Structural, magnetic, and magneto-optical properties of nanocrystalline face centered cubic Co70Cr30/Pt multilayers with perpendicular magnetic anisotropy

Co70Cr30 alloyed layers are combined with extremely thin Pt layers in order to produce novel face-centered-cubic multilayered films to be considered as a potential perpendicular magnetic recording medium. The films were grown on Si, glass and polyimide substrates by e-beam evaporation at a temperature slightly higher than room temperature. The multilayered structure of the films was verified by X-ray diffraction experiments. Plane-view transmission electron microscopy images have revealed the formation of very small grains in the range of 7-9 nm. Hysteresis loops as a function of temperature were recorded via the magneto-optic Kerr effect in the polar geometry configuration. The system exhibits perpendicular magnetic anisotropy, which enhances with decreasing temperature. Hysteresis loops with a squareness of 1 and a coercivity of 1.45 kOe were obtained at 10 K. Furthermore, complete magneto-optic spectra of the films are recorded, showing a strong magneto-optic enhancement in the ultraviolet region at around 4.5 eV.     

Engineering magnetic nanostructures with inverse hysteresis loops

Top-down lithography techniques allow the fabrication of nanostructured elements with novel spin configurations,which provide a new route to engineer and manipulate the magnetic response of sensors and electronic devices and understand the role of fundamental interactions in materials science.In this study, shallow nanostructure-pattemed thin films were designed to present inverse magnetization curves,i.e.,an anomalous magnetic mechanism characterized by a negative coercivity and negative remanence.This procedure involved a method for manipulating the spin configuration that yielded a negative coercivity after the patterning of a single material layer.Patterned NiFe thin films with trench depths between 15％-25％ of the total film thickness exhibited inverse hysteresis loops for a wide angular range of the applied field and the trench axis.A model based on two exchange-coupled subsystems accounts for the experimental results and thus predicts the conditions for the appearance of this magnetic behavior.The findings of the study not only advance our understanding of patterning effects and confined magnetic systems but also enable the local design and control of the magnetic response of thin materials with potential use in sensor engineering.     

Anisotropic behaviour of the glass transition temperature in thin films of Langmuir-Blodgett deposited side chain polymers

Langmuir-Blodgett (LB) films of side chain polyamic acids were formed, deposited onto optical waveguides and imidized via heating to the corresponding polyimides on the optical waveguides. The LB film formation of the side chain polyamic acids, the imidization reaction and the glass transition behaviour of the polyimide thin films were investigated. Polarisation dependent waveguide mode spectroscopy was applied therefore. It was found that the glass transition temperature (Tg) of bulk and LB thin film samples of these polymers are identical and only depend on the spacer length between the side chain and backbone, not on film thickness. Our investigation shows that in the case of the ultrathin film geometry, the glass transition temperature exhibits an anisotropic behaviour. We find the classical kink in the temperature scan (a change in slope of the free volume vs. temperature plot) due to the thermal expansion change at Tg, in p-polarisation only, which is perpendicular to the main chain orientation. In the s-polarisation measurements (parallel to the main chains) no kink was found, only an offset in the vicinity of Tg. We attribute the anisotropic thermal behaviour to a transition, the freezing of segmental motion, in the side chains only.     

真空退火Co/Pt多层膜的结构、磁及磁光特性分析

本文用直流磁控溅射方法制备了Co／Pt多层膜,并对其进行了较为细致的真空退火处理,结果表明,适度的低温退火可增加Co／Pt多层膜的矫顽力,而并不削弱其磁滞克尔回线的矩形特征．当退火温度达到300℃以后,Co／Pt多层膜的矫顽力、垂直各向异性和克尔角将强烈下降,晶体结构的改善及应力的释放、晶粒的增长、层间原子扩散引起的Co层有效厚度减薄,进而居里温度的下降,分别是Co／Pt多层膜在低温、中温、高温退火过程中,磁及磁光性能变化的主要机制．     

Magnetic properties and first-order magnetic phase transition in single crystal FeRh thin film

To understand the mechanism of first-order magnetic phase transition in ordered FeRh thin films, the magnetic properties and first-order antiferromagnetic (AFM)–ferromagnetic (FM) phase transition behavior of single-crystal FeRh thin film are investigated in detail. The first-order magnetic phase transition is seen at a temperature of around 120 °C during heating and 145 °C cooling processes in perpendicular direction. The M–H loops measured isothermally amidst the AFM–FM transition regime show an opening at high magnetic field, which indicate a reversible AFM–FM transition induced by magnetic field. The clusters of the FM phase nucleate in the AFM matrix heterogeneously and vice versa during the first-order phase transition and the mechanism of nucleation and growth kinetics of the first-order magnetic phase transition in ordered FeRh thin film is quite similar to that of the crystallization of solids described by the Avrami model.     

Sintering Effect of Annealed FePt Nanocrystal Films Observed by Magnetic Force Microscopy

Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500degC. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605degC-630degC. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing     

Pb O3 成分梯度铁电薄膜的结构及性能

采用Sol-Gel方法,通过快速热处理,在Pt/Ti/SiO₂/Si衬底上制备出Pb (Zr, Ti) O₃成分梯度薄膜。用俄歇微探针能谱仪 (AES) 对制备的上梯度薄膜进行了成分深度分析,证实其成分梯度的存在。XRD分析表明,制备的梯度薄膜为四方结构和三方结构的复合结构,但其晶面存在一定的结构畸变。介电温谱测试表明,随着温度的升高,梯度薄膜出现一个铁电-铁电相变点和两个居里点,同时出现一定的频率弥散现象。不同偏压下电滞回线的测试表明,梯度薄膜表现出良好的铁电性质。热释电性能测试表明,梯度薄膜的热释电系数随着温度的升高逐渐增加,并且其热释电系数比每个单元的热释电系数大。      

Control of magnetic properties in metallo-organic thin films

Magnetic metallo-organic thin films have been prepared at different growth temperatures to characterize the influence of structural properties on the magnetic characteristics. A quantitative analysis of the grain size shows that the growth temperature increases the elliptical grain size considerably. Long grains of planar iron phthalocyanine form quasi one-dimensional iron chains, which are embedded in a carbon matrix along the other two dimensions. The chains are narrowly spaced (1.3 nm) and run parallel to the substrate. Temperature-dependent magnetization curves depend on the structural details of the iron chains. These magnetic properties are tuned with deposition parameters.     

Observation of recorded magnetization patterns by electron holography

Magnetization patterns recorded on Co thin films prepared by oblique incidence vacuum deposition were directly observed by electron holography. Complicated ellipse-like interference fringes were observed along the sawtooth-like walls in the transition regions. Stray magnetic flux was observed in empty space beyond the edge of the film. The following results were obtained from analysis of these interference images. The smaller the product of the remanence and the film thickness, and the higher the coercivity, the narrower is the transition length that determines the limit of the recording density of a medium. It was confirmed that longitudinal magnetic recording of a density of up to 170 kBPI is attainable using Co film 30 nm thick and with coercivity of 112 kA/m. It was quantitatively proven that the intensity of the recorded magnetization in a medium is equal to its remanence when the magnetized area is distinguishable from the transition region.     

Structure and Magnetic Properties of La0.66Sr0.33MnO3 Thin Films Derived Using Sol-Gel Technique

In this paper the results of a study of the structural and magnetic properties of La_0.66Sr_0.33MnO₃ (LSMO) polycrystalline films grown on glass substrate using Sol-Gel technique are presented. The samples were structurally characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The average grain size range of 30 nm has been obtained from XRD investigations of granular LSMO samples. Zero Field Cooling (ZFC) and Field Cooling (FC) magnetization measurements have been performed and magnetic hysteresis loops of LSMO were recorded at various temperatures. The temperature dependences of the magnetization of LSMO films recorded in ZFC and FC regimes exhibited considerable difference between the curves. The blocking and the ferromagnetic phase transition temperatures of about 262?K and 300?K, respectively, were observed from magnetization measurements.     

Electroless deposition of CoPtWP magnetic thin films

CoPtWP magnetic thin films were prepared by electroless deposition. The influence of bath pH, deposition temperature and bath composition on the deposition speed, alloy content, microstructure, and magnetic properties of CoPtWP thin films were investigated. It was found that deposition speed increased gradually with the bath pH and deposition temperature. The cobalt content in the CoPtWP thin films varied from 77 at.% to 85 at.% by controlling the bath pH. The microstructure of CoPtWP thin films was dependent on bath pH and deposition temperature: two mixed structures, face centered cubic (fcc) and hexagonal close packed (hcp), were observed at low pH values and low deposition temperature. With the increase of pH values and deposition temperature, the intensity of fcc (111) peak suppressed gradually. The surface morphology was markedly influenced by bath pH, deposition temperature and bath composition. VSM and MFM measurements revealed that perpendicular coercivity had been increased with the bath pH. Unique hard magnetic properties of CoPtWP thin films with large perpendicular magnetic anisotropy were obtained at 90 °C and bath pH 13.0.     

Crystallographic structure and magnetic properties in L1(0) FePt thin films deposited at different temperature

The crystallographic structure and magnetic properties of L1(0) FePt thin films deposited at different substrate temperature were investigated systematically in present paper. The ordered L1(0) FePt thin film was developed when substrate temperature is higher than 300 degrees C. The ordering parameter S, the degree of tetragonality c/a, and the epitaxial quality of the films, increase with increasing substrate temperature. The squareness and coercivity in the direction perpendicular to the film increase as the substrate temperature is increased and the perpendicular anisotropy is developed when the substrate temperature is higher than 300 degrees C. The magnetic anisotropy Ku increases with increasing substrate temperature and it might be concluded that the magnetic anisotropy of ordered L1(0) FePt thin films mainly stems from the magnetocrystalline origin and also possibly due to pair ordering mechanism.     

High coercivity in nanostructured Co-ferrite thin films

Three methods including sol-gel, rf sputtering and pulsed laser deposition (PLD) have been used for the fabrication of high coercivity Co-ferrite thin films with a nanocrystalline structure. The PLD method is demonstrated to be a possible tool to achieve Co-ferrite films with high coercivity and small grain size at low deposition temperature. High coercivity, over 10 kOe, has been successfully achieved in Co-ferrite films with a thickness of ∼ 100 nm deposited using PLD with a substrate temperature at 550°C. The Co-ferrite films prepared by PLD at over 300°C on different substrates including amorphous glass, quartz and silicon exhibits an obvious (111) textured structure and possesses perpendicular anisotropy. Our study has also shown that the high coercivity is related with a large residual strain, which may induce an additional magnetic anisotropy (stress anisotropy) and at the same time serve as pinning centres, which can restrict the domain wall movement and therefore, increase the coercivity.     

Magnetic Field Effects on Surface Morphology and Magnetic Properties of Co–Ni–N Thin Films Prepared by Electrodeposition

The surface morphology and magnetic properties of Co?CNi?CN thin films electrodeposited under an external magnetic field were investigated. The films were electroplated on Al substrates using the same electrodeposition parameters (temperature and pH) for all experiments, with an external magnetic field of 107?Oe applied to the cathode surface. The films were compared with similar samples obtained in the absences of magnetic field. The magneto-induced modifications in the Co?CNi?CN morphology can be explained by the specific local convection of ions at the interface cathode-electrolyte, which promotes changes both in the electrical charge of the double layer and in the thickness of the diffusion layer. From the magnetic measurements, we found that the coercivity varied between H _c =(14÷27)?kA/m depending on the direction of the applied magnetic field and on the sodium nitrate content in the plating bath. It was observed that an induced anisotropy appeared in the Co?CNi?CN films due to the preferential orientation of the easy axis of magnetization in the magnetic field direction. In addition, the Co?CNi?CN alloy films showed good magnetic property, which is considered that not only the smaller grain size of the films, but also more uniform surface of the films than that deposited in absence of applied magnetic field.     

Aging effect on coercivity of iron oxide thin films

Changes in magnetic properties for Fe_3-x□_x O₄ (x: oxidation degree) thin films made by reactive sputtering and subsequent heat treatments have been examined under room temperature aging and constant temperature annealing. Aging causes variations in coercivity of insufficiently oxidized films which have a specific resistance of less than 1×10¹ Ω·cm, while the coercivity of γ-Fe₂O₃ (x=1/3) did not change. This phenomenon did not depend on additive elements or preparation method. Other magnetic properties such as saturation magnetization, residual magnetization, squareness ratio and coercive squareness, were not affected by aging for any Fe_3-x □_xO₄ composition. The activation energy for a coercivity change is 0.72-0.95 eV near room temperature for films with a specific resistance below 1×10¹ Ω·cm. It was confirmed that only the coercivity varied at 20°C, while both coercivity and the degree of oxidation changed with annealing at 100°C     

退火温度对NiZn铁氧体薄膜性能的影响

采用射频磁控溅射法在Si(100)基片上制备了NiZn铁氧体薄膜,研究了退火温度对薄膜性能的影响.采用XRD分析仪分析了薄膜的相结构,原子力显微镜分析了薄膜的表面形貌,振动样品磁强计测量了薄膜的磁性能,结果表明,随着退火温度的升高,薄膜的结晶状态越好,晶粒尺寸越大,饱和磁感应强度越高,面内矫顽力越小.     

The effect of stress on the magnetic properties of sol–gel-derived Pr0.9Ca0.1MnO3 thin films

The Pr_0.9Ca_0.1MnO₃ (PCMO) thin films prepared by sol–gel method suffered tensile and compressive stress grown on SrTiO₃ and LaAlO₃ substrates. The hysteresis loops at different temperatures show that the coercivity field with tensile stress is larger and the pinning potential of ferromagnetism motion is much stronger. The temperature dependence of the ZFC and FC magnetizations indicates that the stress significantly affects the ferromagnetic (FM) and antiferromagnetic transition temperature of PCMO, and the Curie temperature (T_C) decreases with tensile stress. The films show strong anisotropy properties that the magnetization increases much faster with the magnetic field when H⊥c, but the coercive field and saturation magnetization do not change significantly. In addition, the persistent photoinduced magnetization is investigated, and significant improvement of the FM ordering was observed in low temperature. And the saturation magnetization of each Mn ion is significantly affected by orientation and illumination.

     

Effects of surface topography on magnetization reversal of magnetic thin films

The influence of the created surface roughness on the coercivity of magnetic thin films has been investigated. The magnetic thin films (CoFe and alternatively NiFe) are sputtered on top of smooth substrates that were previously covered with an array of considerably rougher lines with one of these materials Pt, Cu, CoFe, and NiFe. The lines have been patterned using optical lithography into arrays that are deposited with different thicknesses varying between 5 nm-15 nm. The lines have been designed to have a very rough edge and seated in two different angles relative to the wafer edge (zero and 45 degrees). Magneto-optic Kerr effect (MOKE) measurements showed two distinct switching fields in the hysteresis loops that are due to magnetic domain wall trapping created by the surface roughness. The magnetization reversal showed a strong dependence on the height, the orientation angle, and the material's type of the created surface roughness (the lines).     

The behaviour of the galvanomagnetic properties of thin films of nickel deposited on liquid-helium-cooled sapphire substrates

We report measurements of the temperature variation of the Hall effect, magnetoresistance and resistivity of thin films of nickel deposited onto optically flat sapphire substrates at 4 K. The as-deposited films showed almost square hysteresis loops for the Hall voltage as a function of the applied field. The loops disappeared as the films were annealed to 500 K, the Hall voltage reverting to the normal shape expected for a thin ferromagnetic film orthogonal to an external magnetic field. The annealed films 4–20 nm thick gave magnetization values at high temperatures that were close to those expected for bulk nickel.     

Dependence of coercivity on driving field in multilayer films of nickel

The variation in the coercivity of magnetization loops of multilayer films of nickel was investigated as function of the rate of riserin the applied magnetic field. The films were prepared by deposition of nickel and copper alternately in a vacuum of2 times 10^{-6}mm of Hg on to substrates made of thin aluminium foils. The thickness of the nickel layersLvaried in the different films from 8 to 1000 angstroms. The loops were cycled with sinusoidal or triangular waveform driving fields, with a variety of amplitudes from 1 kOe to 4 kOe, with frequencies from 0.01 to 2 c/s. The measurements were performed from room down to liquid hydrogen temperatures. It was found that the coercive force could be expressed byH_{c} = H_{o} + Q(ln r - ln r_{o})/T^{1/2}for values ofrchanging from 1 to 5 Oe/ms, whereH_{o}, Aand rovaried slightly with temperatureT. The coercive force was a very sensitive function ofLand of the thickness δ of the copper layers, having the formH_{c} = A(L + delta) exp - BLwithBnearly constant in films deposited on a substrate at room temperature. The dependence of the coercivity onLwas displayed by a nonmonotonical function showing two peaks in Hccorresponding to values ofLof about 35 and 400 angstroms. The observed dependence of Hcon the rate of rise in the applied field, as well as on the thicknesses of the layers, can be discussed on the assumption of nonuniform magnetization within the thin layers as a result of their superparamagnetic properties and of the magneto-statical coupling between neighboring layers.