用铁磁共振方法同时测定单晶外延膜的Ku和K1

本文导出了兼具沿晶面法向感生单轴各向异性(K_u)和立方磁晶各向异性(K₁)的任一晶面沿任一方向的薄膜共振场公式,从而提出了同时测定K_u和K₁的一种方法。以(111)晶面为例,给出了具体方法和实验结果。     

Development of magnetic anisotropies in ultrathin epitaxial films of Fe(001) and Ni(001)

Ultrathin films, bcc Fe(001) on Ag(001), fcc Fe(001) on Cu(001) and Fe/Ni(001) bilayers on Ag, were grown by molecular beam epitaxy. A wide range of surface science tools were employed to establish the quality of epitaxial growth. Ferromagnetic resonance and Brillouin light scattering were used to extract the magnetic properties. Emphasis was placed on the study of magnetic anisotropies. Large uniaxial anisotropies with easy axis perpendicular to the film surface were observed in all ultrathin structures studied. These anisotropies were particularly strong in fcc Fe and bcc Fe films. In sufficiently thin samples the saturation magnetization was oriented perpendicularly to the film surface in the absence of an applied field. It has been demonstrated that in bcc Fe films the uniaxial perpendicular anisotropy originates at the film interfaces. In situ measurements indentified the strength of the uniaxial perpendicular anisotropy constant at the Fe/vacuum, Fe/Ag and Fe/Au interfaces asK _us = 0.96, 0.63, and 0.3 ergs/cm² respectively. The surface anisotropies deduced for [bulk Fe/noble metal] interfaces are in good agreement with the values obtained from ultrathin films. Hence the perpendicular surface ansiotropies originate in the broken symmetry at abrupt interfaces. An observed decrease in the cubic anisotropy in bcc Fe ultrathin films has been explained by the presence of a weak 4th order in-plane surface anisotropy,K _1S=0.012 ergs/cm². Fe/Ni bilayers were also investigated. Ni grew in the pure bcc structure for the first 3–6 ML and then transformed to a new structure which exhibited unique magnetic properties. Transformed ultrathin bilayers possessed large inplane 4th order anisotropies far surpassing those observed in bulk Fe and Ni. The large 4th order anisotropies originate in crystallographic defects formed during the Ni lattice transformation.     

Ferromagnetic resonance in a uniaxial magnetic film subjected to magnetic biasing along its hard axis

The precession dynamics of the magnetization of a film with an in-plane uniaxial anisotropy is analyzed in the spectrum of ferromagnetic resonance corresponding to magnetic biasing along the hard axis of the film. An additional resonance peak is revealed near magnetic anisotropy field H _u . This peak is related to the appearance of angular bistability due to the presence of two symmetric angular equilibrium positions in field H < H _u .     

Solid-state reactions in Ga/Mn thin films: Formation and magnetic properties of the ϕ-Ga<Subscript>7.7</Subscript>Mn<Subscript>2.3</Subscript> phase

Experimental results concerning the solid-state synthesis of the ϕ-Ga_7.7Mn_2.3 phase in Ga/Mn thin films are presented. A ferromagnetic (or ferrimagnetic) state is observed in the samples annealed at temperatures above 250°C. The X-ray diffraction studies demonstrate the formation of the ϕ-Ga_7.7Mn_2.3 phase, which is poly-crystalline being grown on glass substrates and exhibits the preferential cube-on-cube orientation on MgO(001) substrates. A strong dependence of the perpendicular anisotropy constant K _⊥ and of the effective biaxial anisotropy constant K ₁^eff on the magnetic field H has been found. Owing to such dependence, the easy axis of magnetization lying in the plane of the film changes its direction approaching the film normal when the increasing magnetic field exceeds 8 kOe. The anomalous behavior of K _⊥ and K ₁^eff constants is explained both by the in-plane stresses arising in the course of the formation of the ϕ-Ga_7.7Mn_2.3 phase and by the direct dependence of magnetostriction constants on the magnetic field. For the ϕ-Ga_7.7Mn_2.3 phase, the saturation magnetization M _S has been determined and the first magnetocrystalline anisotropy constant K ₁ has been estimated.     

The effect of (00l) crystal plane orientation on the thermoelectric properties of Bi2Te3 thin film

Highly (00l)-oriented pure Bi₂Te₃ films with in-plane layered grown columnar nanostructure have been fabricated by a simple magnetron co-sputtering method. Compared with ordinary Bi₂Te₃ film and bulk materials, the electrical conductivity and Seebeck coefficient of such films have been greatly increased simultaneously due to raised carrier mobility and electron scattering parameter, while the thermal conductivity has been decreased due to phonon scattering by grain boundaries between columnar grains and interfaces between each layers. The power factor has reached as large as 33.7 μW cm⁻¹ K⁻², and the out-of-plane thermal conductivity is reduced to 0.86 W m⁻¹ K⁻¹. Our results confirm that tailoring nanoscale structures inside thermoelectric films effectively enhances their performances.     

Ferromagnetic resonance in a gallium substitued garnet film

The ferromagnetic resonance at X, K and Q-band has been studied on LPE₁₁₁ films of composition Y₃Fe_4.2Ga_0.8O₁₂. From the in-plane measurement and measurement in a 11¯2 plane theg-factor,g=2-02 (K, Q),g=2·05 (X band), the total uniaxial anisotropy fieldB _A (80 K)=750 G (75 mT),B _A (300 K)=250 G (25 mT) and the cubic field 2K ₁/M have been dstermined. Besides of the main resonance with the linewidth B =15 G (1·5 mT), B =50 G (5 mT), B _min=10·5 G (1·05 mT) a linear spin-wave spectrum and some high-field modes were observed. A new approximate method of crystal orientation in the plane of the film has been used based on the analysis of the in-plane dependence of the resonance field.The authors wish to express their thanks to Dr. S.Krupika for helpful discussions.     

Analysis of the boundary problem of SSWR in asymmetric isotropic insulator films

The influence of various combinations of the uniaxial surface anisotropy constantsK _s1 andK _s2 on the angular dependence of the standing spin-wave resonance (SSWR) spectrum is studied for an isotropic insulator film with asymmetrically pinned spins. It is shown that the (K _s1,K _s2)-plane can be divided into zones in which the angular dependence of the SSWR spectrum has different characteristic features. These features are studied in detail.Dedicated to Academician Vladimír Hajko on the occasion of his 65th birthday.     

FMR study of the anisotropic properties of an epitaxial Fe<Subscript>3</Subscript>Si film on a Si(111) vicinal surface

The anisotropic characteristics of an iron silicide (Fe₃Si) epitaxial thin magnetic film grown on a Si(111) silicon vicinal surface with a misorientation angle of 0.14° have been measured by the ferromagnetic resonance method. It has been shown that the polar and azimuth misorientation angles of the crystallographic plane of the substrate can be determined simultaneously from the angular dependences of the ferromagnetic resonance field of the epitaxial film. The effective saturation magnetization of the film M _eff = 1105 G and the constant of the cubic magnetocrystalline anisotropy K ₄ = 1.15 × 10⁵ erg/cm³ have been determined. The misorientation of the substrate plane leads to the formation of steps on the film surface and, as a result, to the appearance of uniaxial magnetic anisotropy of the magnetic dipole nature with the constant K ₂ = 796 erg/cm³. Small unidirectional magnetic anisotropy (K ₁ = 163 erg/cm³), which may be associated with symmetry breaking on the steps of the film and is due to the Dzyaloshinskii–Moriya interaction, has been detected.     

New features from transparent thin films of EuTiO3

ABSTRACT

The almost multiferroic perovskite EuTiO₃ (ETO) has been prepared as films on substrates of SrTiO₃. For all prepared film thicknesses highly transparent insulating films with atomically flat surfaces and excellent orientation have been grown. They were characterized by X-ray diffraction, magnetic susceptibility and birefringence measurements and found to exhibit bulk properties, namely an antiferromagnetic transition at T_N = 5.1 K and a structural transition at T_S = 282 K. The latter could only be identified due to the high transparency of the samples since the optical band gap is of the order of 4.5 eV and larger than observed before for any bulk and thin film samples.     

Ferromagnetic resonance study of sputtered Co|Ni multilayers

We report on room temperature ferromagnetic resonance (FMR) studies of [ t Co|2t Ni]  × N sputtered films, where 0.1 ≤ t ≤ 0.6 nm. Two series of films were investigated: films with the same number of Co|Ni bilayer repeats (N = 12), and samples in which the overall magnetic layer thickness is kept constant at 3.6 nm (N = 1.2/t). The FMR measurements were conducted with a high frequency broadband coplanar waveguide up to 50 GHz using a flip-chip method. The resonance field and the full width at half maximum were measured as a function of frequency for the field in-plane and field normal to the plane, and as a function of angle to the plane for several frequencies. For both sets of films, we find evidence for the presence of first and second order anisotropy constants, K₁ and K₂. The anisotropy constants are strongly dependent on the thickness t, and to a lesser extent on the total thickness of the magnetic multilayer. The Landé g-factor increases with decreasing t and is practically independent of the multilayer thickness. The magnetic damping parameter α, estimated from the linear dependence of the linewidth ΔH, on frequency, in the field in-plane geometry, increases with decreasing t. This behaviour is attributed to an enhancement of spin-orbit interactions with decreasing Co layer thickness and in thinner films, to a spin-pumping contribution to the damping.     

Theoretical analysis of trends in hydrogen bonding involving halogen acceptors (F−At) covalently bonded to a group 14 atom (C−Pb)

In this work, extensive quantum-chemical calculations have been carried out to identify and elucidate trends in the hydrogen-bonding (HB) interaction involving halogen acceptors covalently bonded to a group 14 atom. A series of 25 heterodimers composed of MH₃X (where M = C?Pb and X = F?At) and HNC molecules have been selected as model complexes stabilised by the HB interaction occurring between the X atom of MH₃X and the H atom of HNC. The interaction energy (E_int) between MH₃X and HNC in the MH₃X···HNC complexes falls in the range from ?2.7 to ?10.8 kcal/mol, indicating weak or medium strength of HB in these complexes. The strength of HB in the complexes remains consistent with the well-known HB weakening as X gets heavier. Regarding the effect of M on E_int, the gradual strengthening of HB is observed while descending group 14, but only from M = Si to M = Pb. The trends in E_int are compared with various HB-related parameters obtained from vibrational analysis, the natural bond orbital (NBO) method, the symmetry-adapted perturbation theory (SAPT) and the quantum theory of atoms in molecules (QTAIM). The parameters that present clear (possibly linear) relationships with E_int have been selected to characterise the effect of M and X on the HB interaction.     

Magnetic anisotropy in (, .44, .55, .67, and .78) alloy film grown on and MgO(001) by molecular beam epitaxy

Fe_xPd_1−x (x=.30, .44, .55, .67, and .78) films were directly grown on SrTiO₃(001) and MgO(001) by molecular beam epitaxy at 500 C. The thickness of all films is 50 nm. X-ray diffraction shows epitaxial quality and face-center- tetragonal (00l), (002), and (003) peaks indicating an FePd L1₀ order state for films of x=.30, .44 and .55. X-ray diffraction only shows (002) peaks with a relatively weak intensity for the film of x=.67 and no (00l) peak is observed, but a broad body-center-cubic Fe(002) is identified for the film of x=.78. Magnetic hysteresis curves are carried out by a vibrating sample magnetometer (VSM) with an applied field within 12 kOe. Magnetization of both in-plane and perpendicular-to- the-plane measurements show a linear increase of the magnetization saturation from 560 emu/cm³ to 1250 emu/cm³ as x increasing from .30 to .78. For the results of the in-plane measurements, remanence (M_r), however, shows a minimum while the anisotropy field (H_k) shows a maximum for the film with x=.44 indicating the optimal content ratio of Fe/Pd for perpendicular anisotropy in the present alloy films. Further, negative remanence is observed in the hysteresis curves where the field is perpendicular to the film of x=.78 This may indicate that the L1₀order state still affects the magnetic anisotropy for high Fe content films even though the film has a body-center-cubic structure.     

The amplification of far-infrared radiation on optically excited p-type germanium

The far-infrared spectrum of cyclotron resonance absorption in the valence band of p-type germanium has been calculated using 6 × 6 k*p Hamiltonian for degenerate valence band for magnetic field 20T and lattice temperature 77K. That has been shown that excitation by pulseCO ₂ laser radiation can lead to the amplification on light hole cyclotron resonance.     

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.     

The magnetic anisotropy of cold-rolled and as-quenched amorphous (Fe1−x Ni x )78Si10B12 alloy systems

In order to make clear the origin of magnetic anisotropy of amorphous alloys produced by a single roller quenching method, the composition dependence of the in-plane magnetic anisotropy of cold-rolled and as-quenched amorphous (Fe₁− _x Ni _x )₇₈Si₁₀B₁₂ alloy systems was studied at room temperature. The twofold in-plane magnetic anisotropy constantK _u of cold rolled and as-quenched specimen decreases with increase inx at the Fe-rich side, and increases drastically at aboutx=0.2. Beyondx=0.25,K _u decreases gradually with further increase inx. From this study, it is emphasized that there is a clear correspondence between the atomic ratio of Fe to Ni at which the anomaly in magnetic anisotropy of the amorphous alloy occurs and the position of the fcc/bcc phase boundary in the Fe−Ni metal alloy system.     

In-plane structural order of domain engineered La0.7Sr0.3MnO3 thin films

We present a detailed structural study of tensile-strained La_0.7Sr_0.3MnO₃ thin films. We use the substrate miscut to control the number of rhombohedral variants in the films and study the in-plane order and structural distortions. Using high-resolution X-ray diffraction, we demonstrate that step-edge induced lattice modulations occur in 4-variant films, whereas periodic twinning is the dominant in-plane order for 2-variant films. We show that the in-plane twinning angle is almost completely relaxed. However, the relaxation of shear strain by the out-of-plane twinning angle and the monoclinic distortion is only partial. Furthermore, the film thickness dependence of the domain width reveals that domain formation is a universal mechanism for shear strain relaxation. Finally, we show that the structural response to the transition from the paramagnetic to the ferromagnetic phase of La_0.7Sr_0.3MnO₃ at 345?K is smaller in 4-variant films compared to 2-variant films.     

High-frequency characteristics of CoFeVAlONb thin films

High-frequency characteristics of CoFeVAlONb thin films were studied. A thin film of Co_43.47Fe_35.30V_1.54Al_5.55O_9.93Nb_4.21 is observed to exhibit excellent magnetic properties; magnetic coercivity of 1.24 Oe, uniaxial in-plane anisotropy field of 66.99 Oe, and saturation magnetization of 19.8 kG. The effective permeability of the film is as high as 1089 and is stable up to 1.8 GHz, and with ferromagnetic resonance over 3 GHz. This film also has very high electrical resistivity of about 628 μΩ cm. These superior properties make it ideal for high-frequency magnetic applications.     

Ferrimagnetic resonance spectra of magnetic bubble films at low microwave frequencies

Magnetic bubble films exhibit a number of ferrimagnetic resonance modes due to the spatial variation of the anisotropy. The resonance frequencies have been measured as a function of the applied bias fieldH ₀. In the lower field range the magnetization of the transient layer, which has negative anisotropy, is not yet parallel toH ₀. In this range the resonance frequencies are shifted to higher values due to pinning effects. In films grown by the vertical dipping method an additional layer on top of the transient layer is observed within which the magnetization rotates from the direction in the transient layer to that of the bulk of the film. In films grown by horizontal dipping no such layer could be detected. Each ferrimagnetic resonance mode excites transverse elastic waves in the film due to the magnetoelastic interaction and thus gives rise to elastic resonances of the whole crystal, film and substrate. These elastic resonances lead to a fine-structure of the ferrimagnetic resonances. The observed fine-structure vanishes periodically with frequency and from this behaviour the thickness of the magnetic film and of the transient layer has been determined.     

外应力场下双层铁磁薄膜中的铁磁共振性质

用铁磁共振方法得到了双层铁磁薄膜的色散关系解析表达式.发现共振场依赖于层间耦合强度和应力场.假定层间为反铁磁性耦合，且铁磁层Ａ有较强的平面内各向异性.随着外磁场的增强，铁磁层Ｂ中的磁化强度突然由最初的反平行转为平行，从而导致色散曲线的阶跃，并且发现光学模阶跃幅度比声学模大.随着应力场的增强，Ｂ层中磁化强度反转所需的外磁场减弱.此外，在不同的交换耦合强度和应力场下，光学模共振场对外磁场方向的依赖性较强. 关键词： 双层铁磁薄膜 界面相互作用 应力各向异性场 铁磁共振     

Magnetocrystalline anisotropy of MnF2 deduced from static torque

The first anisotropy constant K₁ as well as the differential susceptibility ΔX = Xχ - X∥ of MnF₂ has been determined from static torque measurements. The temperature range was for K₁ 4.2 K to 66 K and for ΔX 4.2 K to 300 K. The result for K₁ is in good agreement with values obtained from antiferromagnetic resonance experiments. In order to explain the differential susceptibility in the paramagnetic region, it was found necessary to take the g-factor anisotropy into account.