Effects of interfacial structure on the magnetic properties of ultrathin Fe/Pt(111) films with Ag buffer layer

For Fe/Pt(111) grown at 180 K, the easy axis of magnetization changes from out-of-plane to in-plane while the surface structure changes from fcc(111) to bcc(110). The Curie temperature for 1 ML Fe/Pt(111) is close to room temperature. After insertion of submonolayer Ag, no significant change for the Curie temperature is observed. By thermally annealing Ag/Pt(111) at 550 K to form a Ag-Pt surface alloy, we demonstrate that the Curie temperature of the deposited Fe films is elevated to be higher than room temperature. For an ultrathin Fe/Ag/Fe/Pt(111) sandwich system, the strong interaction between the two Fe layers is superior due to the effect of the double Fe/Ag interfaces. This causes that the easy axis of the magnetization switches back to the in-plane direction during the deposition of Fe overlayer on the surface of a Ag/Fe/Pt(111) film.     

Annealing behavior of magnetic anisotropy in CoNbZr films

The effect of magnetic and nonmagnetic annealing on the magnetic anisotropy in CoNbZr films, formed by a DC opposing-targets sputtering method, was investigated. It was revealed that the origin of the magnetic anisotropy is the directional ordering of the magnetic atoms. The anisotropy fields and the direction of the easy axis obtained when the films are annealed in zero magnetic field are almost the same as those for the magnetic field parallel to the easy axis of the as-deposited films. When the films are annealed in a magnetic field perpendicular to the easy axis, the anisotropy field induced in parallel with the magnetic field, H_k(t), is well represented by the following formula: ln {1-H_k(t )/H_k(∞)∝-√Tt, where H_k(∞) is the thermal equilibrium value of the anisotropy field and D is the diffusion constant. The activation energy of the as-deposited film is 0.86 eV. Annealing the film increases the activation energy which is 2.1 eV when the film is annealed at a temperature of 450°C for 2 h     

Optical and ferromagnetic characteristics of Mn doped ZnO thin films grown by filtered cathodic vacuum arc technique

Mn doped ZnO (ZnO:Mn) thin films with ~ 10 at.% of Mn were grown on quartz substrates by filtered cathodic vacuum arc (FCVA) technique at low substrate temperature (≤ 200 °C). The influence of substrate temperature and oxygen flow rate on the optical, electrical and magnetic properties of the ZnO:Mn thin films was studied. Both room temperature ferromagnetism and ultraviolet photoluminescence were observed in all films. A maximum saturation moment of 2.9 × 10⁻²⁴ A m²/Mn can be achieved for the films grown in an optimum condition. This suggests that the fabrication of high-quality ZnO:Mn films by FCVA technique has the potential to realize efficient magneto-optic devices operating at ultraviolet regime.     

Optical and magnetic properties of Mn doped ZnO thin films grown by SILAR method

Polycrystalline Mn doped ZnO (MZO) semiconductor thin films were deposited onto glass substrates employing different number of dipping at room temperature using Successive Ionic Layers by Adsorption Reaction (SILAR) technique. The thin film deposition conditions were optimized by altering the various deposition parameters based on their structure. The structural study was carried out using X-ray diffractometer (XRD). The XRD analysis indicated that there is no change in the structure of ZnO thin films due to Mn doping. The films exhibited hexagonal wurtzite structure. The structural studies on Mn doped samples revealed that the predominant orientation is (002) lattice plane and the position of this orientation shifted toward lower angle during doping. The intensity of photoluminescence (PL) emission of ZnO is found to be augmented for Mn doped samples. The room temperature Raman spectra measurements revealed the presence of additional modes. The Vibrating Sample Magnetometer (VSM) studies show that MZO thin film has ferromagnetic properties.     

Thermopower and optical studies on undoped and manganese doped indium tin oxide films

Thermopower measurements in the range of 300-650 K along with room temperature optical absorption and electrical resistivity studies have been performed on indium tin oxide (ITO) and manganese doped indium tin oxide (Mn:ITO) thin films grown by reactive DC sputtering. The thermopower of the films measured in Ar ambient displayed irreversible changes attributable to oxygen loss. Thermopower, carrier concentration and resistivity of the films have been found to depend on oxygen vacancies and Mn concentration. The observations have been substantiated with optical absorption and room temperature electrical resistivity results. It has also been observed that band gap tuning in these films is possible by the introduction of Mn as well as oxygen vacancies.     

Surface spin slips in thin dysprosium films

We report a theoretical investigation of new magnetic phases of thin dysprosium films. At the surfaces, the balance between exchange and anisotropy energies favors the alignment of spins along the basal plane easy axis directions. Near the Curie temperature, the helimagnetic phase is strongly modified, allowing surface spins to lock into the basal plane anisotropy easy directions. As the temperature raises, we find transitions to other surface lockin patterns, which are tunable by external field strengths of a few hundred milli-Oersteds.     

Relaxation of magnetoelastic phenomena in electrodeposited nickel-iron films

Cylindrical 5 μm films of Ni-8% Fe alloy electrodeposited onto a substrate wire, with the easy axis of magnetization in a circumferential direction and the hard axis coinciding with the substrate axis, can be used as sensors of tension. The change of the anisotropy field H_k is proportional to the strain produced in the film and can be observed as a change of the current in a measuring circuit. However, at constant load (and strain) a considerable relaxation occurs, which can be represented as an exponential function of time, at least for periods shorter than 10 min. The rate of relaxation is temperature dependent with an apparent activation energy of 0.3 eV. It is suggested that the observed phenomena are due to the migration of defects and to their interaction.     

Ageing and piezoresistance of island manganese films

Island manganese (Mn) films of mass thicknesses 2, 4, 6, 8 nm were deposited on Corning 7059 glass substrates at ambient temperature. The deposition took place in vacuum by the thermal evaporation technique. The dependence of the d.c. resistance of the as-deposited Mn films on time (ageing) was studied in air at a room temperature of 20 C over a period of 110 H. It was found that the increase in resistance lasts for relatively short intervals, in comparison with many other island films, before the resistance attains a stable value. The length of the time intervals decreases with increase of film thickness. The response of the stabilized Mn films to longitudinal and transverse induced strains was investigated and the corresponding gauge factors were deduced. The gauge factor increases with decrease of film thickness. The sensitivities of the present films to the two types of strain are comparable. The data of the research are discussed with the view that the quantum mechanical tunnelling model is the mechanism responsible for the electrical conduction in our films.     

Preparation and characterization of Mn-doped BaTiO<Subscript>3</Subscript> thin films by magnetron sputtering

Barium titanate (BaTiO₃) thin films doped with Mn (0.1–1.0 at%) were prepared by r.f. magnetron sputtering technique. Oxygen/argon (O₂/Ar) gas ratio is found to influence the sputtering rate of the films. The effects of Mn doping on the structural, microstructural and electrical properties of BaTiO₃ thin films are studied. Mn-doped thin films annealed at high temperatures (700 °C) exhibited cubic perovskite structure. Mn doping is found to reduce the crystallization temperature and inhibit the grain growth in barium titanate thin films. The dielectric constant increases with Mn content and the dielectric loss (tan δ) reveals a minimum value of 0.0054 for 0.5% Mn-doped BaTiO₃ films measured at 1 MHz. The leakage current density decreases with Mn doping and is 10⁻¹¹ A/cm⁻² at 6 kV/cm for 1% Mn-doped thin films.     

Influence of the Magnetic Anisotropy Dispersion in Ge3Mn5 Clusters on the Temperature Dependences of Magnetization in Thin Ge:Mn Films

Technical Physics Letters - The temperature dependences of magnetization M(T) of thin ion-implanted Ge:Mn (4 at % Mn) films containing Ge3Mn5 clusters were measured on samples cooled in the absence...     

Room temperature paramagnetism of ZnO:Mn films grown by RF-sputtering

ZnO:Mn transparent thin films (thickness < 1 μm) with the Mn contents ranging from 1.8 to 3.25 at.% were grown by RF magnetron co-sputtering. The films are nanocrystalline, with wurtzite-structure grains of a typical size of 20 nm and with a preferential orientation of the c-axis perpendicular to the surface. According to the Raman spectroscopy data, Mn mostly substitutes Zn in the lattice sites. In spite of these factors, the nanostructure and the Mn(Zn) substitution, that are considered favorable for ferromagnetism in this material, both magnetic resonance and Faraday effect measurements show paramagnetic behavior of the ZnO:Mn films and the absence of ferromagnetic order at room temperature.     

Relative stability of an on-top and an inverted Mn monolayer on Ag(1 0 0): Experiment and theory

Mn films with a thickness of one monolayer (ML) have been deposited in ultra-high vacuum, at room temperature (RT), on a Ag(1 0 0) single crystal. Photoemission and ion scattering spectroscopy data indicate that after Mn evaporation a substantial fraction of the Mn atoms is located within the second topmost atomic layer. If the film is left at RT or mildly (60 °C) annealed, the Mn atoms tend to exchange further with Ag atoms, increasing the Mn concentration in the second atomic plane. Eventually the second atomic plane of the sample is constituted mainly by Mn atoms, whereas the first atomic layer is almost a pure Ag plane, i.e. an inverted atomic Mn ML is formed. To directly compare experiment and theory, we have performed ab initio electronic band structure calculations on the energetic stability of 1 ML of Mn on top of Ag(1 0 0) versus 1 ML of Mn covered by one Ag atomic plane. The case of a 2 ML-thick MnAg alloy is also investigated. The relation between magnetism and stability of Mn films is discussed.     

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films

In this study, we report about the occurrence of phase separation through spinodal decomposition (SD) in spinel manganese ferrite (Mn ferrite) thin films grown by Dynamic Aurora pulsed laser deposition. The driving force behind this SD in Mn ferrite films is considered to be an ion-impingement-enhanced diffusion that is induced by the application of magnetic field during film growth. The phase separation to Mn-rich and Fe-rich phases in Mn ferrite films is confirmed from the Bragg’s peak splitting and the appearance of the patterned checkerboard-like domain in the surface. In the cross-sectional microstructure analysis, the distribution of Mn and Fe-signals alternately changes along the lateral (x and y) directions, while it is almost homogeneous in the z-direction. The result suggests that columnar-type phase separation occurs by the up-hill diffusion only along the in-plane directions. The propagation of a quasi-sinusoidal compositional wave in the lateral directions is confirmed from spatially resolved chemical composition analysis, which strongly demonstrates the occurrence of phase separation via SD. It is also found that the composition of Mn-rich and Fe-rich phases in phase-separated Mn ferrite thin films deposited at higher growth temperature and in situ magnetic field does not depend on the corresponding average film composition.     

Effect of dopant concentration on the structural, electrical and optical properties of Mn-doped ZnO films

The Mn-doped ZnO (Zn_1 − xMn_xO) thin films with manganese compositions in the range of 0-8 at.% were deposited by radio-frequency (RF) magnetron sputtering on quartz glass substrates at room temperature (RT). The influence of Mn concentration on the structural, electrical and optical properties of Zn_1 − xMn_xO films has been investigated. X-ray diffraction (XRD) measurements reveal that all the films are single phase and have wurtzite structure with (002) c-axis orientation. The chemical states of Mn have been identified as the divalent state of Mn²⁺ ions in ZnO lattice. As the content of Mn increases, the c-lattice constant and the optical band gap of the films increase while the crystalline quality deteriorates gradually. Hall-effect measurements reveal that all the films are n-type and the conductivity of the films has a severe degradation with Mn content. It is also found that the intensity of RT photoluminescence spectra (PL) is suppressed and saturates with Mn doping.     

溅射法制备Mn-Zn铁氧体薄膜的磁性与微结构

以交替真空溅射的方法使用成分分别为MnFe2O4与ZnFe2O4的双靶制备了成分变化的系列Mn1-xZnxFe2O4铁氧体薄膜,衬底为Si(100)。薄膜的成分通过控制不同靶的溅射时间来进行调整。沉积态的薄膜呈非晶结构,在真空炉中以适当的温度对薄膜进行退火之后能够得到多晶Mn-Zn铁氧体薄膜。组成成分为Mn0.5Zn0.5Fe2O4的薄膜呈现了相对最高的饱和磁化强度。同时还研究了制备条件对薄膜结构与磁性的影响,如溅射氧分压,退火真空度,退火温度及薄膜厚度等等。制备的薄膜相对于块状材料具有较高的矫顽力,进而讨论了应力对薄膜矫顽力的影响。     

On the origin of oblique-incidence anisotropy in evaporated cobalt films

The main results obtained when studying a temperature dependence of the uniaxial anisotropy of oblique-incidence magnetic films of cobalt are given. It has been stated that when depositing the films onto a substratum heated to 350°C, the easy magnetization axis (EA) is perpendicular to the incidence plane of a molecular beam (a positive anisotropy). EA is in the incidence plane (a negative anisotropy) when the temperature of a substratum is 60 to 80°C. At intermediate temperatures of a substratum a positive anisotropy arises at small angles of deposition and a negative one is at great angles of deposition. Temperature dependences of the constant of the uniaxial anisotropy for samples with a positive or negative anisotropy distinguish between each other. In samples with a positive anisotropy this constant changes with the temperature as a square of magnetization; in samples with a negative anisotropy at less than room temperatures, this constant is approximately proportional to the anisotropy constant of a massive-cobalt single crystal. The obtained results have been considered from the theoretical point of view, and it has been concluded that a negative anisotropy in oblique-incidence films arises as a result of formation of very small grains stretching in the direction of the incidence plane and having a significant anisotropy of the magnetic energy in layers adjoining the boundaries (the Néel anisotropy). Observation of the typical temperature dependence of the anisotropy constant of these samples is a very convincing proof of existence of the Néel anisotropy.     

热处理温度对溶胶-凝胶法制备ZnO薄膜晶体结构和发光特性的影响

采用溶胶-凝胶(Sol-Gel)旋涂法在Si(100)衬底上制备ZnO薄膜,利用X射线衍射(XRD)、光致发光谱(PL)、扫描电子显微镜(SEM)等手段分析制得的ZnO薄膜的晶体结构和发光特性。着重考察了热分解温度对ZnO薄膜晶体结构和发光特性的影响。结果表明,溶胶-凝胶旋涂法制备的ZnO薄膜样品厚度约为220nm,属六方纤锌矿结构,其c轴取向度与热分解温度有很大关系;ZnO薄膜在室温下均有较强的紫外带边发射峰,且紫外带边发射峰与样品c轴取向度没有直接关系,与缺陷有关的可见发射带很弱。     

Magnetic and dielectric properties of Yb(Mn1-xAlx)O3 thin films

Hexagonal RMnO(3) is known as one of the candidates for multiferroic materials. We have focused on YbMnO(3), which has ferroelectricity along the c axis below 1000 K and antiferromagnetic ordering below 80 K. We have reported that magnetic, field-induced ferromagnetism in YbMnO(3) epitaxial thin films. In this study, we investigate the substitutional effect of the nonmagnetic element, Al, for Mn ions with triangular spin ordering on the ferroelectric and magnetic properties of YbMnO(3).     

Effect of Exchange Bias on Magnetic Anisotropies in Fe/CoO Bilayers

We report on the structural and magnetic properties of exchange-biased Fe/CoO bilayers grown on MgO (001) substrates by using rf-sputtering. For varying Fe thicknesses (4 nm, 10 nm, and 20 nm) the ferromagnetic resonance (FMR) spectra of bilayers have been studied as a function of temperature at X-band frequency. The resonance lines of FMR spectra have a relatively small linewidth indicating a high crystallinity of the Fe films. The room-temperature FMR data also show that the easy axis of Fe is in the film plane and parallel to the [110] crystallographic direction of MgO substrate. In addition, M versus H loops were recorded at selected temperatures by using VSM magnetometry. The VSM measurements indicate that the Fe thickness and temperature dependence of exchange-bias properties are in good agreement with the previous results on similar systems. However, the blocking temperature of the exchange-biased system is strongly reduced compared to the bulk values. This reduction in the blocking temperature is explained by both the thickness and superstoichiometric structure of antiferromagnetic CoO layer.     

掺Mn硅酸锌薄膜中微量氧化锌对发光强度的影响

利用溶胶-凝胶法结合高温热处理在硅衬底上制备了掺Mn硅酸锌薄膜，用XRD、SEM、UV-Vis吸收谱和PL谱测试了样品的结晶性能与光学性能，并分析了热处理温度对掺Mn硅酸锌薄膜的结晶性能和光学性能的影响．实验结果发现，ZnO的适量存在对掺Mn薄膜的发光有增强作用．进一步的分析认为，这一现象的机理可由G．G．Qin提出的量子约束-发光中心（QCLC）模型进行解释，ZnO中受激发的电子和空穴通过隧穿效应到达硅酸锌基体中复合发光，从而增强发光强度．