ and ZnO are prepared by off-axis and on-axis pulsed laser deposition. The structural properties were studied by in situ reflection high-energy electron diffraction and ex situ x-ray diffraction. The magnetic properties of the films depend on the mode of growth. The films grown in a normal geometry are a mixture of Co₃O₄ and CoO and show ferromagnetism at room temperature, whereas the films grown off-axis are single phase and present a Curie-Weiss behaviour. Wurtzite CoO does not order magnetically because the antiferromagnetic Co²⁺-O^2--Co²⁺ superexchange is geometrically frustrated. It is proposed that defective Co₃O₄ in thin films is ferrimagnetic, due to the appearance of high spin Co³⁺ on B sites

[en] Oxides with the delafossite structure (space group R3-bar m) are of interest as wide-bandgap semiconductors, and as multiferroics. Well oriented c-axis films of CuCrO₂ and CuCr_0.9Mg_0.1O₂ have been produced on c-cut sapphire by PLD at elevated temperatures (650 ⁰C). The lattice parameters for CuCrO₂ are a = 299.6 pm and c = 1719.7 pm. The end member is insulating at room temperature with ρ ∼> 1000 Ω m whereas the Mg-doped oxide is a degenerate p-type semiconductor with ρ ∼ 1.5 x 10^-4 Ω m. There is a resistivity anomaly at T_N. A large negative magnetoresistance, which reaches its maximum value (∼ 300 %) in 14 T at about 2 K, persists throughout the temperature range where magnetic short range order is significant.

[en] Single crystals of the metallically degenerate fully magnetic semiconductors CuCr₂Se₄ and CuCr₂Se₃Br have been prepared by the Chemical Vapour Transport method, using either Se or Br as transport agents. The high-quality, millimetre-sized, octahedrally faceted, needle- and platelet-shaped crystals are characterised by means of high field magnetotransport (μ₀H≤ 14 T) and Point Contact Andreev Reflection. The relatively high spin polarisation observed |P|>0.56, together with the relatively low minority carrier effective mass of 0.25 m_e, and long scattering time  10⁻¹³ s, could poise these materials for integration in low- and close-to-room temperature minority injection bipolar heterojunction transistor demonstrations

No abstract available

[en] Heteroepitaxial growth of BaSnO₃ and Ba_1−xLa_xSnO₃ (x = 7%) lanthanum doped barium stannate thin films on different perovskite single crystal (SrTiO₃ (001) and SmScO₃ (110)) substrates has been achieved by pulsed laser deposition under optimized deposition conditions. X-ray diffraction measurements indicate that the films on either of these substrates are relaxed due to the large mismatch and present a high degree of crystallinity with narrow rocking curves and smooth surface morphology while analytical quantification by proton induced X-ray emission confirms the stoichiometric La transfer from a polyphasic target, producing films with measured La contents above the bulk solubility limit. The films show degenerate semiconducting behavior on both substrates, with the observed room temperature resistivities, Hall mobilities, and carrier concentrations of 4.4 mΩ cm, 10.11 cm² V⁻¹ s⁻¹, and 1.38 × 10²⁰ cm⁻³ on SmScO₃ and 7.8 mΩ cm, 5.8 cm² V⁻¹ s⁻¹, and 1.36 × 10²⁰ cm⁻³ on SrTiO₃ ruling out any extrinsic contribution from the substrate. The superior electrical properties observed on the SmScO₃ substrate are attributed to reduction in dislocation density from the lower lattice mismatch

[en] Growth temperature plays a major role on the magnetic and structural properties of Co-doped ZnO thin films. Ferromagnetism is observed only in films grown at temperatures within a narrow range around 450 deg. C . Metallic Co is detected in 40-300 nm thick films, and the estimated content is compatible with the magnetic moment observed

[en] The properties of molecular beam epitaxy-grown InSb_1−xBi_x alloys are investigated. Rutherford backscattering spectrometry shows that the Bi content increases from 0.6% for growth at 350 °C to 2.4% at 200 °C. X-ray diffraction indicates Bi-induced lattice dilation and suggests a zinc-blende InBi lattice parameter of 6.626 Å. Scanning electron microscopy reveals surface InSbBi nanostructures on the InSbBi films for the lowest growth temperatures, Bi droplets at intermediate temperatures, and smooth surfaces for the highest temperature. The room temperature optical absorption edge was found to change from 172 meV (7.2 μm) for InSb to ∼88 meV (14.1 μm) for InSb_0.976Bi_0.024, a reduction of ∼35 meV/%Bi