Magnetism in Nanoislands: a Monte Carlo Study

The properties of nanoislands consisting of mixed spins-2 and -5/2 have been investigated using Monte Carlo simulations. Some interesting phenomena have been found in the thermal variations of the nanoisland system. The shapes of total magnetization and total magnetic susceptibility are greatly influenced by the exchange couplings. The reduced transition temperature of the nanoisland is deduced. The magnetic hysteresis cycles are obtained for different temperatures, crystal fields, and exchange interactions. Some results obtained in the nanoisland may have potential applications in different research fields, such as electronics, optics, mechanics, and even biomedicine and molecular devices.     

Effects of Biaxial Crystal Field on the Magnetic Properties on?a?Spin-1?Ising?System

Within the effective field theory (EFT) with a probability distribution technique that accounts for the self spin correlation functions, the magnetic properties such as the hysteresis loops, susceptibility and magnetization of a spin-1 Ising system with effects of a biaxial crystal field are studied. The effects of the biaxial crystal field on the magnetic properties are discussed and numerical calculations are performed and analyzed for the cases of the honeycomb lattice. A number of interesting phenomena such as the shape of the hysteresis loops and the susceptibility have been found.     

Integrated On-line Instrumentation System of Magnetic Properties Measurement

1. IntroductionA magnetic inspect system has been developed formeasuremellt of the magnetic properties of soft magnetic materials. Measurements are all made underon-line computer control using a standard IBM notebook computer. The magnetic field is controlled usingan analog output line from the control and data acquisition system, which operates a bipolar power supply.The properties measured by the system are all struture sensitive and consequently the system has beenused in the nondestructi…     

The Magnetic Properties of the Spin-1 Ising System with?the?Effect of the Transverse Crystal Field

Within the framework of the effective-field theory with a probability distribution technique which accounts for the self-spin correlations, we study the magnetic properties of the spin-1 Ising system with the transverse crystal field and the applied external magnetic field. The influence of the transverse crystal field on the phase diagrams, hysteresis loops and susceptibility is discussed in detail.     

Structures and magnetic properties of ZnO nanoislands

Using first-principles calculations, we systematically study the atomic structures and electronic properties for two dimensional triangular ZnO nanoislands that are graphite-like with monolayer and bilayer thickness. We find that the monolayer ZnO nanoisland with oxygen-terminated zigzag-edges is magnetic at its ground state, and the magnetism comes from the oxygen-edge states. The other monolayer and bilayer ZnO nanoislands with different edge structures are all nonmagnetic at their ground states. It is further revealed that for different ZnO nanoislands, their magnetic properties are quite dependent on their sizes, with larger nanoislands having larger magnetic moments.     

Magnetooptics of single and microresonator iron-garnet films at low temperatures

We have investigated the low-temperature behavior of the optical and magneto-optical properties of (Bi, Gd, Al)-substituted yttrium iron-garnet films that are either single or microresonator, i.e. sandwiched between two dielectric Bragg mirrors. It was shown that the magneto-optical properties of the microresonators with a magnetic film core are mainly determined by the properties of the constituent magnetic films. Special attention was paid to the compositions possessing magnetic compensation temperatures. The phenomenon of the temperature hysteresis was found and discussed for several samples. This testifies the fact that the magnetic moment reorientation in a magnetic field occurs by the full cycle of the first-order phase transitions “collinear phase – non-collinear phase – collinear phase”. The Faraday hysteresis curves at around magnetic compensation temperatures are demonstrated to be very informative concerning composition of a sample. In particular, the hysteresis curves measured for the magnetic films on the garnet substrates showed bursts that indicates formation of a transition layer.     

Hysteresis properties of sintered Sm Co5permanent magnets

The magnetic properties of individual SmCo5particles have been extensively studied in the literature. In the present work, initial magnetization curves and hysteresis loops of sintered SmCo5magnets have been drawn with a hysteresigraph. The observed properties depend on the previous magnetic treatment of the sample. After thermal demagnetization, the initial susceptibility is very high; after dc field demagnetization, it is very weak. The inner hysteresis loops are often unsymmetrical. Results are interpreted by considering the magnets as particle assemblies related together by dipolar interactions.     

Hysteresis Properties of Magnetic/Non-Magnetic (M/NM) Multilayers: Monte Carlo Investigation

In this work, Monte Carlo simulation was used to model the dynamic hysteresis behavior of magnetic/non-magnetic multilayers in the framework of Heisenberg model using the spin-flip algorithm. The purpose is to investigate the hysteresis properties while varying the direction of external applied magnetic field and temperature taking account interface composition of magnetic/non-magnetic atoms. From the results, with thermal variation and interface composition, the simulated hysteresis loops change significantly due to the competition between magnetic anisotropy in magnetic films and the presence of isolated clusters at the interface.     

Orientational Dynamics and Energy Dissipation in a Liquid Dispersion of Single-Domain Ferroparticles on Exposure to a Linearly Polarized Field

A theoretical investigation of the nonlinear orientational dynamics and energy dissipation in a suspension of noninteracting single-domain ferroparticles with a magnetic hysteresis on exposure to a linearly polarized magnetic field has been performed. The bifurcation properties of the system have been studied; the amplitude and frequency dependences of the powers of total and viscous dissipation have been obtained.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 2, pp. 83–92, March–April, 2005.     

Asymmetric hysteresis loops of systems of bistable nanoscopic wires

A system of bistable magnetic nanowires of diameter D = 57 nm, length L = 115 nm, magnetization M = 370 emu/cm3 is simulated. The probability distribution of the switching fields of the wires is Gaussian, with mean Hs = 710 Oe and standard deviation u(Hs) = 105 Oe. The wires are randomly distributed on a plane, with directions parallel (OX) or perpendicular (OY) to the axis direction where the magnetic field is applied. The magnetostatic interaction between the wires leads to an asymmetry of the hysteresis loop of the system. Namely, we obtain different curves M(H) for ascending and descending magnetic field. This behaviour is due to the wires which are perpendicular to the applied magnetic field. The directions of their magnetic moments remain often unchanged during the hysteresis experiment, and their contribution to the magnetic moment measured along OX is equal to zero. However, they interact with the wires parallel to the field, and this interaction influences the magnetic state of the parallel wires. The effect can be useful when we are interested in tailoring the shape of the hysteresis loop. Also, a given magnetic configuration of the wires parallel to OY produces a unique asymmetry of the hysteresis loop of the wires parallel to OX. Once an additional field is applied along OY, this unique state is destroyed. The effect can be useful for safety systems.     

APPLICATION OF THE VILLARI EFFECT IN A FATIGUE EXAMINATION OF NICKEL

This paper presents the possibility of using the reverse magnetostriction (Villari) effect in fatigue testing of ferromagnetic materials. The tests were conducted on cyclically loaded nickel with no auxiliary external magnetic field. The following properties were determined: magnetic induction B, magnetic field strength H, energy of the magnetic hysteresis loop ΔM (in the B–H coordinate system), plus such mechanical quantities as stress σ, strain ?, plastic strain ?_p and energy of the mechanical hysteresis loop ΔW (in the σ–? coordinate system). A variety of magneto-mechanical characteristics are presented and their susceptibility to loading parameters of the fatigue process are discussed. A relationship between ΔW and ΔM is demonstrated. The Villari effect is shown to be especially useful in determining the cyclic yield limit.     

The effect of elastic stresses on super-high-frequency magnetic impedance of amorphous magnetic microwires

It has been demonstrated experimentally that, in magnetic microwires with a negative sign of the magnetostrictive constant, imposing an axial stress results in an increase of the effective field of circular anisotropy. Torsion stresses form a helical magnetic structure that yields hysteresis and irreversible jumps on giant magnetic impedance curves. The field at which the stability of a magnetic system deteriorates depends on the values of axial and torsion stresses.     

Magnetic coupling phenomena in EuS/Pb thin film double layers

The magnetic properties of EuS/Pb double layers (a ferromagnetic insulator on a superconducting metal) were investigated by means of 50 Hz hysteresis. The magnetic coupling between the two layers does not set in spontaneously. Two procedures for achieving magnetic coupling are described: first, by means of a d.c. magnetic field perpendicular to the film plane; secondly, with an a.c. field in the film plane. The coupled states are characterized by a slowing of the 50 Hz magnetization reversals. The degree of slow-down depends on the strength of the magnetic coupling.     

Local Non-contact Evaluation of the ac Magnetic Hysteresis Parameters of Electrical Steels by the Barkhausen Noise Technique

The potential of the magnetic Barkhausen noise method for local repeatable testing of the magnetic hysteresis properties of electrical steels was investigated. Strips of non-oriented and grain-oriented electrical steels were magnetized by a single yoke through 0–10 mm air gaps. The measurements were performed at standard ac conditions: 50 Hz sine induction waveform with different amplitudes. A vertically mounted array of three Hall sensors was used for the direct measurement of the surface magnetic field. The Barkhausen noise was detected locally by a surface-mounted pancake coil. The simultaneous measurement of the actual sample field makes it possible to stabilize a recently introduced parameter, called Barkhausen noise coercivity. This parameter demonstrates strong linear correlations to the hysteresis coercive force and to the hysteresis losses measured by the standard single sheet tester.     

Double Hard Axes of Hysteresis Loop in Wide-Angle Obliquely Sputtered CoFeB Amorphous Films

Soft magnetic Co₄₀Fe₄₀B₂₀ films with different tilt angle were successfully deposited on silicon substrates by using oblique sputtering technique. Different oblique angles are achieved by controlling the position of samples. The corresponding static magnetic properties of these samples were then systematically investigated. Interestingly, with the oblique angle increasing from 38° to 55°, the MOKE hysteresis loop of the thin films displays a unique and special performance with double hard axes. Meanwhile, despite of the measurement magnetic field along PR or AR direction, both of the hysteresis loops have two-stage magnetization reversal that means there are two comparably strong anisotropies in the CoFeB films. Moreover, rotating samples from in-plane to out-of-plane, the hysteresis loops demonstrate the perpendicular anisotropy exist in CoFeB films. The cross-section SEM characterizations further verify that the residual field from the magnetic cylinder will strongly impact the microstructures of thin film.     

Electrochemical,optical, and magnetic properties of Ni x InSe (0 < x ≤ 1) intercalation compounds

We have studied the electrochemical, optical, and magnetic properties of nickel-intercalated InSe single crystals. The energy position of the excitonic maximum and the full width at half maximum of the excitonic band in the Ni _x InSe intercalation compounds have been shown to be nonmonotonic functions of nickel concentration. Nickel-intercalated InSe possesses ferromagnetic properties: the dependence of its magnetic moment on magnetic field has the form of a hysteresis loop, characteristic of hard-magnetic ferromagnets.     

A New Approach for Finite-Element Modeling of Hysteresis and Dynamic Effects

Macroscopic behavior of ferromagnetic materials can be considered as the resultant of three phenomena: hysteresis, eddy current, and excess loss. Hysteresis is the behavior of the material under quasi-static variation of magnetic field. Eddy-current and excess losses are dependent on the rate of field variation and are evident in the fast variation of the magnetic field, so they are called dynamic effects. This paper presents a simple and practical technique in field analysis of electromagnetic systems having hysteresis and dynamic effects. Based on the Preisach model for hysteresis and existing formulations for eddy currents and excess loss, an equivalent expression for field intensity has been introduced. A new technique has been presented in order to include this expression in the finite-element code. A typical system has been modeled by this code. Effects of relaxation and time step were examined on the stability and the convergence rate of the method. The validity of the proposed model has been checked by comparing its results with experimental measurements     

磁导率对偏转系统的影响分析

应用EMAS(Electronic MagneticFieldAnalysisSystem)和DUEMAS软件对偏转磁芯材料的磁导率对偏转系统的影响进行了计算分析。计算结果表明 ,当磁性材料的相对磁导率大于 30 0时 ,磁导率对偏转电流的影响小于 0 6 % ,对磁滞损耗的影响小于 1% ,因此在磁性材料的选择中不必过分要求高的磁导率 ,而应在降低磁滞损耗上努力。     

振动系统中磁流变流体阻尼模型的研究

研究了磁流体的阻尼力特性,提出了基于粘性阻尼和回滞阻尼组成的迟滞阻尼力模型,进行了磁流变阻尼器阻尼力的响应谱分析,并用Newmark数值积分方法分析了带有磁流变流体阻尼器梁结构的多自由度振动系统在不同磁场强度和激励频率作用下的位移响应.结果表明:迟滞阻尼力模型能够很好地描述磁流体阻尼器的力学性能,而且形式简单,概念明确,适合实际应用.     

Modification of magnetic properties of metal nanoparticles using nanotemplate approach

We demonstrate a nanotemplate approach by which different metal magnetic nanoparticles (Ni–Co, Ni–Fe and Co–Pt alloy particles) can be fabricated on a polyimide (PI) film. The process relies on the high interfacial energy between deposited metal and the PI film which forces the deposited metal film to preferentially nucleate on the pre-existing Ni seed particles. During subsequent thermal annealing, the deposited metal film coalesced onto the Ni seed particles to form a monolayer of magnetic nanoparticles on the PI film. Furthermore, the deposition/annealing can be repeated to change both size and constituent of the nanoparticles by introducing a different metal film during deposition. Potentially, any metal film can be deposited onto the Ni seed particles provided that the metal does not react with the Ni seed particles to create a monolayer of metal nanoisland structures with desire magnetic properties.