Thickness-dependent magnetic anisotropy in obliquely deposited Fe(001)/Pd thin film bilayers probed by VNA-FMR

The thickness-dependent magnetic anisotropy of obliquely deposited Fe(001)/Pd thin films on Mg(001) is investigated by fitting the field-dependent resonant field curve using the Kittel equation.In this study, three Fe film samples with thicknesses of 50 monolayers(ML), 45 ML, and 32 ML deposited at 0°, 45°, and 55°, respectively, are used.The magnetic anisotropy constant obtained from ferromagnetic resonance(FMR) spectra exhibits a dominant fourfold magnetocrystalline anisotropy(MCA) at the normal deposition angle with larger Fe thickness.However, the in-plane uniaxial magnetic anisotropy(UMA) is induced by a higher oblique deposition angle and a smaller thickness.Its hard axis lies between the [100] and [010] directions.The FMR data-fitting analysis yields a precise measurement of smaller contributions to the magnetic anisotropy, such as in-plane UMA.Due to MCA, when the magnetic field is weaker than the saturated field,the magnetization direction does not always align with the external field.The squared frequency-dependent resonant field measurement gives an isotropic Landé g-factor of 2.07.Our results are consistent with previous experiments conducted on the magneto-optical Kerr effect(MOKE) and anisotropic magnetoresistance(AMR) systems.Thus, a vector network analyzer ferromagnetic resonance(VNA-FMR) test-method for finding UMA in obliquely deposited Fe(001)/Pd bilayer ferromagnetic thin films, and determining the magnetic anisotropy constants with respect to the film normal deposition, is proposed.     

High frequency behaviours and Mssbauer study of field annealed FeCuNbSiB alloy ribbons

This paper investigates the high frequency behaviours and magnetic anisotropy of rapidly solidified FINEMET (Fe73.5Si13.5B9Nb3Cu1) alloy ribbons annealed in an applied magnetic field. It finds that the ribbons annealed with the applied magnetic field show much higher resonance frequencies and have even higher permeability at higher frequencies than the samples annealed without the magnetic field and the non-annealed ribbons. Mssbauer spectroscopy had been employed to study the spatial distribution of the magnetic moments of five selected FINEMET alloy ribbons in different heat-treated conditions. The results show that an easy plane has been established after annealling in the magnetic field, while for the other ribbons this effect is not significant. Hence, the relationship between magnetic field annealing and high frequency property has been bridged by the bianisotropic theory.     

Theoretical investigation of ferromagnetic resonance in a ferromagnetic thin film with external stress anisotropy

We use the ferromagnetic resonance(FMR)method to study the properties of ferromagnetic thin film,in which external stress anisotropy,fourfold anisotropy and uniaxial anisotropy are considered.The analytical expressions of FMR frequency,linewidth and the imaginary part of magnetic susceptibility are obtained.Our results reveal that the FMR frequency and the imaginary part of magnetic susceptibility are distinctly enhanced,and the frequency linewidth or field linewidth are broadened due to a strong external stress anisotropy field.The hard-axis and easy-axis components of magnetization can be tuned significantly by controlling the intensity and direction of stress and the in-plane uniaxial anisotropy field.     

Thickness dependent manipulation of uniaxial magnetic anisotropy in Fe-thin films by oblique deposition

The uniaxial magnetic anisotropy of obliquely deposited Fe(001)/Pd film on MgO(001) substrate is investigated as a function of deposition angle and film thickness. The values of incidence angle of Fe flux relative to surface normal of the substrate are 0°, 45°, 55°, and 70°, respectively. In-situ low energy electron diffraction is employed to investigate the surface structures of the samples. The Fe film thicknesses are determined to be 50 ML, 45 ML, 32 ML, and 24 ML(1 ML = 0.14 nm) by performing x-ray reflectivity on the grown samples, respectively. The normalized remanent magnetic saturation ratio and coercivity are obtained by the longitudinal surface magneto-optical Kerr effect. Here, the magnetic anisotropy constants are quantitatively determined by fitting the anisotropic magnetoresistance curves under different fields.These measurements show four-fold cubic anisotropy in a large Fe film thickness(50 ML) sample, but highly in-plane uniaxial magnetic anisotropies in thin films(24 ML and 32 ML) samples. In the obliquely deposited Fe films, the coercive fields and the uniaxial magnetic anisotropies(UMAs) increase as the deposition angle becomes more and more tilted. In addition, the UMA decreases with the increase of the Fe film thickness. Our work provides the possibility of manipulating uniaxial magnetic anisotropy, and paves the way to inducing UMA by oblique deposition with smaller film thickness.     

Magnetic properties of L1_0 FePt thin film influenced by recoverable strains stemmed from the polarization of Pb(Mg_(1/3)Nb_(2/3))O_3–PbTiO_3 substrate

The magnetic properties and magnetization reversible processes of L1_0 FePt(3 nm)/Pb(Mg_(1/3)Nb_(2/3))O_3–PbTiO_3(PMN–PT) heterostructure were investigated by using the phase field model. The simulation results show that the magnetic coercivities and magnetic domains evolution in the L1_0 FePt thin film are significantly influenced by the compressive strains stemming from the polarization of single crystal PMN–PT substrate under an applied electric field. It is found that the magnetic coercivities increase with increasing of the compressive strain. A large compressive strain is beneficial to aligning the magnetic moments along the out-of-plane direction and to the enhancement of perpendicular magnetic anisotropy. The variations of magnetic energy densities show that when compressive strains are different at the magnetization reversible processes, the magnetic anisotropy energies and the magnetic exchange energies firstly increase and then decrease, the negative demagnetization energy peaks appear at coercivities fields, and the magnetoelastic energies are invariable at large external magnetic field with the energy maximum appearing at coercivities fields. The variations of the magnetoelastic energies bring about the perpendicular magnetic anisotropy so that the magnetoelastic energy is lower at the large external magnetic fields, whereas the appearance of magnetoelastic energy peaks is due to the magnetization-altered direction from the normal direction of the plane of the L1_0 FePt thin film at coercivities fields.     

Improvement of high-frequency properties of Co2FeSi Heusler films by ultrathin Ru underlayer

Heusler Co2FeSi films with a uniaxial magnetic anisotropy and high ferromagnetic resonance frequency fr were deposited by an oblique sputtering technique on Ru underlayers with various thicknesses tRufrom 0 nm to 5 nm.It is revealed that the Ru underlayers reduce the grain size of Co2FeSi,dramatically enhance the magnetic anisotropy field HK induced by the internal stress from 242 Oe(1 Oe=79.5775 A·m^-1)to 582 Oe with an increment ratio of 2.4,while a low damping coefficient remains.The result of damping implies that the continuous interface between Ru and Co2FeSi induces a large in-plane anisotropic field without introducing additional external damping.As a result,excellent high-frequency soft magnetic properties with fr up to 6.69 GHz are achieved.     

High frequency behaviours and Mossbauer study of field annealed FeCuNbSiB alloy ribbons

This paper investigates the high frequency behaviours and magnetic anisotropy of rapidly solidified FINEMET （Fe73.5Si13.sBgNb3Cul） alloy ribbons annealed in an applied magnetic field. It finds that the ribbons annealed with the applied magnetic field show much higher resonance frequencies and have even higher permeability at higher frequencies than the samples annealed without the magnetic field and the non-annealed ribbons. MSssbauer spectroscopy had been employed to study the spatial distribution of the magnetic moments of five selected FINEMET alloy ribbons in different heat-treated conditions. The results show that an easy plane has been established after annealling in the magnetic field, while for the other ribbons this effect is not significant. Hence, the relationship between magnetic field annealing and high frequency property has been bridged by the bianisotropic theory.     

Enhancement of ferromagnetic resonance in Al_2O_3-doped Co_2FeAl Heusler alloy film prepared by oblique sputtering

Large and variable in-plane uniaxial magnetic anisotropy in a nanocrystalline(Co2FeAl)97.8(Al2O3)2.2soft magnetic thin film is obtained by an oblique sputtering method without being induced by magnetic field or post annealing. The in-plane uniaxial magnetic anisotropy varies from 50 Oe to 180 Oe(1 Oe = 79.5775 A·m-1) by adjusting the sample’s position. As a result, the ferromagnetic resonance frequency of the film increases from 1.9 GHz to 3.75 GHz.     

Enhancement of ferromagnetic resonance in Al203-doped CozFeAI Heusler alloy film prepared by oblique sputtering

Large and variable in-plane uniaxial magnetic anisotropy in a nanocrystalline （Co2FeA1）97.8（Al2O3）2.2 soft magnetic thin film is obtained by an oblique sputtering method without being induced by magnetic field or post anneaiing. The in-plane uniaxiai magnetic anisotropy varies from 50 Oe to 180 Oe （1 Oe=79.5775 A·m-1） by adjusting the sample＇s position. As a result, the ferromagnetic resonance frequency of the film increases from 1.9 GHz to 3.75 GHz.     

Magnetic anisotropy and magnetization reversal of ultrathin iron films with in-plane magnetization on Si（111） substrates

The magnetic anisotropy and magnetization reversal of single crystal Fe films with thickness of 45 monolayer (ML) grown on Si(111) have been investigated by ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM). Owing to the significant modification of the energy surface in remanent state by slight misorientation from (111) plane and a uniaxial magnetic anisotropy, the azimuthal angular dependence of in-plane resonance field shows a six-fold symmetry with a weak uniaxial contribution, while the remanence of hysteresis loops displays a two-fold one. The competition between the first and second magnetocrystalline anisotropies may result in the switching of in-plane easy axis of the system. Combining the FMR and VSM measurements, the magnetization reversal mechanism has also been determined.     

Origin of magnetization-induced anisotropy of magnetic films

It is proposed that the magnetization-induced anisotropy of magnetic films of cubic crystal structure originates from the anisotropy of atomic pair ordering, shape anisotropy, and strain anisotropy resulting from the constraint of the magnetostriction strain imposed on the film by the substratc. Calculated are the three anisotropy constants and their sum K vs temperature for Ni, Fe, and 55%Ni-Fe films; the room temperature （RT） constants vs the substrate temperature Tt during deposition or annealing after deposition for Ni and 50%Ni Co films; the RT constants vs com- position fraction for Fe-Ni films with Tt = RT, 250℃ and 450℃, Co Ni films at Tt = RT, 100℃ and 320℃, and Fe-Co films with Tt = RT and 300℃; the spread of RT K vs composition fraction for Fe Ni films; and RT △K/K vs composition fraction for Fe-Ni and Co Ni films, where △K denotes the variation of K of the film that is detached from its substrate. The calculated curves well accord with the measurements. The irrelevancy of K to the substrate material and the fast kinetics of the annealing in a field applied in the direction of the hard axis are explained reasonably.[第一段]     

Manipulating magnetic anisotropies of Co/MgO(001) ultrathin films via oblique deposition

We present a systematic investigation of magnetic anisotropy induced by oblique deposition of Co thin films on MgO(001) substrates by molecular beam epitaxy at different deposition angles,i.e.,0?,30?,45?,60?,and 75?with respect to the surface normal.Low energy electron diffraction(LEED),surface magneto–optical Kerr effect(SMOKE),and anisotropic magnetoresistance(AMR) setups were employed to investigate the magnetic properties of cobalt films.The values of in-plane uniaxial magnetic anisotropy(UMA) constant Ku and four-fold magnetocrystalline anisotropy constant K1 were derived from magnetic torque curves on the base of AMR results.It was found that the value of Ku increases with increasing deposition angle with respect to the surface normal,while the value of K_1 remains almost constant for all the samples.Furthermore,by using MOKE results,the Ku values of the films deposited obliquely were also derived from the magnetization curves along hard axis.The results of AMR method were then compared with that of hard axis fitting method(coherent rotation) and found that both methods have almost identical values of UMA constant for each sample.     

Switching Behaviour of Magnetic Particles with Dipolar Interaction

We study the switching in the magnetic moments of interacting magnetic particles. The dynamics of the magnetic moments is governed by a coupled set of Landau-Lifshitz-Gilbert equations. The magnetic particles are assumed to be spherical in shape, single domain, and have uniaxial anisotropy. Effects of dipolar interaction between the particles, anisotropy energy, an applied switching field with finite spatial extent and a small bias field are considered. When the separation between the particles is small, the dipolar field is significant and it affects the reversal of the magnetic moments. The final configuration attained depends sensitively on the decaying length of the switching field, the inter-particle separation, and the initial configuration. A bias field tends to suppress the effects of a spatially decaying switching field and dipolar interaction between neighbouring particles.     

Microwave ferromagnetic properties of as-deposited Co_2FeSi Heusler alloy films prepared by oblique sputtering

The Co2 FeSi films are deposited on Si(100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2 FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe–330 Oe(1 Oe = 79.5775 A·m-1), and low coercivities in a range of 5 Oe–28 Oe. As a result,high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films.These results indicate that Co2 FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.     

Optical response of an inverted InAs/GaSb quantum well in an in-plane magnetic field

The optical response of an inverted InAs/GaSb quantum well is studied theoretically. The influence of an in-plane magnetic field that is applied parallel to the quantum well is considered. This in-plane magnetic field will induce a dynamical polarization even when the electric field component of the external optical field is parallel to the quantum well.The electron–electron interaction in the quantum well system will lead to the de-polarization effect. This effect is found to be important and is taken into account in the calculation of the optical response. It is found that the main feature in the frequency dependence of the velocity–velocity correlation function remains when the velocity considered is parallel to the in-plane magnetic field. When the direction of the velocity is perpendicular to the in-plane magnetic field, the depolarization effect will suppress the oscillatory behavior in the corresponding velocity–velocity correlation function. The in-plane magnetic field can change the band structure of the quantum well drastically from a gapped semiconductor to a no-gapped semi-metal, but it is found that the distribution of the velocity matrix elements or the optical transition matrix elements in the wave vector space has the same two-tadpole topology.     

Evolution of magnetic domain structure of martensite in Ni–Mn–Ga films under the interplay of the temperature and magnetic field

Ferromagnetic shape memory Ni-Mn-Ga films with 7M modulated structure were prepared on MgO （001） substrates by magnetron sputtering. Magnetization process with a typical two-hysteresis loop indicates the occurrence of the reversible magnetic field-induced reorientation. Magnetic domain structure and twin structure of the film were controlled by the in- terplay of the magnetic and temperature field. With cooling under an out-of-plane magnetic field, the evolution of magnetic domain structure reveals that martensitic transformation could be divided into two periods： nucleation and growth. With an in-plane magnetic field applied to a thermomagnetic-treated film, the evolution of magnetic domain structure gives evidence of a reorientation of twin variants of martensite. A microstructural model is described to define the twin structure and to produce the magnetic domain structure at the beginning of martensitic transformation; based on this model, the relationship between the twin structure and the magnetic domain structure for the treated film under an in-plane field is also described.     

Angular control of multi-mode resonance frequencies in obliquely deposited CoZr thin films with rotatable stripe domains

We investigate the angular-dependent multi-mode resonance frequencies in CoZr magnetic thin films with a rotatable stripe domain structure.A variable range of multi-mode resonance frequencies from 1.86 GHz to 4.80 GHz is achieved by pre-magnetizing the CoZr films along different azimuth directions,which can be ascribed to the competition between the uniaxial anisotropy caused by the oblique deposition and the rotatable anisotropy induced by the rotatable stripe domain.Furthermore,the regulating range of resonance frequency for the CoZr film can be adjusted by changing the oblique deposition angle.Our results might be beneficial for the applications of magnetic thin films in microwave devices.     

X-Ray Magnetic Circular Dichroism Measurement of Fe-Co Alloy Films Prepared by Electrodeposition

The macro- and micro-magnetic properties of Fe-Co alloy films eletrodeposited on CaAs（100） are studied by synchrotron radiation x-ray magnetic circular dichroism （XMCD） in combination with the magneto-optical Kerr effect （MOKE） measurements and magnetic force microscopy （MFM）. The orbital and spin magnetic moments of each element in the Fe-Co alloy are determined by the sum rules of XMCD. Element-specific hysteresis loops （ESHL） are obtained by recording the La MCD signals as a function of applied magnetic field. MOKE results reveal that the amorphous films are magnetically isotropic in the surface plane. The MFM image shows that the dimension of the magnetic domains is about 1-2 #m, which is much larger than that of the grains, indicating that there are intergranular correlations among these grains. Both ESHL and MOKE hysteresis loops indicate the strong ferromagnetic coupling of Fe and Co in the alloy films.     

Effects of Ⅴ/Ⅲ ratio on species diffusion anisotropy inthe MOCVD growth of non-polar a-plane GaN films

Non-polar a-plane (110) GaN films have been grown on r-plane (102) sapphire substrates by metal organic chemical vapour deposition. The influences of Ⅴ/Ⅲ ratio on the species diffusion anisotropy of a-plane GaN films were investigated by scanning electron microscopy, cathodoluminescence and high-resolution x-ray diffraction measurements. The anisotropy of a-plane GaN films may result from the different migration length of adatoms along two in-plane directions. Ⅴ/Ⅲ ratio has an effect on the growth rates of different facets and crystal quality. The stripe feature morphology was obviously observed in the film with a high V/III ratio because of the slow growth rate along the [100] direction. When the Ⅴ/Ⅲ ratio increased from 1000 to 6000, the in-plane crystal quality anisotropy was decreased due to the weakened predominance in migration length of gallium adatoms.     

Anisotropic magnetoelastic response in the magnetic Weyl semimetal Co_3Sn_2S_2

Co_3Sn_2S_2 is a recently identified magnetic Weyl semimetal in Shandite compounds. Upon cooling, Co_3Sn_2S_2 undergoes a ferromagnetic transition with c-axis polarized moments(~0.3 μB/Co) around T_C= 175 K, followed by another magnetic anomaly around T_A≈ 140 K. A large intrinsic anomalous Hall effect is observed in the magnetic state below T_C with a maximum of anomalous Hall angle near T_A. Here, we report an elastic neutron scattering on the crystalline lattice of Co_3Sn_2S_2 in a magnetic field up to 10 T. A strongly anisotropic magnetoelastic response is observed, while only a slight enhancement of the Bragg peaks is observed when B//c. The in-plane magnetic field(B//ab) dramatically suppresses the Bragg peak intensity probably by tilting the moments and lattice toward the external field direction. The in-plane magnetoelastic response commences from T_C, and as it is further strengthened below T_A, it becomes nonmonotonic against the field between T_A and T_C because of the competition from another in-plane magnetic order. These results suggest that a magnetic field can be employed to tune the Co_3Sn_2S_2 lattice and its related topological states.