In-plane Uniaxial Magnetic Anisotropy Research Articles

Enhanced magnetic anisotropy and its thermal stability in obliquely deposited Co-Film on the nanopatterned substrate

The deliberate manipulation of magnetic anisotropy through controlled adjustments to surface and interface morphology has become important due to its potential applications in spintronics and magnetic memory devices. In the present work, oblique angle deposition (OAD) at 65° to the surface normal on a rippled substrate, keeping nanopatterns on the SiO2 substrate perpendicular to the OAD projection, has been used to induce in-plane uniaxial magnetic anisotropy (UMA) and its thermal stability in cobalt (Co) thin film. Prior to film preparation, the patterned substrate of wavelength 68 ± 4 nm and amplitude 3.4 ± 0.2 nm was prepared separately using a low-energy ion beam erosion (IBE) process. Grazing incidence small-angle X-ray scattering (GISAXS) and magneto-optical Kerr effect (MOKE) techniques have been used for film characterization. While GISAXS provided information about film structure and morphology, MOKE provided information about magnetic properties, thus making it possible to correlate the temperature-dependent evolution of morphology with that of UMA in the film. A clear anisotropy in the growth of Co film is found to result in strong UMA. Unlike previous studies, which typically observe a reduction in UMA strength with thermal annealing, the present work demonstrates a 31 % increase in UMA strength after annealing up to 200 °C, underscoring the importance of oblique angle deposition on nano-rippled substrates for achieving high UMA and ensuring its thermal stability up to moderate temperatures. The appearance of large UMA and its unusual temperature dependence is understood in terms of the shadowing effects and column coalescence, resulting in more robust shape anisotropy. This work provides insights into morphological anisotropy, elucidating the interplay of shadowing effects, shape anisotropy, and dipolar interactions within interacting column and ripple structures. This method gives rise to morphology-induced anisotropy, which can also be applied to other ferromagnetic films to enhance the magnetic anisotropy and ensure thermal stability.

Effects of Buffer and Capping Layers on Thermal Stability of CoFeB/MgO Frames at Various Temperatures

The utilization of CoFeB thin films in spintronic devices has attracted significant attention due to their exceptional magnetic properties, which include high saturation magnetization and spin polarization. However, the effect of ambient temperature on the magnetic properties of CoFeB/MgO frames, particularly those with different buffer and capping layers, remains unexplored. Therefore, in this study, the magnetostatic and dynamic properties of CoFeB/MgO frames were investigated at various temperatures. Using vibrating sample magnetometry and ferromagnetic resonance spectroscopy, changes in key parameters such as saturation magnetization, the Gilbert damping constant, magnetic anisotropy field, in-plane uniaxial magnetic anisotropy energy, and thermal stability factor were investigated. Furthermore, the thermal stabilities of CoFeB/MgO frames with Ta buffer and capping layers were compared with those of CoFeB/MgO frames with W buffer and capping layers by examining the changes in the key parameters at various temperatures. These results reveal that the thermal stability of the latter surpassed that of the former. This study provides significant insights for the development of thermally robust spintronic devices capable of operating above room temperature.

Single-crystalline YIG flakes with uniaxial in-plane anisotropy and diverse crystallographic orientations

We study sub-micron Y3Fe5O12 (YIG) flakes that we produce via mechanical cleaving and exfoliation of YIG single crystals. By characterizing their structural and magnetic properties, we find that these YIG flakes have surfaces oriented along unusual crystallographic axes and uniaxial in-plane magnetic anisotropy due to their shape, both of which are not commonly available in YIG thin films. These physical properties, combined with the possibility of picking up the YIG flakes and stacking them onto flakes of other van der Waals materials or pre-patterned electrodes or waveguides, open unexplored possibilities for magnonics and for the realization of novel YIG-based heterostructures and spintronic devices.

Achieving in-plane biaxial magnetic anisotropy of permalloy films by localized magnetoelastic coupling

Magnetic films with in-plane magnetic anisotropy have been extensively applied in the field of magnetoelectronic devices. Here, we report a control method for the in-plane magnetic anisotropy of Ni80Fe20 films by localized magnetoelastic coupling. Nanotrenches are patterned on Ni80Fe20/polymethyl methacrylate bilayers, and the Young’s modulus mismatch between micro-patterned magnetic/polymer layers directionally releases the local stress. Due to magnetoelastic coupling, the directed tension distribution can rearrange the stripe domain along the patterned nanotrenches and induce the in-plane uniaxial magnetic anisotropy of the Ni80Fe20 films. Using hierarchically patterned tension distributions with 2D nanotrench arrays, in-plane biaxial magnetic anisotropy can be arbitrarily designable in Ni80Fe20 films.

Regulation of static and dynamic magnetic properties of amorphous FeCoZr composition gradient films by Zr doping

A series of amorphous FeCoZr composition gradient monolayer films with varying Zr contents was prepared on the Si(100) substrate using RF magnetron sputtering. The effects of the Zr sputtering power PZr on the static and dynamic magnetic properties of FeCoZr films were systematically investigated. The results demonstrate that the introduction of the Zr element as a composition gradient into FeCo films not only improves the soft magnetic properties of the films but also enhances their in-plane uniaxial magnetic anisotropy. In particular, the doping of Zr elements leads to the destruction of FeCo lattice, inducing a transformation of the films from polycrystalline to amorphous state, resulting in a significant decrease in coercivity (Hc reduced by 82%) and surface roughness (Ra reduced by 78%). In addition, as PZr increases from 30 to 70 W, the anisotropy fields Hk of the films increase from 128 to 340 Oe, and the resonance frequency fr increases from 4.24 to 5.23 GHz. By fitting the permeability spectrum using the LLG equation, it is found that FeCoZr composition gradient films exhibit a lower damping coefficient α of around 0.011–0.014, indicating the reduction of energy loss during magnetization dynamics. These findings highlight the potential applications of FeCoZr composition gradient films in the field of high-frequency microwaves.

Twisted Integration of Complex Oxide Magnetoelectric Heterostructures via Water-Etching and Transfer Process

HighlightsThe (001)-oriented ferromagnetic La0.67Sr0.33MnO3 films are stuck onto the (011)-oriented ferroelectric single-crystal 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate with 0° and 45° twist angle.By applying a 7.2 kV cm−1 electric field, the coexistence of uniaxial and fourfold in-plane magnetic anisotropy is observed in 45° Sample, while a typical uniaxial anisotropy is found in 0° Sample.Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering. In recent years, lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations. Moreover, twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures. A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process, which could provide some insight in to the physical phenomena. In this work, the La0.67Sr0.33MnO3 (001)/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (011) (LSMO/PMN-PT) heterostructures with 45º and 0º twist angles were assembled via water-etching and transfer process. The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO < 110 >. A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO [110] easy axis is observed for the 45° Sample by applying a 7.2 kV cm−1 electrical field, significantly different from a uniaxial anisotropy with LSMO [100] easy axis for the 0° Sample. The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45° twist angle causes different lattice distortion of LSMO, thereby enhancing both the fourfold and uniaxial anisotropy. This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures.

Ultrahigh in-plane uniaxial magnetic anisotropy of amorphous FeCoHf composition gradient films

Amorphous FeCoHf films with a Hf composition gradient were prepared at room temperature. The composition gradient sputtering technique was used to control the composition gradient of the doped element Hf by changing the deposition power of Hf. Interestingly, in the as-deposited FeCoHf films, an in-plane uniaxial magnetic anisotropy field of up to 640 Oe was achieved, and the resonance frequency was 6.5 GHz. The large anisotropy field can be attributed to the high sensitivity of the amorphous FeCoHf films to the composition gradient. The ultrahigh anisotropy exhibited by FeCoHf films at room temperature holds significant technological potential for various applications.

60∘ and 120∘ domain walls in epitaxial BaTiO3 (111)/Co multiferroic heterostructures

We report on domain pattern transfer from a ferroelectric ${\mathrm{BaTiO}}_{3}$ substrate with a (111) orientation of the surface to an epitaxial Co film grown on a Pd buffer layer. Spatially modulated interfacial strain transfer from ferroelectric/ferroelastic domains and inverse magnetostriction in the ferromagnetic film induce stripe regions with a modulation of the in-plane uniaxial magnetic anisotropy direction. Using spin-polarized low-energy electron microscopy, we observe the formation of two distinct anisotropy configurations between stripe regions, leading to angles of ${60}^{\ensuremath{\circ}}$ or ${120}^{\ensuremath{\circ}}$ between the magnetizations of adjacent domains. Moreover, through application of a magnetic field parallel or perpendicular to these stripes, head-to-head or head-to-tail magnetization configurations are initialized. This results in four distinct magnetic domain-wall types associated with different energies and domain widths, which, in turn, affects whether domain pattern transfer can be achieved.

Competition between exchange and magnetostatic energies in domain pattern transfer from BaTiO3 (111) to a Ni thin film

We use spin-polarized low-energy electron microscopy to investigate domain pattern transfer in a multiferroic heterostructure consisting of a (111)-oriented ${\mathrm{BaTiO}}_{3}$ substrate and an epitaxial Ni film. After in situ thick-film deposition and annealing through the ferroelectric phase transition, interfacial strain transfer from ferroelastic domains in the substrate and inverse magnetostriction in the magnetic thick film introduce a uniaxial in-plane magnetic anisotropy that rotates by ${60}^{\ensuremath{\circ}}$ between alternating stripe regions. We show that two types of magnetic domain wall can be initialized in principle. Combining experimental results with micromagnetic simulations, we show that a competition between the exchange and magnetostatic energies in these domain walls has a strong influence on the magnetic domain configuration.

Magnetic and structural properties of sputtered thick Co2FeSi alloy films

We investigate magnetic and structural properties of the sputtered thick Co2FeSi (CFS) alloy films. X-ray diffraction measurements show CFS alloy film changes from amorphous to disordered A2 structures after annealing, which leads to pronounced increase in saturation magnetization. For the as-deposited films in-plane uniaxial magnetic anisotropy is determined to be in the range of 103–104 erg/cm3, showing strongly dependent to film thickness. After annealing a fourfold cubic magnetic anisotropy is witnessed. Structural ordering is observed to improve with increasing film thickness. Similiar trend of the magnetic anisotropy with sputtering power is witnessed, which can be explained by equivalent annealing effect of the high-power sputtering. Our results show that magnetic anisotropy properties of the CFS alloy films are strongly dependent to film thickness and structural ordering, tuned by anealing tempeature and sputtering power. These findings may be helpful for designing Co2FeSi-based spintronic devices.

Micromorphology and uniaxial magnetic anisotropy of oblique-sputtered Ni80Fe20 films on periodically rippled Al2O3 substrates

Ni80Fe20 (NiFe) films were deposited on periodically rippled Al2O3 substrates by two different template oblique angle deposition (OAD) processes at various oblique deposition angles α (0° ≤ α ≤ 60°). The disparate in-plane uniaxial magnetic anisotropy (UMA) caused by the two template deposition processes of films was revealed by magneto-optical Kerr effect (MOKE) loops and ferromagnetic resonance (FMR) measurements. The analysis of Transmission electron microscopy images indicated that this was related to the different micromorphology of the films due to the two template deposition processes. The angle between substrates’ ripple direction and the material flow incident direction would strongly influence the micromorphology and the induced in-plane UMA field of films. The values of the UMA field of these films can be much larger than those of the films oblique deposited on the plane Al2O3 substrates at the same α by choosing the template deposition direction. The results would help further modulate the UMA of magnetic films deposited on rippled substrates, which would be beneficial for the applications of these films in spintronic, magnetic memory and magnetic microwave devices.

In-plane magnetic anisotropy and magnetization reversal in phase-separated (La0.5Pr0.5)0.625Ca0.375MnO3 thin films

The dynamics and interaction of different electronic phases near the metal-to-insulator transition of the phase-separated ${({\mathrm{La}}_{0.5}{\mathrm{Pr}}_{0.5})}_{0.625}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$ (LPCMO) thin film grown on NGO substrate was studied using the first-order reversal curves (FORC) diagram method for electric transport measurements. The in-plane angle-dependent remanence and coercivity field in the region of the ferromagnet metallic phase was measured using the macroscopic magnetization technique. These measurements suggest an in-plane uniaxial magnetic anisotropy for the film with a uniaxial anisotropic constant (Ku) of $\ensuremath{\sim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}\mathrm{erg}/\mathrm{c}{\mathrm{m}}^{3}$ at 20 K. The angle dependence of the coercivity is best described by 1/cos\ensuremath{\theta} dependence indicating that the magnetization reversal occurs mainly through the depinning of the domain wall, a signature of nucleation and propagation mechanism. The correlation of FORC measurements, resistance relaxation, and macroscopic magnetic measurements indicate a fast reversal of electronic and magnetic phases towards the denser phase region and strong interaction of different phases for the LPCMO system.

Enhancing the limit of uniaxial magnetic anisotropy induced by ion beam erosion

Artificial tailoring of magnetic anisotropy by manipulating interfacial morphology and film structure is of fundamental interest from an application point of view in spintronic and magnetic memory devices. This Letter reports an approach to engineer and enhance the strength of oblique incidence ion beam erosion (IBE)-induced in-plane uniaxial magnetic anisotropy (UMA) by simultaneous modification of film morphology and film texture. Cobalt film and Si substrate have been taken as a model system to meet this objective. Unlike conventional thin film deposition on ripple patterned substrate or post-growth IBE of film, we direct our effort to the sequential deposition and subsequent IBE of the film. Detailed in situ investigation shows that the film grows in a textured polycrystalline state with the formation of nanometric surface ripples. The film also exhibits pronounced UMA with an easy axis oriented parallel to the surface ripple direction. Remarkably, the induced UMA is about one order of magnitude larger than the IBE-induced UMA reported earlier. The capability of imposing in-plane crystallographic texture throughout the film layer gives rise to magneto-crystalline anisotropy along with the shape anisotropy of nanometric surface ripples, which enhances the strength of the UMA and illustrates the universal applicability of the present method.

Role of interfacial nickel silicides in shaping magnetic anisotropy in nickel films grown on Silicon substrates

Using different experimental techniques such as X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy and magneto-optical Kerr effect (MOKE) microscopy, the structural and magnetic properties of Ni films grown on Si substrates are investigated. Various Ni-silicide phases are found to be formed at the Ni–Si interface as a function of depth following the sequence Ni-Ni2Si-NiSi-NiSi2 from the nickel to silicon side. This has been explained in terms of the effective heat of formation and inter-diffusion of the elements at the interface. In-plane magnetic anisotropy of the system is investigated by measuring in-plane magnetization using MOKE microscopy. The film exhibits an uniaxial in-plane magnetic anisotropy. An anomalous behavior, i.e., the collapse of the hard axis, has also been observed. This anomaly has been explained in terms of the creation of V-state domains during the magnetization reversal process at the hard axis. Interestingly, in-plane magnetic anisotropy could not be found in a Ni film grown with a Pt buffer layer on the Si substrate. Ni-silicide phases could not be detected in this system. This may suggests that the formation of silicides and diffusion at the interface causes the atypical magnetic anisotropy in Ni–Si sample.

Tunable magnon-magnon coupling mediated by in-plane magnetic anisotropy in synthetic antiferromagnets

The magnon–magnon coupling is the key issue to exchange information in hybrid magnonic systems. We investigate the magnon–magnon coupling in a synthetic antiferromagnet (SAF) system with the presence of an in-plane uniaxial magnetic anisotropy via micromagnetic simulations. The magnon–magnon coupling arises, and its strength is field-direction dependent. The maximum magnon–magnon coupling occurs when the in-plane magnetic field along 45° deviates from the easy axis. The magnon–magnon coupling can be regulated by the in-plane magnetic anisotropy field. The dynamical phase between two magnetic layers is neither 0° nor 180°, which indicates the magnon in a hybrid mode. This study provides a simple method for a tunable magnon–magnon coupling in SAFs to realize a practical hybrid quantum system based on magnonics.

Magnetocaloric and Giant Magnetoresistance Effects in La-Ba-Mn-Ti-O Epitaxial Thin Films: Influence of Phase Transition and Magnetic Anisotropy.

Magnetic perovskite films have promising properties for use in energy-efficient spintronic devices and magnetic refrigeration. Here, an epitaxial ferromagnetic La0.67Ba0.33Mn0.95Ti0.05O3 (LBMTO-5) thin film was grown on SrTiO3(001) single crystal substrate by pulsed laser deposition. High-resolution X-ray diffraction proved the high crystallinity of the film with tetragonal symmetry. The magnetic, magnetocaloric and magnetoresistance properties at different directions of the applied magnetic field with respect to the ab plane of the film were investigated. An in-plane uni-axial magnetic anisotropy was evidenced. The LBMTO-5 epilayer exhibits a second-order ferromagnetic-paramagnetic phase transition around 234 K together with a metal-semiconductor transition close to this Curie temperature (TC). The magnetic entropy variation under 5 T induction of a magnetic field applied parallel to the film surface reaches a maximum of 17.27 mJ/cm3 K. The relative cooling power is 1400 mJ/cm3 K (53% of the reference value reported for bulk Gd) for the same applied magnetic field. Giant magnetoresistance of about 82% under 5 T is obtained at a temperature close to TC. Defined as the difference between specific resistivity obtained under 5 T with the current flowing along the magnetic easy axis and the magnetic field oriented transversally to the current, parallel and perpendicular to the sample plane, respectively, the in-plane magneto-resistance anisotropy in 5 T is about 9% near the TC.

Uniaxial in-plane magnetic anisotropy mechanism in Ni, Fe, and Ni-Fe alloy films deposited on single crystal Y-cut 128° LiNbO3 using magnetron sputtering

We investigated the mechanism of induced in-plane uniaxial magnetic anisotropy (Ku) in Nickel (Ni), Iron (Fe), and Ni-Fe alloy films deposited in situ on a single-crystal 128° Y-cut LiNbO3 (LNO) substrate at various substrate heating temperatures (Th) in the range 30–400 °C through radio frequency magnetron sputtering or co-sputtering. The results show that the Ku values for the Ni, Fe, and Ni-Fe alloy films are induced in the (01.2) or (21¯.0) planes of the LNO substrate. The highest value of Ku for the Ni films was observed at Th = 200 °C, which is owing to the increased orientation of the fcc Ni (311) plane. The Ni film with thickness t ∼ 20 nm deposited on the LNO substrate at Th = 200 °C possesses the highest value of Ku. Density functional theory calculations show that the magnetic anisotropic energy on the fcc Ni (311) plane differs depending on the magnetization direction in the in-plane direction in the model. Meanwhile, the value of Ku for the Fe films decreases with an increase in the value of Th because the films with higher Th are polycrystalline and have an oxide layer. The composition dependence of Ku for Ni-Fe alloy films at Th = 30 °C shows a trend similar to the crystal magnetic anisotropy for bulk Ni-Fe alloy. The induced Ku on LNO is attributed to the magnetostriction effect with the change in the crystal orientation of the ferromagnetic metal owing to a strain from the LNO substrate through the thermal expansion during sputtering. These results indicate the origin of the induced Ku in the Ni and Fe based metallic material films deposited on the LNO substrate.

The Effect of Obliquely Sputtered Cu Underlayers with Different Thicknesses on the Magnetic Properties of 50 nm Ni80Fe20 Thin Films

The magnetic properties of 50 nm Ni80Fe20 deposited on Cu underlayers with different thicknesses by obliquely sputtering were studied. It was found that the in-plane uniaxial magnetic anisotropy (IPUMA) of the Ni80Fe20 film can be induced by the obliquely sputtered Cu underlayer deposited under the NiFe layer. The IPUMA field of NiFe film varies between 20 Oe and 40 Oe when the thickness of Cu underlayer varies from 5 nm to 50 nm. The permeability spectrum results show that the damping factor increases with increasing Cu underlayer thickness. This indicates that changing the thickness of the Cu underlayer of obliquely sputtering is an effective method to adjust the damping factor in the dynamic magnetization process of Ni80Fe20 thin films.

Strong uniaxial magnetic anisotropy in Fe3Si thin films

Thin Fe3Si films grown on Si/SiO2 substrates by ion-beam and pulsed laser deposition possess soft ferromagnetic behavior and strong in-plane uniaxial magnetic anisotropy. The material of the capping layer and deposition of the buffer layer do not affect the presence and character of obtained anisotropy. The structural studies showed that Fe3Si film deposited on amorphous SiO2 layer is polycrystalline while the same layer grown on polycrystalline Ta buffer layer is amorphous. It has also been found that uniaxial anisotropy is similar for amorphous and crystalline DO3 Fe3Si films. Magnetic properties yield a magnetization saturation of both amorphous and crystalline films as 1050 emu/cm3 at room temperature and coercive field not exceeding 5 Oe. The origin of such an anomalous behavior were discussed in terms of deposition technique features and parameters, substrate and capping layer type and resulting film parameters.

Magnetic Properties of FeNi Films Prepared by Oblique Deposition at Different Growth Conditions

FeNi films were prepared by oblique deposition onto glass substrate using magnetron sputtering deposition technique. The deposition was carried out on a rotating or nonrotating substrate with or without a constant magnetic field applied parallel to the substrate plane. The magnetic properties of the samples were measured by a magneto-optical Kerr effect at room temperature. All films had in-plane uniaxial magnetic anisotropy. The presence of in-plane magnetic anisotropy was also confirmed by the features of the domain structure. The main factor determining the orientation of the induced anisotropy axis of films was the magnetic field applied during deposition.