Ferromagnetic Resonance Field Research Articles

Stress-induced controllable magnetic properties in flexible epitaxial Mn0.5Zn0.5Fe2O4 ferrite films

Flexible ferrite film has high potential applications in electronic skins and wearable devices. However, it is an enormous challenge to fabricate flexible ferrite film because of its high fragility. This work uses a novel etching sacrificial Sr3Al2O6 (SAO) layer to synthesize flexible Mn0.5Zn0.5Fe2O4 (MZFO) ferrite film. The MZFO film remains its single crystal structure after being transferred onto a flexible substrate. Owing to the great lattice mismatch between SAO and MZFO, the as-grown and transferred MZFO films exhibit the difference in magnetic properties, which is more sensitive along out-of-plane direction. The controllable magnetic properties of the film under the bending test are characterized by ferromagnetic resonance (FMR). A huge FMR field (Hr) shift of 704 Oe is achieved along out-of-plane direction when the bending radii are 5 mm. Meanwhile, the FMR linewidth (δH) of bent MZFO film (1267 Oe) is about 4 times higher than that of the unbent film (310 Oe). These controllable changes mainly come from the contribution of the two magnon scattering (TMS) effect. Finally, the Hr and δH almost return to their initial states when the stress is released, indicating a great recoverability.

Epitaxial lift-off of flexible single-crystal magnetite thin films with tunable magnetic performances by mechanical deformation

Integrating magnetic oxide thin films without restriction of substrates is crucial for their applications in electronic and spintronic devices. Here the water-soluble Sr3Al2O6 (SAO) layer is employed as the sacrificial layer to transfer the millimeter-size single-crystal Fe3O4 films from SrTiO3 (STO) to silicon and flexible PET substrates. Structural characterizations indicate that the transferred films have the same epitaxial quality with the as-grown films. The hysteresis loops measurements of flexible Fe3O4/PET samples show a deceasing magnetic anisotropy under both of convex and concave deformations. Such tunable magnetic anisotropy is confirmed by fitting the angular dependence of ferromagnetic resonance (FMR) fields. These results provide a damage-free way to fabricate single-crystal spinel ferrites films on the selected substrates for flexible spintronic devices.

Ferromagnetic resonance in a microtube

Ferromagnetic resonance fields in a microtube with various ratios of the inner and outer diameter of the tube β were studied using micromagnetic simulation. For β<0.15, the resonance field agrees with the prediction of the Kittel equation for an infinite ferromagnetic cylinder for both parallel and perpendicular orientation of the applied field to its axis. For β>0.15, the resonance field increases from the resonance field of the infinite cylinder and approaches the level of a film magnetized along the plane. This behavior only qualitatively agrees with the prediction made using the calculated demagnetizing factor in the ferromagnetic tube. For β>0.15 and the applied transverse field, a number of resonance peaks were observed for the microtube with the outer diameter of 500 nm, but for nanotubes with the diameters of 50 and 100 nm, a single peak was observed.

Direct Imaging of Resonant Phonon-Magnon Coupling

Direct detection of phonons is important for the investigation of information interconversion between the resonantly coupled magnons and phonons. Here we report resonant coupling of magnons and phonons, which can be directly visualized by using micro focused Brillouin light scattering in Ni/LiNbO3 hybrid heterostructures. The patterns of surface acoustic wave phonons, originating from the interference between the original wave {\psi}0(A_0,k) and reflected wave {\psi}1(A_1,-k), can be modulated by magnetic field due to the magnon-phonon coupling. By analyzing the information of phonons obtained from Brillouin spectroscopy, the properties of the magnon system (Ni film), e.g., ferromagnetic resonance field and resonance linewidth can be determined. The results provide spatially resolved information about phonon manipulation and detection in a coupled magnon-phonon system.

Ultraflexible and Malleable Fe/BaTiO3 Multiferroic Heterostructures for Functional Devices

AbstractThe high demand for flexible spintronics based on multiferroic heterostructures makes growing high‐quality flexible, functional oxides urgently, in which needs to be deposited on lattice‐matched substrates. In this paper, ultraflexible and malleable iron (Fe)/BaTiO3 (BTO) multiferroic heterostructures are demonstrated, showing a perfect crystallinity and hetero‐epitaxial growth. In terms of performance, they indicate good multiferroic properties and excellent bending tunability, as well as obvious magnetoelectric (ME) coupling effect. During the phase transformation from the rhombohedral phase to the orthorhombic phase of BTO layers in the heating process, a large ME coupling coefficient of 120 Oe °C−1 along the out‐of‐plane direction is obtained. This value keeps consistent in the phase‐field simulation of magnetic domain evolution, in which the biaxial compressive strain induced‐magnetoelastic anisotropy facilitates the magnetic easy axis of Fe layers to the [110] or [–1–10] direction. Besides, ultraflexible Fe/BTO heterostructures are found to have a 690 Oe ferromagnetic resonance (FMR) field shift along the out‐of‐plane direction under the flexible tuning (R = 5 mm). This work should pave a way toward flexible spintronic and functional devices with fast speed, portability, and low energy consumption.

Photovoltaic modulation of ferromagnetism within a FM metal/P-N junction Si heterostructure.

Obtaining small, fast, and energy-efficient spintronic devices requires a new way of manipulating spin states in an effective manner. Here, a prototype photovoltaic spintronic device with a p-n junction Si wafer is proposed which generates photo-induced electrons and changes the ferromagnetism by interfacial charge doping. A ferromagnetic resonance field change of 48.965 mT and 11.306 mT is achieved in Co and CoFeB thin films under sunlight illumination, respectively. The transient reflection (TR) analysis and the first principles calculation reveal the photovoltaic electrons that are doped into the magnetic layer and alter its Fermi level, correspondingly. This finding provides a new method of magnetism modulation and demonstrates a solar-driven spintronic device with abundant energy supply, which may further expand the landscape of spintronics research.

Modulation of spin dynamics across metal to insulator transitions in hybrid heterostructures

Novel functionalities can be achieved in nanostructured materials in proximity with other dissimilar materials. An interesting possibility along these composite heterostructures is offered by ferromagnets in proximity to materials that simultaneously undergo a metal-insulator transition (MIT) and structural phase transition (SPT). In this study, the temperature induced phase transition effect of VO2 films has been used to modulate the electron spin resonance (ESR) and spin switching behaviors of the perpendicular magnetized (Co/Pt)3 multilayers. With comparative investigation, a significant magnetization switching in the (Co/Pt)3 multilayers can be distinguished to be driven by the temperature induced SPT in the coupled VO2 films, which could lead to the switch of the magnetic easy axis from out-of-plane to in-plane direction. The SPT modulated magnetic anisotropy in the VO2 coupled magnetic multilayers can be further confirmed by the angular dependent ferromagnetic resonance (FMR) fields at different temperatures. This work explores the new-type strain modulation of spin dynamics with SPT in the hybrid heterostructures, which may benefit the development of next generation spintronics devices with novel functionalities.

Two-magnon frequency-pulling effect in ferromagnetic resonance

We report the experimental observation in thin films of the hybridization of the uniform ferromagnetic resonance mode with nonuniform magnons as a result of the two-magnon scattering mechanism, leading to a frequency-pulling effect on the ferromagnetic resonance. This effect, when not properly accounted for, leads to a discrepancy in the dependence of the ferromagnetic resonance field on frequency for different field orientations. The frequency-pulling effect is the complement of the broadening of the ferromagnetic resonance line shape by two-magnon scattering and can be calculated using the same parameters. By accounting for the two-magnon frequency shifts through these means, consistency is achieved in fitting data from in-plane and perpendicular-to-plane resonance conditions.

Controllable electric field tuning of anisotropic magnetic response of Ni/PMN-PT heterostructures

Epitaxial Ni films with various thicknesses were grown on (001)-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) substrates. Electric field tuning (E-tuning) of ferromagnetic resonance field (Hr) was utilized to investigate the magnetic response of Ni films along different film directions. Butterfly-like Hr vs E curves are shown when magnetic field is applied along film edge. While the combination of both loop-like and butterfly-like Hr vs E curves are observed for Ni film with thicknesses of 180 nm and 240 nm, and merely loop-like curves can be seen for film thicknesses of 330 nm and 510 nm, as magnetic field is applied along film diagonal. These interesting phenomena are assumed to be related to ferroelectric and ferroelastic domain switching in PMN-PT, film strain status, as well as magnetic anisotropy in Ni film. This work demonstrates the feasibility of control of anisotropic magnetic response via electric field in multiferroic heterostructure.

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.

Magnon-tuning non-volatile magnetic dynamics in a CoZr/PMN-PT structure

Magnon-tuning non-volatile magnetic dynamics is investigated in a CoZr/PMN-PT structure by measuring ferromagnetic resonance at room temperature. The electric-field control of ferromagnetic resonance shows loop-like behavior, which indicates non-volatile electric-field control of the magnetism. Further, fitting the curves of in-plane rotating angle versus ferromagnetic resonance field under different electric fields shows that the effective magnetic field changes in loop-like manner with the electric field. The resulting change in non-volatile saturation magnetization with electric field is consistent with that of a polarization electric field curve. A 1.04% change of saturation magnetization is obtained, which can be attributed to a magnon-driven magnetoelectric coupling at the CoZr/PMN-PT interface. This magnon-driven magnetoelectric coupling and its dynamic magnetic properties are significant for developing future magnetoelectric devices.

Photovoltaic Control of Ferromagnetism for Flexible Spintronics.

The demand for low-power flexible spintronics for sensing, communicating, and data processing applications boosts an intense search for novel ways of controlling magnetism. In this work, a photovoltaic controllable flexible spintronic device within a Kapton/Ta/Co/(PC71BM/PTB7-Th)/Pt heterostructure was demonstrated, and the magnetic anisotropy change of this flexible heterostructure as a function of the external light radiation and strain was quantitatively determined. 150 mW/cm2 white light illumination induced 489 Oe out-of-plane ferromagnetic resonance field modulation, which was attributed to the photogenerated electron doping in the cobalt film. The chemical contamination effect and the interfacial oxidation effect during the photovoltaic doping process were eliminated. Moreover, it was found that the working function of the thin-film electrodes were different from the bulk values via an ultraviolet photoelectron spectroscopy test. Our results on flexible photovoltaic spintronics systems will invigorate the research toward the development of solar-driven energy-efficient spintronics.

The microwave magnetism of epitaxy LiFe5O8 thin film modulated by thickness

Spinel lithium ferrite LiFe5O8 (LFO) has attracted robust research interests due to their potential applications in isolators, circulators, and phase shifters. In this work, a series of LFO thin film with various thickness were fabricated on SrTiO3 (STO) single-crystalline substrates by pulsed laser deposition technology. We systematically investigated the influences of the thickness of LFO thin film on the crystal structure and magnetic properties. The in-plane lattice parameter a and in-plane lattice parameter c were modulated by controlling the thickness of LFO thin film, which was confirmed using reciprocal space mappings (RSMs) technology. Furthermore, the microwave magnetism of LFO thin film with various thickness were studied systematically by ferromagnetic resonance (FMR) measurement. Moreover, with increasing the thickness of LFO thin film from 50 to 180 nm, the difference of the ferromagnetic resonance field between easy- and hard-magnetization axis can be enhanced and reach to 330 Oe. These results illustrate that dynamic magnetic properties can be controlled by tuning the thickness of LFO thin film. Our work provides an effective method to tailor the lattice parameter and modify the magnetic properties of the LFO thin film and contributes to further design high-frequency functional device.

Enhanced electrical switching of magnetism in the artificial multiferroic CoFeB/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure

Multiferroic heterostructure CoFeB/Pb(Mg1/3Nb2/3)O3–PbTiO3 is prepared by depositing CoFeB films on Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal through direct current magnetron sputtering. The electric field induced magnetism change of CoFeB film was studied by magneto-optical Kerr effect measurement. The magnetic hard/easy axis change was investigated under direct current electric field. Alternative current voltage magneto-optical Kerr effect test indicates the different magnetoelectric mechanism with the change of film thickness. The microwave frequency tunability was observed under the electric field and the tunable ferromagnetic resonance field reaches 190 Oe. Our study provides great opportunities for the application of electric-field tunable information storage devices.

Discussion of strong pinning effect via nonuniform PSSW mode in Fe/NiFe/Fe multi-layer films with different Fe film thicknesses

Multilayer films with high saturation magnetization and low ferromagnetic resonance linewidth have great potential for various applications in the era of high frequency and miniaturization. In this study, Fe (t nm)/Ni81Fe19 (50 nm)/Fe (t nm) multilayer films were fabricated using electron beam evaporation, and the microstructure, saturation magnetization, coercivity, ferromagnetic resonance (FMR) linewidth and perpendicular standing spin-wave (PSSW) mode are discussed in detail. With increasing Fe film thickness, the saturation magnetization of the multilayer films increased from 10,547 to 14,494 Gs, becoming closer to the theoretical value, and the ferromagnetic resonance linewidth showed an overall increasing trend. It is worth noting that a strong pinning effect has been found via the appearance of the PSSW mode in the FMR spectrum, when the thickness of Fe reaches 4 nm. As the thickness of the Fe film increased from 4 to 15 nm, the perpendicular standing spin-wave field (Hp) increased from 133 to 379 Oe, and the perpendicular standing spin-wave linewidth (ΔHp) increased from 68 to 148 Oe. Remarkably, with 8 nm thick Fe film, the multilayer films achieved excellent comprehensive performances with high saturation magnetization (4πMs, 13,525 Gs), a low in-plane ferromagnetic resonance field (Hr, 725 Oe), and a low FMR linewidth (ΔH, 84.24 Oe).

Sunlight Control of Interfacial Magnetism for Solar Driven Spintronic Applications.

The inexorable trend of next generation spintronics is to develop smaller, lighter, faster, and more energy efficient devices. Ultimately, spintronics driven by free energy, for example, solar power, is imperative. Here, a prototype photovoltaic spintronic device with an optical‐magneto‐electric tricoupled photovoltaic/magnetic thin film heterojunction, where magnetism can be manipulated directly by sunlight via interfacial effect, is proposed. The magnetic anisotropy is reduced evidenced by the out‐of‐plane ferromagnetic resonance (FMR) field change of 640.26 Oe under 150 mW cm−2 illumination via in situ electron spin resonance (ESR) method. The transient absorption analysis and the first‐principles calculation reveal that the photovoltaic electrons doping in the cobalt film alter the band filling of this ferromagnetic film. The findings provide a new path of electron doping control magnetism and demonstrate an optical‐magnetic dual controllable logical switch with limited energy supply, which may further transform the landscape of spintronics research.

Integration of Both Invariable and Tunable Microwave Magnetisms in a Single Flexible La0.67Sr0.33MnO3 Thin Film.

High-quality flexible magnetic oxide thin films have promoted a wide range of potential applications in spintronic devices due to their unique physical properties. To obtain the optimized microwave magnetism for future all-oxide-based spintronic applications, high-quality oxide materials with excellent epitaxial quality as well as specific bending properties related to ferromagnetic resonance are high in demand. Here, (001)-oriented La0.67Sr0.33MnO3 epitaxial thin films with different thicknesses have been grown and subsequently transferred onto flexible poly(dimethylsiloxane) substrates. The microwave magnetisms of these film samples have been investigated under various bending states. Under bending, the ferromagnetic resonance lineshape of the film gradually transits from a single mode to a superposition of multimodes, possibly because of the uneven distribution of magnetization in the bending film at X-band. This phenomenon is more apparent when the direction of the applied magnetic field goes close to the out-of-plane of the film. Hence, an integration of invariable and continuous tuning of ferromagnetic resonance field under various mechanical bending can be achieved in one same sample by just tuning the direction of the applied magnetic field, which reveals that the flexible La0.67Sr0.33MnO3 thin films have huge potential in the applications in future flexible multifunctional devices.

Low-Voltage-Manipulating Spin Dynamics of Flexible Fe3O4 Films through Ionic Gel Gating for Wearable Devices.

Mechanical flexible electronic/spintronic devices have shown enormous application potential to impact our daily life. Here, an in situ low-voltage-controlled flexible field-effect transistor structure was exploited, which consists of a support layer (mica), functional layer (Fe3O4), and control layer (ionic gel). By applying a low voltage (1.5 V) on the ionic gel, the spin-dynamic properties of the function layer were manipulated and a reversible, nonvolatile 345 Oe ferromagnetic resonance field ( Hr) shift was achieved, which corresponds to a large magnetoelectric (ME) coefficient of 230 Oe/V. In addition, a reversible 126 Oe Hr shift (84 Oe/V) was obtained when the layers were bent at curvature radius r = 15 mm. The ME tunability could be attributed to the E-field induced ionic transformation between Fe2+ and Fe3+ at the interface via electrostatic induction. This sandwich structure shows an excellent and effective ionic gel gating system and paves the way for low-voltage-tunable, nonvolatile, and flexible spintronic devices such as memory devices, sensors, and logical devices.

Ferromagnetic resonance property in the magnetic heterostructure with Fe nanowire arrays and Fe25Ni75 film

Abstract The magnetic heterostructures, consisting of Fe nanowire arrays (FNWs) and Fe25Ni75 film, are prepared by combining electrochemical deposition and RF magnetron sputtering. The ferromagnetic resonance (FMR) property in the magnetic heterostructures is investigated by using frequency sweep mode and field sweep mode. The results of hysteresis loops and permeability spectra indicate that the FNWs could destroy the stripe domain structure in Fe25Ni75 film. The resonance absorption near the FMR field is excited in the heterostructures, which can be attributed to the spin non-uniform precession namely spin waves resonance excitation.

Temperature dependent magnetism modulated by electric fields at the NiFe/PZT interface

Abstract The temperature dependences of magnetization and surface magnetic anisotropy are reported by reversing electric fields at the interface of a Ni80Fe20/PbZr0.44Ti0.56O3 multiferroic heterostructure. Both the in-plane magnetization variation and the isotropic ferromagnetic resonance field suggest that the magnetoelectric coupling effect arises from the interfacial accumulation or depletion of spin-polarized electrons, rather than the strain. As the temperature decreases, the ferromagnetic resonance field shifts left and the surface magnetic anisotropy deduced from the shift of ferromagnetic resonance field increases faster than the saturation magnetization. The strong temperature dependences of magnetization and surface magnetic anisotropy are related to the changes in the spin-polarized electron density due to the thermal motion.