Dynamical behavior of coupled magnetic bilayers

We obtain the magnetic susceptibility of systems constituted of two coupled magnetic layers. We consider that the coupling of the films is well described by a Heisenberg like interaction to write the equation of motion for the magnetization of each part of the system. The dynamical response of each constituent material is calculated taking into account the presence of an interacting magnetic media (a magnetic layer) in its border. The susceptibility obtained incorporates the effects of a different magnetic film in the neighborhood (via the interfilm interaction), as well as the properties of the interface. We use a procedure similar to the effective medium approach developed for superlattices to obtain an effective magnetic permeability for the whole system. We show that the knowledge of this property allows one to have information on the interface of the magnetic bilayer through the analysis of its optical properties. We illustrate this point by calculating the dispersion relation of magnetic polaritons propagating in a system consisting of an antiferromagnetic (MnF₂) layer grown in direct contact with a ferromagnetic film (Fe). We also simulate numerically an optical experiment where ATR (Attenuated Total Reflection) spectra are obtained.     

外场作用下铁电/铁磁双层膜的极化磁化性质

建立了铁电/铁磁双层膜模型,铁电层的电矩用连续标量描述,而铁磁层的自旋应用经典矢量描述.利用蒙特卡罗方法模拟了体系的热力学性质和极化、磁化行为.给出了零场下体系的内能、比热、极化和磁化随温度变化的关系,并分别研究了体系在外磁场和外电场下的极化和磁化行为.模拟结果表明,双层膜体系的内能、比热、极化和磁化性质因层间耦合系数的不同而明显不同,当界面耦合较弱时,双层膜表现出各自的热力学性质,当层间耦合增强到一定程度时,双层膜耦合为一个整体,表现出统一的热力学性质.该双层膜在外场中形成电滞回线和磁滞回线,并表现出偏置特性,界面耦合强度和温度影响滞后回线和偏置现象.     

Spin Wave Spectra in a Ferromagnetic/Non-magnetic Superlatt ice with Antiparallel Magnetization

The transfer-matrix method is employed to investigate the spin waves in a ferromagnetic/non-magnetic superlat tice with an antiferromagnetic coupling between interfacial ferromagnetic layers across a non-magnetic spacer layers and the an tiparaUel magnetizations between neighboring ferromagnetic films. The dispersion relation of the spin waves is obtained. The effects of the thickness of the magnetic layers, the antiferromagnetic coupling strength and concentration of magnetic atoms at the interface on the spin wave spectra are discussed in detail.     

2-2型磁电复合薄膜CoFe2O4/Pb(Zr0.53Ti0.47)O3静磁耦合

运用溶胶-凝胶法在Pt/Ti/SiO₂/Si基片上旋涂制备了2-2型CoFe₂O₄/Pb(Zr_0.53Ti_0.47)O₃磁电复合薄膜．制备的磁电薄膜结构为基片/PZT/CFO/PZT*/CFO/PZT,通过改变中间层PZT*溶胶的浓度,改变磁性层间距以及静磁耦合的大小．SEM结果表明,复合薄膜结构致密,呈现出界面清晰平整的多层结构．制备的复合薄膜具有较好的铁电与铁磁性能．实验还研究了静磁耦合对薄膜磁电性能的影响,结果表明,随着复合薄膜磁性层间距的减小,静磁耦合效应的增加,磁电电压系数有逐渐增大的趋势.     

Production of single-crystal laminated ferro-ferrite films and certain of their magnetic properties

A method is developed for producing single-crystal magnetic laminated films of ferrite-ferromagnetic composition based on chemical transport reactions. Certain magnetic properties of these films are investigated. It is established that the exchange interaction between the ferrite film and the ferromagnetic layer depends essentially on the thickness of the diffusion layer of the latter into the ferrite layer. This leads to almost simultaneous remagnetization of both films. It is postulated that the process of rotation of the magnetic moment in the direction of the external field begins in the ferrite film and passes smoothly first into the diffusion layer and then into the ferromagnetic film. Exchange coupling considerably decreases the coercive force of ferromagnetic layers grown on ferrite films.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 90–94, May, 1974.     

Magnetic tuning of biquadratic exchange coupling in magnetic thin films

The effective interlayer coupling between antiferromagnetically coupled hard and soft ferromagnetic thin films is investigated as a function of the magnetic bit length in the hard layer, which is controlled using a magnetic recording system. The interlayer coupling is explored by studying the magnetization reversal of the soft layer. As the bit length decreases, the coupling evolves from antiferromagnetic to biquadratic to uncoupled. These results are reproduced using a micromagnetic model and determine the applicability range of Slonczewski's fluctuation model of biquadratic coupling.     

涂覆聚甲基丙酸甲酯的磁性膜外磁场作用下的往复滑动摩擦行为研究

磁性材料被广泛应用于磁记录和磁润滑等领域,聚甲基丙烯酸甲酯因其良好的介电性,能够用作磁性材料的表面涂层.本文对外磁场作用下,外加载荷和磁场强度对往复滑动的聚甲基丙烯酸甲酯/磁性薄膜双膜系摩擦性能的影响开展了研究.实验结果表明:聚甲基丙烯酸甲酯/磁性双膜体系的摩擦性能随载荷和磁场强度改变而变化;但在干摩擦和硅油润滑两种模式下,磁场对其摩擦学性能的影响规律不同.理论分析了磁场作用下磁场诱发的磁性力与摩擦副物理性质变化对摩擦力和摩擦系数的影响,与实验结果符合良好.研究结果为磁性薄膜的界面介质设计与控制提供了依据.     

Magnetic resonance studies of three-layer FeNi/Bi/FeNi films

The interlayer coupling in three-layer FeNi/Bi/FeNi films is studied by electron magnetic resonance. The magnetic anisotropy at the permalloy–bismuth interface is shown to play a significant role in the formation of the magnetic state of the film structure. The interlayer coupling oscillation period is found to be about 8 nm. The interlayer coupling and the interface anisotropy and their temperature dependences are determined.     

Interfacial roughness and temperature effects on exchange bias properties in coupled ferromagnetic/antiferromagnetic bilayers

Monte Carlo simulations have been used to study the relationship between the exchange bias properties and the interface roughness in coupled ferromagnetic/antiferromagnetic (FM/AFM) films of classical Heisenberg spins. It is shown that the variation of the exchange bias field versus the AFM anisotropy strongly depends on the FM/AFM interface. Unlike the flat interface, a non-monotonic dependence is observed for the roughest FM/AFM interface. This is explained by canted magnetic configurations at the FM/AFM interface, which appear after the first reversal due to the magnetic frustration. The temperature dependence of the exchange field is also dependent on the roughness. While the exchange field is roughly constant for the flat interface, a decrease is observed for the roughest interface as the temperature increases. This has been interpreted as a significant decrease of the effective coupling between the FM and the AFM due to the disordering of the moments at the FM/AFM interface because of the combination of magnetic frustration and temperature activation.     

Si-Al2O3复合薄膜的室温铁磁性

在Si-Al₂O₃复合薄膜中观察到室温铁磁性.Si的体积百分比为15 %的Si-Al₂O₃复合薄膜的磁性最强.Si的含量影响样品的磁有序,在样品中观察到了明显的磁畴.在不同气氛下,对样品进行快速热退火.退火样品的磁性测试结果的差别表明氧空位不是样品铁磁性的主要来源.我们认为铁磁性来源于Si与Al₂O₃基质界面之间的缺陷的磁耦合.改变Si的含量可以改变缺陷密度,从而控制铁磁耦合强度. 关键词： 2O₃薄膜')" href="#">Al₂O₃薄膜 室温铁磁性 掺杂 交换相互作用     

The spin-wave contribution to the heat capacity of ferromagnetic thin films with variable interlayer couplings

A Heisenberg model is solved within the spin-wave theory for thin films in which ferromagnetic monolayers are separated by nonmagnetic spacer layers. The interface interaction is assumed to be ferromagnetic. We have included also a magnetic anisotropy in each manolayer. The temperature dependence of the spin-wave contribution to the heat capacity C _m in such composite systems is derived for different interlayer couplings and for different film thickness.     

Dependence of the ferromagnetic resonance modes on the coupling strength in exchange-coupled trilayer structures

The dependence of the dispersion relation and the magnetization on the exchange coupling strength was calculated for a system consisting of two ferromagnetic layers exchange-coupled through a nonmagnetic spacer layer. The magnetic layers are characterized by both uniaxial and cubic magnetocrystalline anisotropies. A minimization procedure was developed which allows the resonance modes to be obtained for any magnetic field orientation and strength, as well as for any exchange coupling strength. If the antiparallel coupled film is unsaturated at resonance, the dispersion relation for both acoustic and optic modes could be rather complex, especially when the field is applied in the plane of the film.     

First-principles study of ferromagnetism in epitaxial Si-Mn thin films on Si(001)

Density-functional theory calculations are employed to investigate both the epitaxial growth and the magnetic properties of thin Mn and MnSi films on Si(001). For single Mn adatoms, we find a preference for the second-layer interstitial site. While a monolayer Mn film is energetically unfavorable, a capping-Si layer significantly enhances the thermodynamic stability and induces a change from antiferromagnetic to ferromagnetic order. For higher Mn coverage, a sandwiched Si-Mn thin film (with CsCl-like crystal structure) is found to be the most stable epitaxial structure. We attribute the strong ferromagnetic intralayer coupling in these films to Mn 3d-Si 3s3p exchange.     

Effects of thin MnAl buffer layer on structural and magnetic properties of MnAl films

Thin Mn(2 nm)/Al(2 nm) bilayers serving as buffer layers have been prepared prior to the deposition of MnAl films. The ferromagnetic τ-phase forms in the buffer layers at an optimum substrate temperature. As a template it induces the growth of following MnAl film. Compared with the case of film without buffer layer, the growth of non-ferromagnetic phase is suppressed and the structural and magnetic properties of MnAl film are improved. Weak dipolar inter-grain coupling is revealed in the MnAl film, and the magnetic reversal process is dominated by magnetic moment rotation.     

Monte Carlo study on bilayer thin films magnetic properties dependence with discontinouos anisotropy parameters

In the last few years there has been significant interest in the field of thin films, due to numerous specific phenomena related to the low dimension of these systems, and to the large opportunities in development of high technologies based on their specific magnetic and electronic properties. When dealing with systems of reduced dimensionality it is important to take into account the influence of magnetic anisotropies. In this paper we investigate the magnetic properties of bilayer thin film. This behavior is modeled using Monte Carlo simulations, in the Extended Anisotropic Heisenberg Model. The magnetization, out-of-plane and in-plane magnetic susceptibilities, and also the specific heat bearings according to temperature are investigated in order to find the potential magnetic ordering phases and the critical temperatures, for two sets parameter assignments. For quasi-uniform anisotropy parameters of the film we detect the ferromagnetism-paramagnetism transition and then, by changing the model parameters values, we relieve a short range ferromagnetic ordering phase arising from the antiferromagnetic base layer coupling influence and from easy-plane anisotropy discontinuity on the layers interface.      

BaTiO_3/La_(0.67)Sr_(0.33)MnO_(3-δ)复合薄膜的磁致电极化和磁介电特性研究

采用脉冲激光沉积法制备了BaTiO_3(BTO)与缺氧的铁磁绝缘态La_(0.67)Sr_(0.33)MnO_(3-δ)(LSMO)构成的磁电复合薄膜,研究了20—300K温度区间内磁场对电极化特性和介电特性的影响.研究发现,施加磁场使得电滞回线的剩余极化强度和矫顽场均增大,其变化率峰值分别为111.9%和89.6%,峰值温度分别为40K和60K.异质结具有显著的磁介电效应,在测量温度区间内,磁场使得介电常数增大,介电损耗减小.在0.8T场强下,介电常数的最大磁致变化率出现在60K,达到了300%,而介电损耗也在此温度实现了最大变化,减小为零场时的50.9%.该磁电复合薄膜的磁致电极化和磁介电特性的极值均出现在LSMO层的磁电阻峰值温度附近,这说明磁场对电滞回线和介电参数的调制应该源自电荷相关的耦合作用.其可能的机理是磁场使得锰氧化物中的Mn离子局域磁矩趋于有序排列,并通过自旋-轨道耦合以及界面效应间接影响了BTO的电极化特性.研究结果对于多铁器件的开发和应用具有重要意义.     

Electronic and magnetic properties of ultrathin films and interfaces investigated by dichroic core-level photoelectron spectroscopy

The electronic and magnetic structures of ultrathin films made of a ferromagnetic and a nonmagnetic material are theoretically investigated by means of magnetic dichroism in spin- and angle-resolved core-level photoelectron spectroscopy. How these properties manifest themselves in the photoemission intensities is analyzed with a focus on the interface between film and substrate. The dependence on both exchange and spin–orbit splitting, magnetic ordering, core-level shift and on the thickness of the covering layer are investigated in detail. Ultrathin films of Fe and Pd serve as prototypical systems because of their large exchange and spin–orbit splittings, respectively.     

Nanomechanical magnetization reversal

The dynamics of the ferromagnetic order parameter in thin magnetic films is strongly affected by the magnetomechanical coupling at certain resonance frequencies. By solving the equation of motion of the coupled mechanical and magnetic degrees of freedom we show that the magnetic field induced magnetization switching can be strongly accelerated by the lattice and illustrate the possibility of magnetization reversal by mechanical actuation.     

Magnon spectrum of a symmetric-spin nanocontact on a ferromagnetic ultrathin film

A theoretical model is presented for the study of the magnetic properties and the coherent magnon transport via monatomic chains in ultrathin magnetic films. In particular, we studied a finite number of monatomic chains joining two slabs of ferromagnetic material. Each slab consists of five atomic layers of a cubic lattice with magnetically ordered spins coupled by the Heisenberg exchange. The system is supported on a non-magnetic substrate and otherwise considered free from magnetic interactions. The spin dynamics of the ultrathin film is studied by the matching method. The individual and the total magnon transmissions of the ultrathin ferromagnetic film, scattering coherently at the nanojunction zone, and the localized spin states in the boundary domain are calculated and analyzed. The interatomic magnetic exchange is varied on the boundary domain specifically for three cases of magnetic exchange to investigate the consequences of magnetic softening and hardening for the calculated properties. Numerical results show characteristic interference effects between the incident spinwaves and the localized spin states of the nanocontact. The calculated properties are presented for arbitrary incidence of the magnons on the boundary, for all accessible frequencies in the propagating bands, and for the interatomic magnetic exchange of the magnetic film. The localized magnon branches created by the nanocontact domain are observed in the Brillouin zone.     

Dense stripe domains in a nanocrystalline CoFeSiB thin film

We recently reported a possible antiferromagnetically coupled phase in a Co-rich CoFeSiB thin film, that had a partially nanocrystalline Co phase in an amorphous CoFeSiB matrix. Although an amorphous CoFeSiB film should show a ferromagnetic behavior, we observed an antiferromagnetic coupling associated with a nanocrystalline Co phase in the hysteresis-loop measurements of Co-rich CoFeSiB thin films. We ascribed the observed antiferromagnetic coupling to dense stripe domains consisting of periodically up and down domains perpendicular to the surface of the film. The configuration of the stripe domains was confirmed with magnetic force microscopy images. When a longitudinal magnetic field was applied, the size of the stripe domain was reduced. While for a transverse field, the domain structure became tilted and zigzagged, but no in-plane magnetic anisotropy was noted. When the magnetic field was increased to values above the saturation magnetic field, H_S = 2.5 kOe, the domain structure disappeared.