Pulse switching in thin magnetic films

The main results of the investigations of pulse switching in thin magnetic films with uniaxial anisotropy which have been obtained in Moscow State University are reviewed. Simultaneous investigation of integral switching properties, inner effective field, and dynamic domains produced during pulse switching has increased our understanding of bi-directional incoherent rotation mechanism and found new peculiarities of the pulse switching by domain boundary propagation. A new variety of incoherent rotation which manifests itself at strong fields has been found. It has been also found that the curve representing the pulse field dependence of an inverse switching time in the general case consists of five distinct regions. The relation between these regions and the switching mechanisms are discussed.     

Monte Carlo study of thin magnetic Ising films

The average magnetization of thin simple cubic Ising films (with thicknesses n of 1, 2, 3, 5, 10 and 20 atomic layers, respectively) is calculated as a function of temperature using the Monte Carlo technique. The “magnetization profile” across the film is also obtained. To approximate the infinite extension in the plane parallel to the surfaces of the films, films with linear dimensions 55 × 55 and periodic boundary conditions are considered. The shift of the critical temperature is consistent with an n^-λ law where λ = 1/v₃ = 1.56 is the reciprocal exponent of the correlation length. This result is critically compared with previous estimates obtained by various authors using other techniques. By interpreting the results in terms of Fisher and Barber's scaling theory, the finite size scaling function for the magnetization is determined. It is pointed out that the spatial distribution of the magnetization can be reasonably interpreted in terms of surface properties.     

Astroid plotter for thin magnetic films

The rotational astroid of uniaxial thin films may be obtained from the cross-field loopm_{x} , h_{y}graphically or electronically by assuming Slenczewski's tangent rule. The graphical construction by means of the tangent rule is demonstrated. The derivation of the transformation to obtain the astroid electronically is given, and a comparison is made with astroids obtained graphically as well as those obtained by direct static measurements. An astroid plotter has been constructed using standard analog computer components in conjunction with a Kerr apparatus. The resulting displays give the entire rotational astroid and completely avoid wall switching and blocking phenomena. Examples are shown of applications of the astroid plotter with particular emphasis on obtaining the influence of bit geometry for all orientations of magnetization.     

化学镀Co-P薄膜的磁性及研究

采用化学镀法制备了Co-P磁记录薄膜.当薄膜厚度为0.3μm时,矫顽力可达4.54×104A/m,剩余磁化强度为0.068T.X射线衍射分析表明,当Co-P薄膜较薄时,薄膜结构中无明显择优取向,晶粒较小,此时矫顽力较高;当厚度增加至3～4μm以上时,结构中择优取向明显,晶粒较大,此时薄膜的矫顽力较低.将其应用于磁旋转编码器的磁鼓记录介质,制成直径φ40mm的磁鼓,当原始充磁磁极对数为512时,脉冲计数完整,输出信号强,波形稳定.     

Radiofrequency sputter deposition of germanium-selenide thin films for resistive switching

The superionic conducting properties of Ag-doped GeSe thin films make this material a promising candidate for future, resistively switching-based memories allowing for high integration densities and short switching times. This paper reports on the radiofrequency sputter deposition of GeSe thin films and on the properties of the deposited thin films with respect to non-volatile memory applications. As sputter deposition is a widely used deposition method for industrial applications, we focused on the influences of deposition parameters as power and pressure to examine the suitability of sputter deposition for fabricating random access memories using GeSe-based resistive memory cells. Multiple characterization methods were utilized to determine the quality of the deposited thin films. The results of our measurements showed that we obtained smooth, dense and amorphous layers, which reveal good switching properties after doping with Ag, suitable for the use in GeSe-based memories.     

Domain theory model for magnetic thin films

A domain-theoretic model for external-field-driven magnetization processes in thin-film microelements is described. The film is mathematically described by a dynamic grid of quadrilateral domains whose magnetization directions and vertex locations are variables with which to minimize the total free energy. The magnetostatic interaction between uniformly (in-plane) magnetized polygonal domains is essentially treated exactly. Predicted results for reversal mechanisms and field-induced metastable remanent domain configurations in Permalloy microelements are in good qualitative agreement with Bitter pattern observations     

A method for measurement of "Creep" in thin magnetic films

The "creep" phenomenon in thin magnetic films is measured using a field consisting of a static field parallel to the film's easy axis, and a high-frequency sinusoidal field along the transverse axis. A special field-gradient coil is used to establish a two-domain magnetization configuration in the film plane, and the Kerr magneto-optic effect is employed to measure the position of the disturbed domain wall. Measurements on Ni-Fe-Co and NiFe alloy films show the typically sharp threshold field below which there is no wall creep; nonuniform creep gives evidence for wall "pinning" phenomena. With the method described for field calibration and the simple form of fields employed, this procedure should be valuable in establishing comparative creep sensitivity data for films formed from different alloys or by different technologies.     

Electrical and switching properties of InSe amorphous thin films

In this work electrical and switching properties of InSe thin films have been studied.

The semiconductor compound InSe was obtained by direct synthesis from stoichiometric amounts of spectroscopically pure indium and selenium. By slow cooling of the synthesized InSe a polycrystalline material is obtained. The amorphous films were obtained by thermal evaporation under vacuum of the polycrystalline material on glass or pyrographite substrates.

From electrical measurements, it was found that for all films the dark electrical resistivity decreases with an increase in film thickness and temperature. The InSe compound exhibits non-linear I–V characteristics and switching phenomena. The threshold voltage decreases with increasing annealing temperature and increases with increasing film thickness.     

Memory switching of ZnGa2Te4 thin films

Electrical and switching property of amorphous defect chalcopyrite ZnGa₂Te₄ thin films prepared by thermal evaporation technique has been studied. The elemental chemical compositions of the prepared bulk as well as the as-deposited film were determined by means of energy dispersive X-ray spectrometry. X-ray diffraction pattern revealed that the powder compound is polycrystalline and the as-deposited and the annealed films at t _a ≤ 548 K have the amorphous phase, while that the annealed at t ≥ 573 K are polycrystalline with a single phase of a defect chalcopyrite structure similar to that of the synthesized material. The great advantage of this material is the capability to appear in two different phases, the amorphous and the crystalline phases, with rather different electrical properties. Both dynamic and static I–V characteristics and the switching phenomenon at 601 nm are investigated. The threshold switching mechanism was explained by a thermal model of switching, i.e., joule heating with an electrically conducting channel. ZnGa₂Te₄ is good candidate in phase change memory device.     

Charged walls in thin magnetic films

Charged walls are domain walls which carry a net "magnetic charge" (div M) due to their orientation relative to the domain magnetizations. They differ from ordinary Bloch and Néel walls (which are uncharged) primarily in their much wider profile. In order to calculate such walls, a variational method was developed. It is based on the separation of that part of stray field energy which would be present even with an infinitely thin wall. The main results of the calculations are as follows. 1) Isolated charged walls do exist if exchange energy is taken into account, as opposed to the periodic solution known for the limit of negligible exchange energy. 2) Rotated, partially charged walls develop a Néel-wall-like narrow core region. Detailed results for the wall profiles, energies and widths as a function of wall angle, orientation, film thickness, and material parameters are presented. They are applied to two examples: the case of a Permalloy film in a domain tip propagation memory, and the case of the implanted layer on a contiguous disk bubble device.     

Hard magnetic two-phase Co-Cu thin films

The magnetic properties of sputtered films of 25 Co-75 Cu and 50 Co-50 Cu before and after annealing were investigated. In the as-sputtered state the films exhibit the structure of a metastable fcc solid solution. Annealing at 500 to 700°C causes decomposition into two phases, Cu and fcc 89 Co-11 Cu. The decomposition supposedly occurs by heterogeneous nucleation at the grain boundaries, and growth by grain boundary diffusion. The 89 Co-11 Cu phase exists in the form of small particles with magnetic single domain behavior. The films have coercivities up to 280 Oe. Squareness ratios between 0.7 and 0.9 were found. No strain sensitivity of the magnetic properties could be detected. This material is regarded to be suitable for magnetic recording.     

CoNbZr非晶软磁薄膜晶化动力学研究

采用 DSC热分析技术,结合 XRD、TEM和AFM实验,对磁控溅射制备的 Co85.5Nb8.9Zr5.6非晶合金软磁薄膜进行了变温和等温晶化动力学的研究。研究结果表明:升温晶化时,薄膜的晶化的表观激活能为99.82kJ/mol;局域激活能随晶化度增加;在等温晶化过程中,平均激活能为 88. 51kJ/mol, Avrami 指数1.17~1.39, 晶化行为主要是一维表面晶化,晶核长大受扩散控制的过程。     

Nanoscale domain switching behaviour in polycrystalline ferroelectric thin films

We report on the nanoscale domain switching behaviour in polycrystalline tetragonal perovskite lead zirconate titanate (PZT) ferroelectric thin films investigated via piezoresponse force microscopy (PFM). Local domain structures were imaged as a function of varying biasing conditions and spatial location of the tip within 50-100?nm sized grains. Nanoscale piezoresponse images provided direct visual evidence of the complex interplay between electrical and mechanical fields in a polycrystalline system, which causes effects such as correlated switching between the grain of interest and neighbouring grains, ferroelastic domain switching, inhomogeneous piezostrain profiles and domain pinning on very minute length scales. Detailed investigations on mechanisms which induce such domain behaviour are presented.     

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.     

Oblique-field annealing effect for in-plane magnetic anisotropy ofsoft magnetic Co-Nb-Zr thin films

The effect of annealing in a magnetic field applied obliquely to the surface of soft magnetic thin films has been investigated. This annealing method was found to be extremely effective to control in-plane magnetic anisotropy without a change of annealing temperature and to suppress local anisotropy dispersion. For sputtered amorphous Co_85.5Nb_8.9Zr_5.6 thin films, it has been found that the in-plane uniaxial anisotropy energy was varied from 250 J/m³ to near zero with the coercive force H_c less than 6.5 A/m by changing the oblique-field annealing angle α. Experimental values of in-plane anisotropy energy agreed well with calculated ones predicted from α and intrinsic anisotropy induced by quasi-directional ordering. These films showed good high frequency characteristics for applying to miniaturized inductive devices