Magnetization and Anisotropy of Cobalt Ferrite Thin Films

The magnetization of thin films of cobalt ferrite frequently falls far below the bulk value of 455 kAm-1, which corresponds to an inverse cation distribution in the spinel structure with a significant orbital moment of about 0.6 muB that is associated with the octahedrally-coordinated Co2+ ions. The orbital moment is responsible for the magnetostriction and magnetocrystalline anisotropy, and its sensitivity to imposed strain. We have systematically investigated the structure and magnetism of films produced by pulsed-laser deposition on different substrates (TiO2, MgO, MgAl2O4, SrTiO3, LSAT, LaAlO3) and as a function of temperature (500-700 C) and oxygen pressure (10-4 - 10 Pa). Magnetization at room-temperature ranges from 60 to 440 kAm-1, and uniaxial substrate-induced anisotropy ranges from +220 kJm-3 for films on deposited on MgO (100) to -2100 kJm-3 for films deposited on MgAl2O4 (100), where the room-temperature anisotropy field reaches 14 T. No rearrangement of high-spin Fe3+ and Co2+ cations on tetrahedral and octahedral sites can reduce the magnetization below the bulk value, but a switch from Fe3+ and Co2+ to Fe2+ and low-spin Co3+ on octahedral sites will reduce the low-temperature magnetization to 120 kAm-1, and a consequent reduction of Curie temperature can bring the room-temperature value to near zero. Possible reasons for the appearance of low-spin cobalt in the thin films are discussed. Keywords; Cobalt ferrite, thin films, pulsed-laser deposition, low-spin Co3+, strain engineering of magnetization

High-Performance Atomically-Thin Room-Temperature NO2 Sensor.

The development of room-temperature sensing devices for detecting small concentrations of molecular species is imperative for a wide range of low-power sensor applications. We demonstrate a room-temperature, highly sensitive, selective, stable, and reversible chemical sensor based on a monolayer of the transition-metal dichalcogenide Re0.5Nb0.5S2. The sensing device exhibits a thickness-dependent carrier type, and upon exposure to NO2 molecules, its electrical resistance considerably increases or decreases depending on the layer number. The sensor is selective to NO2 with only minimal response to other gases such as NH3, CH2O, and CO2. In the presence of humidity, not only are the sensing properties not deteriorated but also the monolayer sensor shows complete reversibility with fast recovery at room temperature. We present a theoretical analysis of the sensing platform and identify the atomically sensitive transduction mechanism

Systematic review and meta-analysis of the diagnostic accuracy of ultrasonography for deep vein thrombosis

Background Ultrasound (US) has largely replaced contrast venography as the definitive diagnostic test for deep vein thrombosis (DVT). We aimed to derive a definitive estimate of the diagnostic accuracy of US for clinically suspected DVT and identify study-level factors that might predict accuracy. Methods We undertook a systematic review, meta-analysis and meta-regression of diagnostic cohort studies that compared US to contrast venography in patients with suspected DVT. We searched Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club, and citation lists (1966 to April 2004). Random effects meta-analysis was used to derive pooled estimates of sensitivity and specificity. Random effects meta-regression was used to identify study-level covariates that predicted diagnostic performance. Results We identified 100 cohorts comparing US to venography in patients with suspected DVT. Overall sensitivity for proximal DVT (95% confidence interval) was 94.2% (93.2 to 95.0), for distal DVT was 63.5% (59.8 to 67.0), and specificity was 93.8% (93.1 to 94.4). Duplex US had pooled sensitivity of 96.5% (95.1 to 97.6) for proximal DVT, 71.2% (64.6 to 77.2) for distal DVT and specificity of 94.0% (92.8 to 95.1). Triplex US had pooled sensitivity of 96.4% (94.4 to 97.1%) for proximal DVT, 75.2% (67.7 to 81.6) for distal DVT and specificity of 94.3% (92.5 to 95.8). Compression US alone had pooled sensitivity of 93.8 % (92.0 to 95.3%) for proximal DVT, 56.8% (49.0 to 66.4) for distal DVT and specificity of 97.8% (97.0 to 98.4). Sensitivity was higher in more recently published studies and in cohorts with higher prevalence of DVT and more proximal DVT, and was lower in cohorts that reported interpretation by a radiologist. Specificity was higher in cohorts that excluded patients with previous DVT. No studies were identified that compared repeat US to venography in all patients. Repeat US appears to have a positive yield of 1.3%, with 89% of these being confirmed by venography. Conclusion Combined colour-doppler US techniques have optimal sensitivity, while compression US has optimal specificity for DVT. However, all estimates are subject to substantial unexplained heterogeneity. The role of repeat scanning is very uncertain and based upon limited data