Magnetic Anisotropy Of Fe Films Research Articles

Transfer of magnetic anisotropy in epitaxial Co/NiO/Fe trilayers

The magnetic properties of Co(10 Å)/NiO(40 Å)/Fe trilayer epitaxially grown on W(110) substrate were investigated with use of x-ray magnetic linear dichroism (XMLD) and x-ray magnetic circular dichroism (XMCD). We showed that magnetic anisotropy of Fe film that can be controlled by a thickness-driven spin reorientation transition is transferred via interfacial exchange coupling not only to NiO layer but further to ferromagnetic Co overlayer as well. Similarly, a temperature driven spin reorientation of Fe sublayer induces a reorientation of NiO spin orientation and simultaneous switching of the Co magnetization direction. Finally, by element specific XMCD and XMLD magnetic hysteresis loop measurements we proved that external magnetic field driven reorientation of Fe and Co magnetizations as well as NiO Néel vector are strictly correlated and magnetic anisotropy fields of Fe and Co sublayers are identical despite the different crystal structures.

Recovering in-plane six-fold magnetic symmetry of epitaxial Fe films by N<sup>+</sup> implantation

In order to study the effect of ion implantation on the in-plane magnetic anisotropy of epitaxial magnetic films, a 3-nm Al buffer layer is epitaxially grown on an Si (111) substrate with a miscut angle, and then 25-nm Fe is grown on the buffer layer. High-resolution X-ray diffraction reveals that the epitaxial Fe film has a (111)-oriented bcc structure. The epitaxial Fe films are implanted by 10 keV N<sup>+</sup> ions with dose up to 5 × 10<sup>16</sup> ions/cm<sup>2</sup>. The change and mechanism of the in-plane magnetic anisotropy of the epitaxial Fe film are studied systematically. It is found that the in-plane magnetic anisotropy of the epitaxial Fe film is gradually changed from two-fold to six-fold symmetry with the increase of N<sup>+</sup> implantation dose. It is confirmed by transmission electron microscopy and etching experiments that ion implantation changes the surface and interface state of Fe film. This result is consistent with the result from the SRIM software simulation. The in-plane magnetic uniaxial anisotropy of epitaxial Fe film comes from atomic steps at the surface and the interface of the Fe film. These steps result from Si (111) substrate with a miscut angle. Ion implantation has effects on sputtering and atomic diffusion. The sputtering effect causes the step at the surface of the Fe film to be erased, and the diffusion of the atom leads the step at the interface of the Fe film to disappear. The in-plane uniaxial anisotropy induced by the atomic step is weakened, and the magnetocrystalline anisotropy induced by the Fe (111) plane is dominant. Therefore, the epitaxial Fe film exhibits Fe (111) plane induced six-fold magnetic symmetry after high-dose N<sup>+</sup> implantation. This work indicates that the in-plane magnetic anisotropy of Fe films epitaxially grown on Si (111) substrate with miscut angle can be modified and precisely controlled by ion implantation. This work may be of practical significance for improving the density of in-plane magnetic recording material.

Magnetic anisotropy of crystalline Fe films grown on (001) GaAs substrates using Ge buffer layers

Magnetic anisotropy of Fe films grown on (001) GaAs substrates using Ge buffer layers were investigated by planar Hall effect measurements. In addition to phenomena arising from dominant cubic symmetry of the Fe specimen, the study of angular dependence of magnetization reversal revealed breaking of this symmetry in the form of systematic asymmetric shifts of magnetic hysteresis loops around the <110 > crystallographic directions. We ascribe such symmetry breaking to an admixture of uniaxial anisotropy associated with the [100] direction in the Fe film. To determine the parameters associated with this uniaxial anisotropy, we quantitatively analyze the asymmetric shifts of the hysteresis loop centers from the <110 > directions. Even though the value of these parameters turns out to be relatively small compared to that of the cubic anisotropy (by about two orders of magnitude), they survive up to room temperature.

Buffer layer dependence of magnetic anisotropy in Fe films grown GaAs substrate

The effect of buffer layer on the magnetic anisotropy of Fe film has been investigated by using the planar Hall effect measurement. The Fe films were grown on four different buffer layers, such as GaAs, ZnSe, ZnTe, and Ge, by molecular beam epitaxy. The field and angle dependent planar Hall effect measurements revealed the presence of two types of magnetic anisotropies, i.e., cubic crystalline anisotropy along the 〈100〉 directions and uniaxial anisotropy along the 〈110〉 crystallographic directions, in all four Fe films investigated in the study. However, the relative strength of the two types of anisotropies varies significantly depending on the type of buffer layer. Specially, in the Fe film grown on the Ge buffer layer, the uniaxial anisotropy almost disappeared and the entire magnetic anisotropy was dominated by cubic anisotropy with a four-fold symmetry. This suggests that the growth of Fe film on the Ge surface is different from its growth on other surfaces such as GaAs, ZnSe, and ZnTe buffers, where the asymmetric reconstruction process of anions (i.e., As, Se, or Te) is present at the surface.

Voltage control of magnetic anisotropy in Fe films with quantum well states

The influence of a gate voltage on magnetic anisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magnetic anisotropy due to quantum well states (QWS) confined in the Fe film are observed and shown to persist up to room temperature at low Fe thicknesses. By systematically examining the voltage and thickness dependence of the magnetic hysteresis loop characteristics, we identify two distinct effects by which an applied voltage modifies the magnetic anisotropy. The first effect is due to voltage-induced changes to interfacial perpendicular magnetic anisotropy which, due to the vicinal geometry, leads to changes in the effective in-plane uniaxial magnetic anisotropy. A second effect is observed at lower film thicknesses and shows nonmonotonic voltage-induced effects on magnetic anisotropy. This nonmonotonic behavior coincides with the onset of significant QWS-induced effects on magnetic anisotropy and suggests a link between QWS- and voltage-induced anisotropy changes.

Tuning the lattice and magnetic anisotropy of Fe thin films

Fe (001) thin films with different crystal lattice were epitaxially grown on single crystal MgO substrates under the various sputtering pressures. It is found in this paper that the tetragonality and magnetic anisotropy of Fe thin film is tuned by varying the working sputtering pressures. The tunability of the crystal lattice and the magnetic anisotropy of Fe films were characterized by X-ray reflectivity, X-ray diffraction and vibrating sample magnetometer. The tunable structure and magnetic properties of Fe thin films may attribute to the rearrangement of Fe atoms on MgO substrate induced by controlling the atomic kinetic energy under different sputtering pressure.

Magnetic anisotropy in Fe films deposited on SiO2/Si(001) and Si(001) substrates

The magnetic anisotropy of 10nm iron films deposited in an ultra high vacuum on the Si(001) surface and on the Si(001) over caped by 1.5nm layer of SiO2 was investigated. There is in-plane uniaxial magnetic anisotropy caused by oblique sputtering in the Fe films on a SiO2 buffer layer. The easy magnetization axis is always normal to the atomic flux direction but the value of the anisotropy field is different depending on the axial angle among sputtering direction and the substrate crystallographic axes. It is argued that the uniaxial magnetic anisotropy results from elongated surface roughness formation during film deposition. Several easy magnetization axes are found in Fe/Si(001) film without the SiO2 buffer layer. The mutual orientation of the main easy axes and Si crystallographic axes indicates that there is epitaxial growth of Fe/Si(001) film with the following orientation relative to the substrate: Fe[100] ∥Si[110]. The anisotropy energy of Fe/Si(001) film is estimated by simulation of angle dependence of remnant magnetization mr as the sum of the mr angle plot from uniaxial anisotropy (induced by oblique deposition) and the polar plot from biaxial magnetocrystalline anisotropy.

Magnetic anisotropy in Fe films epitaxied by thermal deposition and pulse laser deposition on GaAs(001)

The in-plane magnetic anisotropy of Fe films fabricated with thermal deposition (TD) and pulse laser deposition (PLD) techniques on GaAs(001) substrate was studied quantitatively. The volume anisotropy in TD Fe film is attributed to the constant strain anisotropy, supported by reflection high-energy electron diffraction analysis. The PLD growth was found to deeply influence the interface anisotropy at Fe/GaAs interface even through a 30 ML Fe TD underlayer. The volume anisotropy was found to exist in TD Fe film even grown on top of a PLD film. Our study indicates that the uniaxial magnetic anisotropy in Fe/GaAs(001) system can be controlled by a combination of TD and PLD growth.

Tuning magnetic anisotropies of Fe films on Si(111) substrate via direction variation of heating current

We adopted a novel method to tune the terrace width of Si(111) substrate by varying the direction of heating current. It was observed that the uniaxial magnetic anisotropy (UMA) of Fe films grown on the Si(111) substrate enhanced with decreasing the terrace width and superimposed on the weak six-fold magnetocrystalline anisotropy. Furthermore, on the basis of the scanning tunneling microscopy (STM) images, self-correlation function calculations confirmed that the UMA was attributed mainly from the long-range dipolar interaction between the spins on the surface. Our work opens a new avenue to manipulate the magnetic anisotropy of magnetic structures on the stepped substrate by the decoration of its atomic steps.

FMR Investigations on Magnetic Anisotropy in Epitaxial Fe Films Grown on GaAs(001) by Pulsed Laser Deposition

We report studies of magnetic anisotropy in Fe films of various thicknesses grown on GaAs(001) with MgO as a capping layer. Deposition was done in an ultrahigh vacuum chamber at room temperature. Ferromagnetic Resonance (FMR) has been used to investigate the anisotropy in the films. Fe films of thickness 20 monolayers (ML) and 25 ML showed the presence of both four-fold and in-plane uniaxial magnetic anisotropies. In Fe films of thickness as high as 50 ML the spectra showed different number of peaks at different in-plane angles of applied magnetic field. This could be understood as being due to the presence of a mixture of both uniaxial and four-fold anisotropies in the films. The anisotropy constants are evaluated. The interface of MgO with Fe is found to be one of the factors that influence the anisotropy towards a uniaxial nature.

Quantum Well States and Oscillatory Magnetic Anisotropy in Ultrathin Fe Films

The magnetic anisotropy of Fe film grown on vicinal Ag(1,1,10) surfaces studied with the in situ magneto-optic Kerr effect shows oscillatory behavior. We found that both the in-plane step-induced uniaxial anisotropy and the perpendicular anisotropy measured at low temperature show strong oscillations as a function of Fe thickness with a period of ~ 5.7 monolayers. Such novel oscillation of the anisotropy is attributed to the quantum well states (QWS) of d-band electrons at the Fermi level in the Fe film. These QWS have been observed by angle-resolved photoemission spectroscopy from a Fe wedge films grown on Ag(001) surface.

Revealing the volume magnetic anisotropy of Fe films epitaxied on GaAs(001) surface

The in-plane magnetic anisotropy in Fe films grown on GaAs(001) was investigated quantitatively by the magneto-optic Kerr effect with a rotating magnetic field. The clear 1/dFe relation of the uniaxial magnetic anisotropy indicates a surprising volume contribution with easy axis along the GaAs [11¯0] direction. Such volume anisotropy was found to be sensitive to the growth temperature and also strongly correlate with the interface anisotropy. Our results may introduce a new aspect for further understanding the origin of uniaxial magnetic anisotropy in Fe/GaAs(001) system.

Large amplitude oscillation of magnetic anisotropy engineered by substrate step density

Large amplitude quantum oscillations of magnetic anisotropy in Fe films grown on Ag surfaces of high step density are reported. Distortion of the film structure by the steps is found to be responsible for the anisotropy modification which oscillates with increasing film thickness. The larger the distorted fraction of the film volume, the larger the observed amplitude of the anisotropy oscillations. Such dependence of the anisotropy oscillations on the step density offers an easy tool to manipulate the strength of the anisotropy and orientation of the easy magnetization axis.

Oscillatory Magnetic Anisotropy Originating from Quantum Well States in Fe Films

The magnetic anisotropy of Fe film grown on vicinal Ag(1,1,10) surfaces was studied with the in situ magneto-optic Kerr effect. Below 200 K, strong oscillations of the uniaxial magnetic anisotropy as a function of Fe thickness with a period of 5.7 monolayers are found, which can even cause the easy magnetization axis to oscillate between perpendicular and parallel to the steps. Such novel oscillation of the anisotropy is attributed to the quantum well states of d-band electrons at the Fermi level in the Fe film. This is unlike the previously observed oscillatory behaviors of ferromagnetic films caused by the quantum well states in nonmagnetic interfacing layers.

Effect of obliquely evaporated Au cap layer on the magnetic properties of thin Fe films on Si(111)

The influence of Au capping layers on the magnetic properties of thin Fe films grown on Si(111) has been studied by means of room temperature magneto-optic Kerr effect (MOKE). MOKE measurements show a peculiar behavior of the magnetic anisotropy of Fe films grown at normal incidence and covered with obliquely evaporated Au cap layers. The magnetic anisotropy is dependent on the thickness of the deposited Au layer as well as on the growth conditions. First, the initial Fe sixfold in-plane magnetocrystalline anisotropy is replaced by an in-plane uniaxial one for Au thicknesses below 2 ML. Then, for increasing Au film thickness we observe an in-plane switching of the magnetic direction depending of the Au evaporation direction with respect to the substrate. Consider, for example, oblique Au depositions below 2 ML along the [1¯21¯]Si direction. These peculiar deposition conditions lead to a uniaxial anisotropy with easy axis perpendicular to the incidence plane of the Au flux. For thicker Au thicknesses, the uniaxial easy axis undergoes an in-plane switching reorientation of 90° corresponding to the Au evaporation direction. Angular resolved ultraviolet spectroscopy and ion scattering spectroscopy investigations reveal that this complex anisotropy behavior can be attributed partly to Au/Fe interfacial interdiffusion.

High frequency characteristics of soft magnetic Fe–O alloy thin films fabricated by helicon plasma sputtering

The effect of oxygen-doping has been studied on the magnetic properties of Fe thin films produced at room temperature by a helicon-plasma-enhanced RF magnetron sputter-deposition. A reduction in magnetic coercivity due to grain refinement was achieved using very low dose of oxygen, which did not lead to the formation of crystalline Fe oxides with the low saturation magnetization. Moreover, it was demonstrated that oxygen-doping also enhances the in-plane uniaxial magnetic anisotropy of Fe films and thus can be applied beneficially to increase high-frequency permeability which is needed in microwave applications.

Structural and Magnetic Properties of Ultrathin Fe Films onPt(001) Surface

Magnetic anisotropy evolution of ultrathin Fe films grown on Pt(001)single-crystal surface is investigated by UHV in situ surfacemagneto-optical Kerr effect (SMOKE) measurement. After annealing at~600 K, the magnetic anisotropy of Fe film switches from in-planeto perpendicular at low coverage, leading to a spin reorientationtransition (SRT). Meanwhile, in the range of 3–4 monolayer (ML)thickness, the coercivity of the Fe polar hysteresis loop decreasesdramatically. Further scanning tunnelling microscopy (STM) and lowenergy electron diffraction (LEED) investigation correlates themagnetic properties with the film structures. We attribute this SRT tothe formation of Fe–Pt ordered alloy.

Temperature dependence of the surface anisotropy of Fe ultrathin films on Cu(001).

We report an experimental approach to separate temperature dependent reversible and irreversible contributions to the perpendicular magnetic anisotropy of Fe films grown at low temperatures on Cu(001) substrates. The surface anisotropy K(S)(T) is found to decrease linearly with temperature, causing a thermally induced spin reorientation into the plane. The irreversible shift of the spin reorientation transition and the coercivity of the iron films are directly correlated to the increasing Fe island size during annealing. The increased coercivity is discussed in terms of domain wall energy inhomogeneities provided by the islands.

Non-monotonic step-induced magnetic anisotropy of Fe films prepared on vicinalAu(001) surfaces with different step orientations

We report on investigations of the crystallographic structure and the magneticanisotropies of epitaxial Fe films deposited on vicinal Au(001) surfaces for twomiscut directions and various miscut angles. The stepped surface generates auniaxial in-plane anisotropy contribution in addition to the fourfold anisotropycharacteristic for Fe(001). With the step edges perpendicular to [100]Fethe uniaxial anisotropy constant is a non-monotonic function of the vicinal angle.At low vicinal angles the easy magnetization axis is parallel to the step edges. Theeffective uniaxial anisotropy constant first increases and then decreases for increasingvicinal angle, crossing zero at about 1.3°± 0.2°. For higher angles the easy axis isperpendicular to the step edges. For the step edges perpendicular to [110]Fethe step-induced in-plane uniaxial anisotropy increases approximately linearlywith the vicinal angle.

Epitaxial Fe films on GaAs(001): Does the substrate surface reconstruction affect the uniaxial magnetic anisotropy?

The in-plane magnetic anisotropy of Fe films epitaxially grown on GaAs(001), in addition to a thickness-dependent four-fold contribution has a uniaxial component originating from the Fe/GaAs interface. This has been observed in several previous investigations. The orientation of the uniaxial easy axis (e.a.), however, was found to be along the [110] direction in most studies, but also an e.a. parallel to [−110] was reported in a few cases. It has been suggested that different reconstructions of the GaAs surface prior to Fe deposition could be responsible for this discrepancy. In the present contribution, it is shown that in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature the uniaxial anisotropy always has its easy axis along [110] with practically the same magnitude. In particular, the surface reconstruction of the GaAs substrate — either (4×2) or (2×6) — has no effect on the resulting uniaxial magnetic anisotropy. This [together with recent results related to the phase transition of Fe/GaAs(001)] suggests that the same atomic configuration is formed at the Fe/GaAs(001) interface in both cases connected with the segregation of a certain amount of As (and Ga) to the surface.