Uniaxial Anisotropy Field Research Articles

Enhancing High-Frequency Properties of Nanocrystalline Sputtered Fe Thin Films by Using MnIr Underlayer and Oblique Deposition

In this work, the single-layer Fe and the bilayer MnIr/Fe thin films were fabricated on Si (100) substrate using the oblique-angle sputtering technique. The structure and magnetic properties of the as-deposited films were investigated. MnIr biased layer deposited at the normal incidence angle develops an exchange bias field of 5.2 Oe which leads to an increase in the uniaxial anisotropy field of Fe layer from 4.36 to 23.66 Oe and the ferromagnetic resonance frequency from 1.02 to 1.46 GHz. It is also found that the resonance frequency of the bilayer MnIr/Fe rises sharply from 1.46 to 5.05 GHz as the incident angle increases from 0 to 36°.

Micromagnetic Analysis of Edge Effects in a Thin Magnetic Film during Local Excitation of Magnetization Oscillations

The method of numerical micromagnetic simulation was used to study the magnetization dynamics of a thin film with uniaxial magnetic anisotropy during ferromagnetic resonance (FMR) excitation in it on the local sites by a linearly polarized high-frequency magnetic field emitted from the 1 mm opening in the metallic screen of the transmission line. It was established that non-uniformities of demagnetizing fields emerging near the film edges lead not only to the change in the FMR field, but also to the change in the value and direction of the uniaxial anisotropy field. The distribution of non-uniformities of the magnetic anisotropy characteristics over the area of 60 nm thick permalloy film that was measured on the scanning FMR spectrometer agrees well with the micromagnetic simulation results. Demagnetizing fields were proved to be the main cause for the edge effects in magnetic films.

Yu-Shiba-Rusinov states of a single magnetic molecule in ans-wave superconductor

We use the numerical renormalization group theory to investigate the Yu-Shiba-Rusinov (YSR) bound state properties of single magnetic molecules placed in an s-wave superconducting substrate. The molecule consist of a large core spin and a single orbital, coupled via an exchange interaction. The critical Coulomb interaction for the singlet/doublet transition decreases in the presence of this exchange interaction for both ferro and anti-ferromagnetic couplings. The number of YSR states also increase to two pairs, however, in the singlet phase, one of the pairs have zero spectral weight. We explore the evolution of the in-gap states using the Anderson model. Away from the particle-hole symmetry point, the results suggest a doublet-singlet-doublet transition as the on-site energy is lowered while keeping the Coulomb interaction fixed. To understand these results, we write down an effective model for the molecule in the limit of large superconducting order parameter. Qualitatively, it explains the various phase transitions and spectral nature of the in-gap states. Finally, we analyze the effects of magnetic anisotropic fields of the core spin on in-gap states. Due to internal degrees of freedom of the spin excited states, a multitude of new states emerges within the gap. Depending on the sign and strength of the uniaxial anisotropic field, the results indicate up to three pairs of YSR states.

Magneto-optical Kerr microscopy investigation of magnetization reversal in Co2FeSi Heusler alloy thin films

Magneto-optical Kerr effect microscopy investigation of magnetocrystalline anisotropy and the magnetization reversal (MR) process in Co2FeSi (CFS) Heusler alloy thin films reveals the following: Regardless of the strength of the anti-site atomic disorder, all CFS films of fixed thickness (t = 50 nm) exhibit variations in the remanent magnetization (Mr) and coercive field (Hc) with the “in-plane” magnetic field (H) angle, φH, that are characteristic of the “in-plane” uniaxial anisotropy (UA) with an easy axis along φH = 0°. The observed variations with the field-angle are well described by the two-phase pinning (TP) model. Exceptions to this rule are the films with t ≥ 25 nm, having a maximum B2 atomic order, which show completely different angular variations in Mr and Hc. In such exceptional cases, we find that the TP model reproduces Mr(φH) and Hc(φH) only when it takes into account two mutually exclusive UAs, UA1 and UA2, with easy axes perpendicular to one another and UA1 ≫ UA2. When H points along the easy axis (φH = 0°), MR in all CFS films proceeds through the nucleation of reverse domains and their subsequent growth by domain wall movement as H increases. Atomic disorder has essentially no effect on the MR process, but the domain wall pinning at defects/imperfections affects the magnitudes of Hc and the UA field, Hk. At φH ≃ 45°, MR takes place through the formation of ripple domains. As H increases, the reverse domains grow at the expense of ripple domains, and a single domain configuration is established at high fields. When φH = 90°, MR in all films involves nucleation and subsequent growth of reverse domains by the field-induced movement of the 180° domain walls.

Magnetic Properties of Permalloy Thin Film Edges

The paper presents the results of ferromagnetic resonance (FMR) spectrometry of magnetic properties of nanocrystalline thin films obtained by magnetron sputtering of permalloy targets of various composition (NixFe1–x, x = 0.6–0.85). The behavior of the main magnetic properties of the thin film edges is analyzed. Near the film edges, not only the fluctuation of the uniaxial magnetic anisotropy field is observed, but also a drastic widening of the FMR line and the decrease in the effective saturation magnetization.

Large anisotropy of magnetic damping in ultrathin epitaxial Fe/GaAs (0 0 1) film

The magnetization dynamics of ultrathin epitaxial Fe films on GaAs (0 0 1) with different thicknesses have been investigated by all-optical time-resolved magneto-optical Kerr effect. For the Fe film with thickness of 8 monolayers, the magnetic damping constant along orientation increases by 66% compared with that along orientation, showing the uniaxial anisotropy of magnetic damping. By the measurement of angular dependent time-resolved magneto-optical Kerr effect, the uniaxial magnetic damping is clearly correlated to the in-plane uniaxial anisotropy field of the Fe film. In addition, the anisotropy of the damping constants is found to disappear for the Fe films thicker than 15 monolayers, suggesting that the anisotropic damping originates from the interfacial effect between Fe and GaAs.

Crystallographically textured Ba0.8La0.2Fe11.8-xCu0.2O19-δ hexaferrites with narrow FMR linewidth

M-type hexaferrites which exhibit strong uniaxial anisotropy field, are promising for the applications in self-biased microwave and millimeter wave (MMW) devices. Here we demonstrate crystallographically textured hexaferrites with narrow ferromagnetic resonance (FMR) linewidth synthesized by the conventional ceramic method. Meanwhile, the relationship between iron-deficiency content and microstructure, crystallographic, and magnetic properties are researched. These hexaferrites have strong remanence ratio of above 0.9 along c-axis. By fitting of Lorentzian function to absorption derivative, we probe detailedly into the zero-field FMR linewidth of Ba0.8La0.2Fe11.8-xCu0.2O19-δ hexaferrites. When x equals 1.0, it indicates the narrowest FMR linewidth of 324Oe, as compared with previous reports for crystallographically textured hexaferrites.

Experimental study of the magnetic characteristics of nanocrystalline thin films: the role of edge effects

Magnetic characteristics and their spatial distribution of magnetron sputtered nanocrystalline NiFe thin films of various compositions were investigated by ferromagnetic resonance (FMR) and magneto-optical Kerr effect microscopy. A sharp increase in the FMR linewidth and a strong deviation of the uniaxial magnetic anisotropy field were observed near the film edges. It was shown that the observed magnetic anisotropy behavior can be explained by assuming that besides the field-induced uniaxial magnetic anisotropy an additional source of the uniaxial anisotropy near the film edges exists, with the easy axis parallel to the edges. The possible origins of this additional contribution were discussed.

Dynamics of Magnetization in Multilayer TbCo / FeCo Structures under the Influence of Femtosecond Optical Excitation

The need to study ultrafast processes in magnetism is due to the prospects for creating ultrafast magnetic recording and ultrafast spintronic devices. In order to excite the magnetic subsystem femtosecond optical pulses are used. The excitement is manifested as in spin precession. In metals, the material is heated first due to significant optical absorption, and significant Joule losses occur. The most important task is to search for materials in which spin processes are excited without heating. Obvious candidates are weakly absorbing materials, such as ferrite garnets. However, the range of such materials and the range of their functionality are limited.The purpose of this work is to study the dynamics of systems with nonthermal mechanisms of spin precession excitation. Such excitation is possible in ferromagnetic / antiferromagnetic heterostructures with exchange interaction, provided that the recombination time of photocarriers is shorter than the time of heat diffusion. Multilayer TbCo / FeCo structures of the near IR range were investigated for a femtosecond optical pulse. The spin dynamics are compared with the direction of the wave vector of the exciting pulse along and perpendicular to the axis of easy magnetization of the structures (“easy axis” and “hard axis” geometry, respectively). It is shown that in case of “easy axis” geometry the determinative mechanism is the thermal interaction. When the system is exposed to an excitation pulse, this mechanism leads to a decrease in the projection of magnetization on the direction of propagation of the test beam. In case of “hard axis” geometry, the magnetization turns to the magnetic field at the initial stage. Then it precesses and relaxes to an equilibrium angular orientation. Such dynamics indicate a rapid recovery of the uniaxial anisotropy field after laser irradiation. The presented results demonstrate an ultrafast change in the magnetic anisotropy induced during the fabrication of the heterostructure under study, which may be of interest for optical control of the orientation of the magnetization.

Uniaxial anisotropy, intrinsic and extrinsic damping in Co2FeSi Heusler alloy thin films

Ferromagnetic resonance (FMR) technique has been used to study the magnetization relaxation processes and magnetic anisotropy in two different series of the Co2FeSi (CFS) Heusler alloy thin films, deposited on the Si (1 1 1) substrate by ultra high vacuum magnetron sputtering. While the CFS films of fixed (50 nm) thickness, deposited at different substrate temperatures (TS) ranging from room temperature (RT) to 600°C, constitute the series-I, the CFS films with thickness t varying from 12 nm to 100 nm and deposited at 550°C make up the series-II. In series-I, the CFS films deposited at TS = RT and 200°C are completely amorphous, the one at C is partially crystalline, and those at C, 550°C and 600°C are completely crystalline with B2 order. By contrast, all the CFS films in series-II are in the fully-developed B2 crystalline state. Irrespective of the strength of disorder and film thickness, angular variation of the resonance field in the film plane unambiguously establishes the presence of global ‘in-plane’ uniaxial anisotropy. The uniaxial anisotropy field decreases as the crystalline order in the films increases and goes through a minimum at t = 50 nm as a function of film thickness. Landau–Lifshitz–Gilbert damping and two-magnon scattering dominantly contribute to the line-broadening in both ‘in-plane’ and ‘out-of-plane’ configurations. The two-magnon scattering has larger magnitude in the amorphous films than in the crystalline ones. Angular variation of the linewidth in the film plane reveals that, in the CFS thin films of varying thickness, a crossover from the ‘in-plane’ local four-fold symmetry (cubic anisotropy) to local two-fold symmetry (uniaxial anisotropy) occurs as t exceeds 50 nm. Gilbert damping constant decreases monotonously from 0.047 to 0.0078 with decreasing disorder strength (increasing TS) and jumps from 0.008 for the CFS film with t = 50 nm to 0.024 for the film with t = 75 nm. Such variations of with TS and t are understood in terms of the changes in the total (spin-up and spin-down) density of states at the Fermi level caused by the disorder and film thickness. Spin pumping across the Co2FeSi film/Ta cap-layer interface makes negligible contribution to . We propose that disorder and/or the film thickness can be used as control parameters to tune , whose value is decisive in choosing a ferromagnetic film for a given spintronics application.

Large tunability of frequency in Fe0.5Co0.5-ZnO/PZN-PT nanogranular films with high resistivity

Abstract The soft magnetic films (SMFs) using in monolithic microwave integrated circuits (MMICs) are suffered from the lower ferromagnetic resonance frequency f FMR and resistivity. In this study, Fe0.5Co0.5-ZnO films with high resistivity were fabricated by a compositional gradient sputtering on (0 1 1) lead zinc niobate–lead titanate (PZN-PT) substrates. It is interesting to note that the resistivity of the ZnO-doped Fe0.5Co0.5 films is 10–30 times larger than that of pure Fe0.5Co0.5 films. An ultrahigh f FMR of 10.48 GHz were achieved at electric field of 8 kV/cm without bias magnetic field. The excellent microwave ferromagnetic performances in as-deposited films can be attributed to two reasons: (1) the large uniaxial anisotropy field induced by gradient composition of doping ZnO, (2) the strong magnetoelectric coupling between the ferromagnetic/ferrielectric interfaces under the condition of high resistivity in Fe0.5Co0.5-ZnO films.

A sum rule of uniaxial anisotropy and external magnetic field for formation of Néel-type skyrmion lattices in two-dimensional ferromagnets

It is generally believed that the perpendicular magnetic anisotropy (PMA) plays an important role in stabilizing skyrmion lattices (SkL) in two-dimensional (2D) magnetic systems in which both Heisenberg exchange and Dzyaloshinskii–Moriya interactions co-exist, and the skyrmion sizes in SkLs are mainly determined by the strengths of these two intrinsic interactions. To investigate the details, we employ here a quantum computational approach we develop in recent years to simulate the Néel-type skyrmion lattices formed on a 2D PdFe/Ir(1 1 1)-like film. From our simulated results, we find that: within an external magnetic field applied normal to the film plane, the PMA is indeed able to help induce Néel-type SkLs in a wider field range; however, to stabilize the SkLs, the PMA cannot be too strong, the strengths of the external magnetic field and the maximal PMA must satisfy a sum rule since the effective perpendicular magnetic field generated by these two interactions cannot exceed a largest value. We also notice that the periodical boundary condition imposed on the FM system in simulations is able to facilitate SkL formations, and it can also modify the skyrmion size in a certain extend.

Annealing influence on magnetic anisotropies of CoFe thin films

Post-annealing effect on the magnetic anisotropies of cubic CoFe films epitaxially grown on MgO (001) substrates are investigated. X-ray diffraction patterns reveal that the crystallization degree gradually improves with the increase of annealing temperature (Ta), which results in obvious enhancement in both the uniaxial (HU) and biaxial magnetic anisotropy fields. Magnetic hysteresis loops of the unannealed sample show two equivalent easy axes along the CoFe [110] and [11¯0] directions, being in accord with the observed fourfold symmetry of angular remanent magnetization (ARM) curve. Nevertheless, with the increase of Ta, the two easy axis loops become inequivalent due to the increased HU along [110] direction, thus giving rise to a two-step switching behavior for the [11¯0] direction loop at Ta>350°C and the ARM curve transformation from fourfold to twofold symmetry. This work provides a deep insight and an effective approach to control the magnetic anisotropies and magnetization states for practical applications.

Hexagonal barium ferrite films on a Pt(1 1 1)/Si(0 0 1) substrate and their local magnetic properties

Abstract Hexagonal barium ferrite films were deposited on Pt(1 1 1)/Si(0 0 1) substrates by pulsed laser deposition. This paper presents an investigation of the crystal structure, morphology and local magnetic properties of the deposited films. The characterization results demonstrated orientation and morphological dependences on the Pt thickness and annealing temperature. A film prepared with a 200-nm-thick Pt buffer layer and an annealing temperature of 900 °C exhibited oriented platelet grains with a mean diameter of ∼400 nm and excellent magnetic properties with a saturation magnetization of ∼311 emu/cm3, a uniaxial anisotropy field of ∼15.5 kOe and a remanent squareness in the out-of-plane direction of ∼68.6%. Furthermore, a first-order reversal curve (FORC) diagram showed that the film had a positive mean interaction field (Hu) between particles and broad distributions of coercivity (Hc) centred at Hu = 600 Oe and Hc = 2500 Oe.

Fabrication and ferromagnetic resonance study of BZT-BCT/LSMO heterostructure films on LAO and Pt

Abstract In this article, dynamic magnetic properties of La0.7Sr0.3MnO3 (LSMO) thin film capped with a Pb-free ferroelectric BZT-BCT layer deposited on two different substrates, i.e. lanthanum aluminate (LAO) and Platinum (Pt), by pulsed laser deposition (PLD) have been investigated using ferromagnetic resonance (FMR) spectroscopy. The heterostructures of BZT-BCT/LSMO on LAO substrate were highly (0 0 l)-oriented whereas these were randomly oriented on Pt substrate. The well-behaved M-H hysteresis loops were observed at room temperature for both heterostructures indicating the ferromagnetic behavior of LSMO. The right shift of the hysteresis loop of the heterostructure was observed due to the magnetoelectric coupling between ferroelectric and ferromagnetic layers. The FMR measurements yield optimum values of different important parameters such as the linewidth offset, Gilbert damping, gyromagnetic ratio, and in-plane uniaxial anisotropy field of the thin films, which are essential to design spin valve and magnetic tunneling based devices. We found the lowest Gilbert damping parameter of ∼0.03 for the BZT-BCT/LSMO/LAO heterostructure due to spin orbit coupling. In addition, the gyromagnetic ratio was also obtained to be small (0.002 GHz/Oe) in the same film. These results open new possibilities to use BZT-BCT/LSMO heterostructure for future spintronic device applications.

Specific Features of the Magnetic Anisotropy of Thin Yttrium Iron Garnet Films Prepared by Pulsed Laser Deposition

The specific features of dependences of the magnetic anisotropy constants on the thickness of yttrium iron garnet films prepared by pulsed laser deposition were studied. Films with thicknesses of 96–333 nm were produced by pulsed laser evaporation of the target material and deposition onto gadolinium-gallium-garnet substrates with the (111) orientation. The results of an investigation into static magnetic properties showed that the saturation magnetization decreases as the films get thinner. The high-frequency properties were studied by ferromagnetic resonance (FMR). The uniaxial and cubic anisotropy fields and the relaxation parameter were determined by analyzing the angular dependences of the resonance field and the FMR line width. It was found that as the thickness decreases, the strength of the uniaxial anisotropy field increases monotonically, while the cubic anisotropy field decreases and reverses its sign.

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Effect of Annealing on the Structural and FMR Properties of Epitaxial YIG Thin Films Grown by RF Magnetron Sputtering

Calculations of surface spin dynamics associated with biquadratic exchange and uniaxial anisotropy field in (S > 1) heisenberg ferromagnet by means of matching procedure.

Calculations within framework of both non-interacting spin-wave theory and random phase approximation have been carried out to investigate elementary magnetic excitations by scanning the occurrence of localized modes associated with surface spin dynamics. Mean field approximation and single spin-wave function theory in the context of semi-infinite Heisenberg ferromagnet are exploited. We exploit the mathematical formalism of matching method which starting from secular equation of spin motion established for the bulk of semi-infinite structure will make it possible to describe the symmetry properties of propagating (evanescent) precessional fields in parallel (perpendicular) direction to surface terrace. The localized states associated with surface are obtained by matching the properties of quantized propagating modes with evanescent modes occurring in vicinity of surface region. This mathematical procedure allows treating the continuity equations for spin precessional field amplitude operating in the border bulk media-surface region from their special suitable symmetry properties related to those induced by the broken translational symmetry arising from the existence of surface. The solutions are described considering the presence of uniaxial anisotropy field and biquadratic exchange as well as magnetic anisotropy field. The focus is on the existence, the nature as well as on the form and stability of localized surface modes. Also, obtained solutions are discussed qualitatively by observing the response of energy branches to the variation of strength of biquadratic exchange term and surface anisotropy field as well as magnetic exchange parameters occurring on the surface domain. Numerical examples of the localized modes energies associated with the surface are shown and they are found to exhibit various effects due to the strength of biquadratic exchange and magnetic anisotropy field under certain circumstances. The analytical formulation exposed in this work and its methodology based solely on the symmetry properties as well as the qualitative agreement describing our results with those obtained in the literature provide a considerable contribution to the surface spin dynamics calculations under the influence of biquadratic coupling and uniaxial anisotropy term. Moreover, the results obtained through matching procedure make it possible to remove an ambiguity concerning the existing disparities in analysis and interpretation of the main results already reported in literature.

Some explicit solutions of the Landau‐Lifshitz equation for anisotropic ferromagnets

The aim of this paper is to construct explicit solutions of the Landau‐Lifshitz equation for anisotropic ferromagnets. Firstly, we present some explicit solutions for n‐dimensional Landau‐Lifshitz equation with a generalized uniaxial anisotropy field (depending only on time) under a suitable transformation, where the generalized uniaxial anisotropy field contains the classical easy‐axis case and the important higher‐order approximations. Some relevant examples are indicated that contains the cubic system proposed by Landau and Lifshitz in 1960. Secondly, an explicit plane‐wave solution of Landau‐Lifshitz equation for the completely anisotropic case is obtained. Finally, some properties of magnetization for ferromagnets are provided by analysis of the solutions.

Influence of Deposition Cycle and Magnetic Annealing on High-Frequency Magnetic Properties of the [Co90Fe10/Ta]<italic>n</italic> Multilayer Thin Films

In this paper, a series of [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> multilayer thin films with various deposition cycles n were prepared by magnetron sputtering. The crystal structure, top-surface topography, and static and dynamic magnetic properties of [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> multilayer thin films were investigated systematically. The results showed that the deposition cycle n has slight impact on the high-frequency magnetic performance of the multilayer thin films except damping coefficient α and real part of permeability μ'. Moreover, we studied the influence of magnetic annealing temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> ) on high-frequency soft magnetic properties of [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> multilayer thin films. It was found that saturation magnetization, coercivity, in-plane uniaxial magnetic anisotropy field, damping coefficient, and real part of permeability were all highly dependent on T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> . When T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> = 250 °C, the [Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /Ta] <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> multilayer thin film exhibited a relatively good comprehensive performance: saturation magnetization 4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> = 13.06 kG, in-plane uniaxial magnetic anisotropy fields H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> = 42 Oe, easy-axis coercivity H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> = 2.8 Oe, ferromagnetic resonance frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 2.25 GHz, and real permeability μ' = 255.