Magnetization and magnetic circular dichroism of La0.7Sr0.3MnO3/YSZ polycrystalline films

The magnetic and magneto-optical properties as well as the surface morphology and structure of La_0.7Sr_0.3MnO₃ polycrystalline films of different thicknesses have been investigated. It has been shown that films have a rough surface with a characteristic in-plane linear dimension of ～30 nm, and crystallites with linear dimensions of 10–20 nm are randomly oriented in the plane. The temperature and field dependences of the magnetization of the films indicate their magnetic inhomogeneity. The magnetic circular dichroism spectra contain a number of bands, one of which at 2.4 eV is explained by the contribution of conduction electrons.     

在蓝宝石上生长CeO2 缓冲层的原位双温工艺法及Tl-2212薄膜的技术改进

报道了在蓝宝石衬底上制备CeO₂缓冲层的原位双温工艺法及其对Tl₂Ｂa₂CaCu₂Ｏ₈（Tl-2212）薄膜超导特性的影响．XPS和AFM测试结果表明,采用原位双温工艺法制备缓冲层,具有工艺简单,薄膜表面光滑,衬底材料原子扩散量少等特点．在先驱膜的高温后退火过程中,40 nm厚的CeO₂薄膜就能有效地阻挡衬底材料对超导薄膜底层的扩散．随后制备厚度为530 nm的Tl-2212 关键词： Tl-2212超导薄膜 蓝宝石 氧化铈缓冲层 原位双温工艺法     

Atomic force microscopy of the supramolecular organization and strength properties of ultrathin polysiloxane block copolymer films

Ultrathin films of polysiloxane block copolymers and their composites with modifying additives of the C₆₀ fullerene have been studied using atomic force microscopy. It has been revealed that, independently of the concentration of the additives, the surface relief of the films has an ordered structure with a period of approximately 35 nm, which is associated with the presence of a spatial network of rigid block domains of ladder phenylsilasesquioxane in the block copolymer. The mechanical properties of the films have been determined from indentation tests of their surface layers. Reliable quantitative measurements have been performed with specially fabricated spherical indenters of the calibrated submicron radius of curvature. The obtained values of the strength parameters correlate with the data derived from standard physical and mechanical tests of thick films. It has been found that the addition of the C₆₀ fullerene at a level of 0.01% significantly improves the elasticity of the surface layers of the block copolymer.     

Magnetic properties of field-annealed FeCo thin films

Fe₅₀Co₅₀ thin films with thickness of 30 and 4 nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350 °C for times between 20 and 120 min, under a static magnetic field of 100 Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4 nm display lower coercive fields with respect to the 30 nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30 nm thick films.     

外加磁场对射频磁控溅射制备铝掺杂氧化锌薄膜影响的研究

利用射频磁控溅射法制备了铝掺杂氧化锌(AZO)透明导电薄膜,在传统的磁控溅射系统中引入外加磁场,研究了外加磁场对AZO薄膜沉积速率、形貌结构及光电特性的影响.研究结果表明,外加磁场后薄膜的沉积速率从不加磁场的13.04 nm/min提高到了19.93 nm/min;外加磁场后薄膜表面平整致密、颗粒大小均匀,结晶质量较高,而不加磁场薄膜表面形貌呈蠕虫状,薄膜质量较差.溅射时间为90 min时,外加磁场前后AZO薄膜方阻分别为30.74?/和12.88?/.外加磁场对薄膜可见光透过率影响不大,但使薄膜的吸收边蓝移现象更明显.运用ansys软件对磁控溅射二维磁场分布模拟后发现,外加磁场提高了靶上方横向磁场强度,改善了磁场分布的均匀性,加强了磁场对电子的磁控作用,提高了靶电流,是AZO薄膜的溅射速率、光电性能和形貌结构得到提高和优化的原因.     

Surface electromagnetic waves in thin-layer biaxial structure in a magnetic field

The conditions for the existence of surface electromagnetic waves at the planar interface between a homogeneous medium (vacuum) and a thin-layer periodic structure consisting of alternating semiconductor and dielectric layers in an external magnetic field have been investigated. This structure represents an optically biaxial crystal with the effective permittivity tensor components dependent both on the geometric parameters of the structure and on the physical characteristics (magnetic field strength, frequency, and thicknesses of the layers). It has been shown that the propagation of surface electromagnetic waves localized near the interface can occur in the thin-layer biaxial structure within specific ranges of frequencies and external magnetic field strengths.     

Peculiarities of electric polarization in bi-layered longitudinally magnetized ferrromagnetic film

Electric polarization arising in a vicinity of magnetic inhomogenety in longitudinally magnetized ferromagnetic films has been considered. A variety of polarization transformations induced by external magnetic field have been studied. It has been demonstrated that electric polarization can change continuously or with a jump-like character depending on intrinsic, mainly anisotropic properties of the layers, the direction and the value of external magnetic field.     

Effect of Co layer thickness on structural and magnetic properties of C/Co/C films

Granular C/Co/C films have been prepared by magnetron sputtering from C and Co onto glass substrates at room temperature and subsequent in situ annealing. It has been found that the structure and magnetic properties of the C/Co/C films depend strongly on the Co layer thickness. Vibrating sample magnetometer measurements indicate that the in-plane coercivities reach maximum in 20 nm Co thickness of both as-deposited and annealed films. The squareness ratio of annealed films was more than 0.8. X-ray diffraction shows that majority Co nanograins are formed as the hexagonal-close-packed (HCP) structure in 20 nm Co thickness with annealing at 400 °C. Scanning probe microscope was used to scan surface morphology and magnetic domain structures. The values of the surface roughness were lower than 0.6 nm in all annealed samples. The average magnetic cluster size was estimated to be about 10 nm in annealed 20 nm Co thickness films.     

On the phenomena occurring at the interface between iron and iron–platinum thin films

FePt films were rf sputtered at room temperature and 550?C on MgO monocrystalline substrates. Room temperature films were post-annealed at 550?C. The high temperature growth induces a tetragonal distortion of the structure with the formation of L1₀-FePt phase. Soft iron layers, with different thickness, were e-beam deposited on these hard films. The phenomena occurring at the interface have been analysed and connected with the final magnetic behaviour of the system. It has been found that a strong exchange coupling between soft and hard layers has been established through the formation of an interfacial layer constituted by FePt small particles.     

Effect of the number of iron oxide nanoparticle layers on the magnetic properties of nanocomposite LbL assemblies

Aqueous colloidal suspension of iron oxide nanoparticles has been synthesized. Z-potential of iron oxide nanoparticles stabilized by citric acid was −35±3 mV. Iron oxide nanoparticles have been characterized by the light scattering method and transmission electron microscopy. The polyelectrolyte/iron oxide nanoparticle thin films with different numbers of iron oxide nanoparticle layers have been prepared on the surface of silicon substrates via the layer-by-layer assembly technique. The physical properties and chemical composition of nanocomposite thin films have been studied by atomic force microscopy, magnetic force microscopy, magnetization measurements, Raman spectroscopy. Using the analysis of experimental data it was established, that the magnetic properties of nanocomposite films depended on the number of iron oxide nanoparticle layers, the size of iron oxide nanoparticle aggregates, the distance between aggregates, and the chemical composition of iron oxide nanoparticles embedded into the nanocomposite films. The magnetic permeability of nanocomposite coatings has been calculated. The magnetic permeability values depend on the number of iron oxide nanoparticle layers in nanocomposite film.     

Effect of annealing in an external magnetic field on the microstructure and magnetic properties of the Fe/FePt/Pt multilayer system

The effect of annealing in an external magnetic field applied perpendicular to the plane of the film on the kinetics of Ll ₀ phase transformation of the microstructure and the magnetic properties of the Fe(2 nm)/FePt(20 nm)/Pt(2 nm) multilayer system has been investigated. The relations between the hysteresis loop shape, magnetic correlation length, and structural disorders, which are characteristic of magnetic information carriers, have been analyzed. It has been found that the annealing of the Fe(2 nm)/FePt(20 nm)/Pt(2 nm) multilayer system at a temperature of 470°C in an external magnetic field of 3500 Oe, which is applied perpendicular to the film plane, leads to the formation of a face-centered tetragonal structure of the Ll ₀ phase in the FePt film, which is characterized by the high coercivity H _c , the (001) preferred texture, the magnetic anisotropy perpendicular to the film plane, small sizes of FePt grains in the film, and weak exchange coupling between the particles. The energy of the external magnetic field encourages the process of transformation of the FePt film into the Ll ₀ phase. Thus, a method has been developed for fabricating multilayer films based on the FePt Ll ₀ phase with the parameters necessary for information carrier materials with perpendicular-type magnetic recording.     

Magnetic and Mössbauer studies of Fe/Mo multilayered thin films

Fe(x)/Mo(y), multilayered thin films (MLF) with y=7.0 nm and x=0.7, 1.3, 2.6, 3.6, 13.0 nm were fabricated by radio frequency (RF) sputtering. X-ray diffraction evidences that these films have a good periodicity and bcc structure for both Fe and Mo layers. Mössbauer spectra at room temperature (RT) are used to investigate the structure and the local magnetic properties of the interfaces between Fe and Mo layers. It is found that the interfaces present alloying features, i.e. the Fe atoms are randomly substituted by Mo atoms. Magnetic anisotropy which forces magnetic moments to lie in the film plane and reduced magnetic moments in interface region were observed. The specific magnetization of the films exhibits a BT^3/2 dependence with very large values of B which can be attributed to the distribution of exchange interaction in the interfaces.     

Photoinduced formation and aggregation of silver nanoparticles at the surface of carboxymethylcellulose films

Formation and aggregation of photolytic silver nanoparticles at the surface of silver salt of carboxymethylcellulose films (CMCAg films) have been investigated. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize silver nanoparticles at the film surface. When the CMCAg films were irradiated with UV light in wet air at room temperature for 30–60 min, silver nanoparticles of ca. 10 nm size were formed at the irradiated surface. According to the FE-SEM observation, the growth of the particle diameter and aggregation of nanoparticles took place after prolonged irradiation, and finally, the irradiated side of the film surface was densely covered with the silver nanoparticles of ca. 35 nm size. Chemical composition analysis by the XPS measurements has confirmed the increase in the atomic concentration of silver with irradiation time. It is suggested that silver atoms and clusters can move in the film and precipitate at the irradiated surface.     

Influence of the microcrystalline structure on the magnetic properties of ferromagnetic films and structures on their base

This paper presents the results of investigating the crystal structure of thin films of the Co₄₀Fe₆₀ composition obtained by magnetron sputtering on their magnetic properties and properties of ferromagnetic nanostructures formed from these films using the optical and electron lithography. It has been found experimentally that magnetic properties of the structures depend on the crystalline-grain sizes, which can be controlled by means of deposition of additional buffer layers of various materials ～1 nm thick on the substrate under the ferromagnetic film. It has been shown that the crystallite size can be the main factor that determines the minimal lateral sizes of the structures with specified magnetic properties, which are formed from thin ferromagnetic films.     

The magnetic field dependence of the PEM effect in melt-grown InSb thin layers

The room temperature dependence of the PEM effect on magnetic field has been measured in intrinsic, melt-regrown layers of InSb of thickness from 1 to 10 μm. When illuminated on the surface of higher recombination velocity (the back surface of the InSb layer) the samples showed an anomalous magnetic field dependence of the PEM effect. This was manifested in most of the samples as a sign reversal in the PEM voltage, from a negative voltage in weak magnetic fields to a positive voltage in strong fields. Since, theoretically, such a PEM voltage dependence might result from a strong dependence of the bipolar diffusion length L on the magnetic field H, several scattering mechanisms have been investigated to find the strongest dependence of L = L(H) in InSb layers. It has been found that the dependence L = L(H) could in no case be responsible for the experimental magnetic field dependence of the PEM effect. Good agreement between theory and experiment is reached if a magnetic field-dependent surface recombination velocity at the InSb-substrate interface is postulated. The shape of the dependence which gave the best fitting of theoretical to experimental results is given.     

强磁场对不同厚度Fe-Ni纳米多晶薄膜的生长过程及磁性能的影响

有无6 T强磁场条件下, 利用分子束气相沉积方法制备了21 nm和235 nm厚的Fe-Ni纳米多晶薄膜. 研究发现, 0 T时, 21 nm厚的薄膜是晶粒堆叠而成, 晶粒尺寸为6–7 nm; 6 T时, 21 nm厚的薄膜首先在基片表面形成了晶粒相互连接的5 nm平坦层, 晶粒沿基片表面拉长, 随后以6–7 nm尺寸的晶粒堆叠而成; 0 T时, 235 nm厚度的薄膜生长初期平均晶粒尺寸为3.6 nm, 生长中期平均晶粒尺寸为5.6 nm, 生长末期薄膜近似柱状方式生长, 晶粒沿生长方向拉长; 6 T时, 235 nm厚度的薄膜在基片表面也形成了晶粒相互连接的5 nm平坦层, 晶粒沿基片表面拉长, 随后以尺寸均匀的6.1 nm晶粒堆叠而成; 而且, 6 T强磁场使得不同厚度薄膜的面外与面内矫顽力都降低.     

Resonance modes of layered ferromagnets in a transverse magnetic field

Intensities and positions of resonance lines are calculated for the ferromagnetic resonance spectra of multilayer ferromagnetic films in a magnetic field oriented normally to the film surface. It is shown that the positions of spectral lines depend on the number of ferromagnetic layers, while the line intensities are determined by the phase shift between the oscillations of the magnetic moments of neighboring layers. A qualitative comparison is carried out between the results of calculations and the spectra observed in experiments.     

Properties of CoPt ferromagnetic layers for application in spin light-emitting diodes

The magnetic properties of Co₄₅Pt₅₅ films deposited by electron-beam evaporation in vacuum have been studied. The measurements of the Faraday and Kerr magnetooptical effects confirm the presence of the easy-magnetization axis perpendicular to the Co₄₅Pt₅₅ surface. It is shown that the perpendicular magnetic anisotropy and the residual magnetization are retained at 300 K for a long time. The magnetic characteristics of the Co₄₅Pt₅₅ layer surface have been studied by magnetic force microscopy, and “circular” mobile magnetic structures have been detected. The spin light-emitting diodes based on In(Ga)As/GaAs heteronanostructures with Co₄₅Pt₅₅ contact layers were fabricated. These diodes emit circularly-polarized light in the absence of an external magnetic field.     

Magnetization-orientation dependence of the superconducting transition temperature in the ferromagnet-superconductor-ferromagnet system: CuNi/Nb/CuNi

The superconducting critical temperature (T(c)) of ferromagnet-superconductor-ferromagnet systems has been predicted to exhibit a dependence on the magnetization orientation of the ferromagnetic layers such that T(AP)(c)>T(P)(c) for parallel (P) and antiparallel (AP) configurations of the two ferromagnetic layers. We have grown CuNi/Nb/CuNi films via magnetron sputtering and confirmed the theoretical prediction by measuring the resistance of the system as a function of temperature and magnetic field. We find an approximately 25% resistance drop occurs near T(c) in Cu0.47Ni0.53(5 nm)/Nb(18)/CuNi(5) when the two CuNi layers change their magnetization directions from parallel to antiparallel, whereas there is no corresponding resistance change in the normal state.     

Combined analysis of static and dynamic magnetic characteristics of multilayer CoFeZr/α-Si nanostructures

The combined method of static and dynamic magnetic measurements is used to study nano-dimensional multilayer amorphous CoFeZr/α -Si films. It is established that at the thickness of magnetic layers x = 5–12 nm their magnetization does not differ from that of the bulk material. It is shown that as x is lowered to 2–3 nm, the magnetization of magnetic layers decreases, which may be due to the formation of mixed layers containing nonmagnetic silicides. At a thickness of nonmagnetic interlayers of less than 1 nm the features characteristic of a weak antiferromagnetic interaction of neighboring layers are observed.