磁性多层薄膜中交换各向异性研究

采用铁磁共振理论研究了自旋阀体系中交换各向异性场和两铁磁薄膜厚度对体系性质的影响,得到系统色散关系的解析表达式.研究表明:体系中存在的交换各向异性场H_E对声学模和光学模的共振场均有影响(其对声学模的影响较大).而且还发现声学模共振场随A,B层铁磁薄膜厚度的变化关系依赖于系统中交换各项异性场的强弱;相反,光学模共振场随两铁磁层厚度的增加始终增强.     

Magnetization of thin films of ferromagnetic superconductors

The magnetization of thin films of ferromagnetic superconductors is theoretically studied. The symmetric and antisymmetric magnetic orders appear in the films depending on the thickness of the films. The magnetization for the symmetric order monotonically increases with decreasing temperature. However, the magnetization curves for the antisymmetric order has a sharp peak near the magnetic phase transition temperature in a weak external magnetic field.     

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.     

Exchange couplings in magnetic films

Recent advances in the study of exchange couplings in magnetic films are introduced.To provide a comprehensive understanding of exchange coupling,we have designed different bilayers,trilayers and multilayers,such as anisotropic hard/soft-magnetic multilayer films,ferromagnetic/antiferromagnetic/ferromagnetic trilayers,[Pt/Co]/NiFe/NiO heterostructures,Co/NiO and Co/NiO/Fe trilayers on an anodic aluminum oxide(AAO) template.The exchange-coupling interaction between soft-and hard-magnetic phases,interlayer and interfacial exchange couplings and magnetic and magnetotransport properties in these magnetic films have been investigated in detail by adjusting the magnetic anisotropy of ferromagnetic layers and by changing the thickness of the spacer layer,ferromagnetic layer,and antiferromagnetic layer.Some particular physical phenomena have been observed and explained.     

Ultrathin Co/Cu(110) film as a lattice of ferromagnetic grains with dipolar interaction

The well-known fact of magnetic ordering in ultrathin Co films (with an effective thickness of several monoatomic layers) on a single-crystal Cu(110) substrate is described quantitatively using the model according to which the thin film is a lattice of three-dimensional ferromagnetic grains with dipole-dipole interactions. The critical film thickness corresponding to the ferromagnetic transition and the corresponding Curie temperature were calculated.     

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.     

Crystallographic structure of ultrathin Fe films on Cu(100)

We report the observation of bcc-like crystal structures in 2-4 monolayer (ML) Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The nonpseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness, is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.     

Ferromagnetic resonance in epitaxial films of uniaxial barium hexaferrites

The magnetic parameters of epitaxial barium hexaferrite films are studied. The hysteresis of the field and frequency dependences of ferromagnetic resonance in the films is investigated in the ranges of the multidomain-monodomain and monodomain-multidomain transitions. The effect of the substrate thickness on film-microwave field interaction is examined.     

Experiments on the reflection of cold atoms from magnetic thin films

We report the results from a series of experiments in which ferromagnetic thin films were used as atom mirrors for laser-cooled rubidium atoms released from a magneto-optical trap. The thin films were made of cobalt and lanthanum calcium manganite (LCMO) with thicknesses between 20 and 300 nm. The magnetic domains in these thin films have a periodic structure where the spatial period is of the order of the thickness of the film, and the field decays exponentially above the film over a length scale comparable to the domain size. Thus, the neutral atoms reflect off these films from distances comparable to the thickness of the film, resulting in modification of the reflectivity due to the competition between the repulsive magnetic force and the attractive short-range forces such as van der Waals and Casimir forces. The smoothness of the atom mirror is also modified due to the proximity of the magnetic domains. The reflectivity is sensitive to the domain structure and size, which can be modified in LCMO by applying a modest external magnetic field. In this paper, we discuss the evaluation of the thin films as magnetic mirrors for atom optics, and the measurement of the van der Waals force with an accuracy of about 15%, using cobalt thin films. We also discuss some preliminary results on the temperature-dependent reflectivity for atoms near the ferromagnetic transition at 250 K in the LCMO film, and on the domain dynamics and relaxation.     

Magnetic field dependence of the dynamical properties of ferromagnetic semiconducting thin films

The effect of external magnetic field, temperature and film thickness on the spin wave energy and the spin-wave damping in thin ferromagnetic semiconducting films is studied using the s-d interaction model and a Green's function formalism beyond the random phase approximation.     

Thickness dependent magnetic and ferroelectric properties of LaNiO3 buffered BiFeO3 thin films

BiFeO₃ (BFO) thin films with thickness increasing from 40 to 480 nm were successfully grown on LaNiO₃ (LNO) buffered Pt/Ti/SiO₂/Si(100) substrate and the effects of thickness evolution on magnetic and ferroelectric properties are investigated. The LNO buffer layer promotes the growth and crystallization of BFO thin films. Highly (100) orientation is induced for all BFO films regardless of the film thickness together with the dense microstructure. All BFO films exhibited weak ferromagnetic response at room temperature and saturation magnetization is found to decrease with increase in film thickness. Well saturated ferroelectric hysteresis loops were obtained for thicker films; however, the leakage current dominated the ferroelectric properties in thinner films. The leakage current density decreased by three orders of magnitude for 335 nm film compared to 40 nm film, giving rise to enhanced ferroelectric properties for thicker films. The mechanisms for the evolution of ferromagnetic and ferroelectric characteristics are discussed.     

Finite size effect and phase diagram of ultra-thin La0.7Sr0.3MnO3

La_0.7Sr_0.3MnO₃ (LSMO) ultra-thin films have been grown by pulsed laser deposition in conditions optimized for cation stoichiometry and bulk-like physical properties in the thick limit. Through electrical transport and magnetic measurements, a phase diagram is constructed as a function of film thickness. With decreasing thickness, the LSMO films cross over at high temperatures from a paramagnetic metal to a paramagnetic insulator, and at low temperatures from a ferromagnetic metal to a ferromagnetic insulator, in close similarity to that observed for varying the electronic bandwidth in bulk manganites.     

Dependence of magnetic properties on ferromagnetic layer thickness in trilayer Co/Ge/Co films with granular semiconducting spacer

We have investigated the magnetic properties of trilayer films of Co–Ge–Co. At a fixed thickness of germanium of 3.5 nm, the formation and distribution of metastable amorphous and cubic phases depends on the thickness of the ferromagnetic layer. The portion of the stable hexagonal phase is affected, too. Possible mechanisms for forming the observed magnetic structure are discussed.     

各向同性纳米结构Fe-Pt薄膜的结构和磁性

采用直流溅射和热处理技术制备了两个各向同性的纳米结构Fe-Pt永磁合金薄膜系列,并研究了它们的结构和磁性.研究表明,在富Fe双相纳米结构Fe-Pt永磁合金薄膜中,仅由硬磁的FePt相与软磁的Fe₃Pt相组成;在同一系列中,随Fe层厚度的增加,饱和磁极化强度和剩磁明显增大.由Kelly-Henkel图研究指出,在上述Fe-Pt纳米结构永磁合金薄膜中,磁相互作用主要由近邻纳米晶粒间的铁磁交换相互作用控制. 关键词： 磁性薄膜 纳米结构 矫顽力     

Peculiarities of the ferromagnetic resonance in multilayer CoFeZr-α-Si films

The static magnetic properties and ferromagnetic resonance spectra of multilayer CoFeZr-α-Si films with different numbers and thicknesses of magnetic and nonmagnetic layers have been investigated. It is established that the shape of the ferromagnetic resonance spectrum and the resonant fields H _res depend on the thickness of nonmagnetic layers and their total number. The character of changes in the spectrum makes it possible to estimate the quality of layers and interfaces.     

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.     

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.     

Local atomic structure of ultra-thin Fe films grown on Cu(100)

Ultra-thin epitaxial Fe films grown by thermal deposition on Cu(100) are analyzed by scanning tunneling microscopy. Evidence is presented that the morphological characteristics and magnetic properties are a direct consequence of FCC-to-BCC transitions reminiscent of those occurring in bulk Fe. In contrast to the assumption of a ferromagnetic FCC phase in previous models of the Fe/Cu(100) system, we observe a tightly twinned and strained BCC-like phase termed nanomartensite in films below 5 ML thickness, which encompasses almost the entire film volume of 3 ML films. In addition, the surface of 7–8 ML films reconstructs by forming non-close-packed structures with BCC-like bond angles. The formation of these BCC-like phases is the reason for the expansion of the interlayer spacing observed in these films and correlates perfectly with their ferromagnetic ordering. PACS 68.55.-a; 64.70.-p; 81.30.-t     

Thickness-dependent magnetic order and phase-transition dynamics in epitaxial Fe-rich FeRh thin films

The control of magnetic order and phase-transition dynamics by various means is a key towards low-power spintronics. Here, we report a control on magnetic order and phase-transition dynamics by tuning film thickness in epitaxial FeRh films. Reduction of film thicknesses from 200 nm to 5 nm results in an anti-ferromagnetic to ferromagnetic phase change, accompanied by a 0.55% lattice expansion for c-axis. The phase-transition dynamics is highly dependent on the film thickness, and involves the release and recovery of lattice strain that results in a lower transition temperature and larger thermal hysteresis in thinner films. The findings help to understand the origin of thermal hysteresis and phase-transition dynamics in ultra-thin FeRh films. Possible approaches to narrow down thermal hysteresis are proposed.     

Magnetization reversal observed by the deflection of magnetic actuator

A magnetic actuator consisting of a silicon oxide microcantilever and a silicon oxide plate deposited on ferromagnetic multilayer thin films is fabricated using electron beam lithography and electron beam evaporation, and placed in various magnetic fields to observe its flexure. The magnetic actuator is bent by magnetic torque produced by ferromagnetic multilayer thin films under an external magnetic field owing to the fabrication of a highly sensitive microcantilever and the design of elliptic ferromagnetic thin films with high magnetic shape anisotropy. The magnetic actuator is placed in four kinds of magnetic field directions to investigate the diversity of deflections; the angles between the easy axis of the ferromagnetic multilayer thin films and the direction of the external magnetic field are 90°, 70°, 45° and 20°.