Strongly enhanced magnetic moments of vanadium impurities in thin films of sodium and potassium

Thin quench-condensed films of Na and K are covered with 1/100 of a monolayer of V. Then the impurities are covered with several atomic layers of the host. The magnetization of the films is measured by means of the anomalous Hall effect. For V impurities on the surface of Na and K, a magnetic moment of 7 Bohr magnetons is observed. After coverage with the host, the V moment became 6.5 mu(B) for the Na host. These results contradict the favored atomic model (predicting 3/5 mu(B)) and the resonance model. A polarization of the alkali host appears to be the only resolution.     

Electron-beam deposition of vanadium dioxide thin films

Developing a reliable and efficient fabrication method for phase-transition thin-film technology is critical for electronic and photonic applications. We demonstrate a novel method for fabricating polycrystalline, switchable vanadium dioxide thin films on glass and silicon substrates and show that the optical switching contrast is not strongly affected by post-processing annealing times. The method relies on electron-beam evaporation of a nominally stoichiometric powder, followed by fast annealing. As a result of the short annealing procedure we demonstrate that films deposited on silicon substrates appear to be smoother, in comparison to pulsed laser deposition and sputtering. However, optical performance of e-beam evaporated film on silicon is affected by annealing time, in contrast to glass.     

Weak-localization and interaction effects in thin vanadium films

High resolution electrical resistance and transverse magnetoresistance measurements were performed on thin vanadium films. A logarithmic increase of the resistivity with decreasing temperature was observed at low temperature. The results are consistent with a two-dimensional weak localization and electron-electron interactions models.     

溶胶-凝胶VO2薄膜转换特性研究

利用溶胶凝胶法在SiO2Si衬底上沉积高取向的V2O5薄膜,在压强低于2Pa,温度高于400℃的条件下,对V2O5薄膜进行真空烘烤,获得了电阻率变化3个数量级以上、弛豫宽度为62℃的VO2多晶薄膜.以X射线衍射(XRD)、扫描电子显微镜(SEM)图和电阻率转换特性等实验结果为依据,详细分析了溶胶凝胶薄膜在真空烘烤时从V2O5向VO2的转化,它经历了从VnO2n+1(n=2,3,4,6)到VO2的过程.实验证明,根据选择合适的成膜热处理条件和真空烘烤条件是实现溶胶凝胶V2O5结构向VO2结构成功转换的关键 关键词： 溶胶-凝胶法 氧化钒薄膜 VO2膜转换特性     

Giant magnetoresistance of vanadium films with a surface magnetic superlattice

Giant (up to 68%) room-temperature magnetoresistance is observed in (110) V films on mica with a periodic system of 5–25 nm wide, thin (⩽10 nm) Co strips, separated by 1–2 nm gaps, grown on the films. The effect is observed only for samples in which the magnetization tilts out of the plane of the film. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 5, 346–349 (10 September 1996)     

High contrast optical switching in vanadium dioxide thin films

Thermochromic vanadium dioxide thin films prepared by radio-frequency sputtering exhibit controllable transmittance at 1550 nm with a dynamic range exceeding 10³. Efficient optical control with a laser beam at 532 nm is demonstrated with intensities as low as 3 W/cm². Optical switch-on times as short as 100 μs are reported.     

The influence of a static magnetic field on the fluctuation superconductivity

We study the influence of an external static magnetic field on the additional conductivity due to fluctuation superconductivity for bulk material and for thin films with the magnetic field normal to the film surfaces. Only a weak-coupling superconductor in the dirty limit is considered. This additional conductivity turns out to be anisotropic in general.     

Distortions of the magnetic structure of a thin antiferromagnetic layer in magnetic field

Distortions induced by an external magnetic field in the magnetic structure of a thin layer of a uniaxial collinear antiferromagnet with rough surfaces are studied using computer simulation. It is shown that, under certain conditions, the presence of atomic steps at the layer surfaces causes the antiferromagnetic layer to break up into domains. The character and magnitude of distortions are found for an arbitrary ratio of the distance between atomic steps to the order parameter correlation length. Original Russian Text ? A.I. Morosov, I.A. Morosov, A.S. Sigov, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 7, pp. 1228–1235.     

Numerical simulation of graphene in a magnetic field within the effective field theory

Monte Carlo simulation of graphene in an external magnetic field perpendicular to the plane of graphene has been reported. The calculations have been performed using the effective quantum field theory with a noncompact (3 + 1)-dimensional Abelian gauge field and (2 + 1)-dimensional Kogut-Susskind fermions. It has been revealed that the external magnetic field shifts the semimetal-insulator phase transition point toward higher dielectric constants of the substrate. The phase diagram of the semimetal-insulator phase transition has been plotted in the (dielectric constant of the substrate-magnetic field) plane.     

Exploring the 2D to 3D dimensionality crossover in thin iron films

The temperature dependence of the spontaneous magnetization of epitaxial iron films with a thickness ranging from d=20$d=20$ to 200 nm has been measured. The films are grown on GaAs (1 0 0) substrates which are covered by a 150 nm thick silver (1 0 0) buffer layer. For three-dimensional BCC iron it was observed already in 1929 that saturation of the spontaneous magnetization for T→0$T\to 0$ is perfectly described by a T² power law. On the other hand, for thin two-dimensional (2D) iron films a T^3/2 law has been established in many recent experimental investigations. In our iron films grown on diamagnetic silver, this dimensionality change occurs at a thickness between d=100$d=100$ and 200 nm. Comparison of the here-observed T^3/2 coefficients with those on iron films grown on paramagnetic tungsten (1 1 0) shows that the 2D interactions are ∼20 times larger in the films on tungsten. Recent results on Fe films which are grown directly on GaAs (1 0 0) confirm that the substrate has a very strong effect on the coefficient of the T^3/2 function, i.e. on the strength of the magnetic interactions in the films.     

Effects of spin paramagnetism on the magnetic field behavior of thin superconducting beryllium films

Tunneling measurements on thin superconducting Be in a parallel magnetic field show splitting of the quasiparticle states and other effects of Pauli paramagnetism with small spin-orbit scattering.     

Nanostructure and thermal-optical properties of vanadium dioxide thin films

A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing.     

氧化钒薄膜微观结构的研究

采用直流磁控反应溅射在Si(100)衬底上溅射得到(001)取向的V₂O₅薄膜.x射线衍射(XRD)、扫描电镜(SEM)和傅里叶变换红外光谱(FTIR)的结果表明，氧分压影响薄膜的成分和生长取向，在氧分压0.4Pa时溅射得到(001)取向的纳米V₂O₅薄膜，即沿c轴垂直衬底方向取向生长的薄膜.V₂O₅薄膜经过真空退火得到(001)取向的VO₂薄膜，晶体颗 关键词： 微观结构 氧化钒薄膜 择优取向 直流磁控溅射     

High field superconductivity in thin films

Thin films provide an ideal means for studying the role of spin paramagnetism in the theory of superconductivity. A review is given of the theoretical and experimental work available until now with respect to this problem. It includes a study of the excitation spectrum of thin films in a parallel magnetic field and the experimental evidence of Zeeman splitting of superconducting quasiparticles. The role of spin-orbit interaction is discussed in detail. The application of spin selective tunnelling is shown. Furthermore, it includes a study of the order of phase transition between the normal state and the paramagnetically limited superconducting state. A detailed discussion is given of the generalized Ginzburg-Landau equation including numerical evaluations. The applicability of Tinkham's formula is discussed, which is relevant for the determination of critical fields of arbitrary orientations to the film. Finally, account is given of the work which deals with the influence of spin paramagnetism on superconducting fluctuations. Recent experimental and theoretical work is described and discussed.     

Preparation and properties of vanadium dioxide thermochromic thin films

Deposition of vanadium dioxide and the study of its electrical and optical properties at varying deposition conditions have been presented. The materials have been deposited by reactive r.f. magnetron sputtering technique in Ar, O₂ ambient followed by annealing post-treatment. Electrical conductivity measurements indicate that oxygen pressure plays an important role in obtaining VO₂ and atP _{O 2}=2.4% stoichiometric VO₂ can be obtained. The deposition rate of oxides decreases with increasing O₂ pressure and the rate of VO₂ was about 130Å/min. Optical studies show that VO₂ films exhibit thermochromism and it has the potential application for energy efficient solar energy utilization.