基片对交替溅射制备的MnZn铁氧体薄膜结构和磁性的影响

使用成分分别为MnFe₂O₄和ZnFe₂O₄的靶,使用射频溅射交替沉积制备了成分不同的Mn_1-xZn_xFe₂O₄薄膜,沉积薄膜所用基片分别为单晶硅Si（100）,氧化的单晶硅SiO₂/Si（100）, ZnFe₂O₄为衬底的单晶硅ZnFe< 关键词： MnZn铁氧体 纳米晶 软磁性 磁性薄膜     

On the magnetoelastic contribution to the magnetic anisotropy of thin epitaxial Permalloy films: an ab initio study

Permalloy films are often used in the magnetic thin film technology. It is expected that in this material the magnetoelastic coupling of the magnetization to the epitaxial film strain does not produce undesired magnetic anisotropy, because the linear magnetoelastic bulk coefficient B₁ of Permalloy is near-zero. It is shown by means of the ab initio density functional electron theory that the nonvanishing nonlinear magnetoelastic couplings also do not lead to a considerable anisotropy. Explicit values for two of the nonlinear magnetoelastic coupling coefficients are given.     

Magnetische grenzflächen-anisotropie von amorphem Fe in kontakt mit nichtmagnetischen metallen

The magnetic properties of very thin ferromagnetic Fe films (1–10 atomic layers) in contact with nonmagnetic amorphous metals are investigated. Apart from the demagnetization energy, which supports a magnetization in the plane of the film, an energy of magnetic anisotropy occurs in the interlayer, which has the tendency to orient the magnetization perpendicular to the surface. The anomalous Hall effect of the ferromagnetic films is used to investigate their magnetic properties. From the measurements, we get the applied magnetic field B_s, which is necessary to orient the magnetization perpendicular to the film surface. In addition to a constant term, B_s is proportional to 1/d, which is typical of surface effects and yields the energy of the interface anisotropy. The value of this energy is strongly dependent on the nonmagnetic metal and is smaller for the system Pb/Fe than for Sn/Fe. Furthermore, the experimental results show no drastic reduction of the atomic magnetic moment in the surface layer.     

Magnetic anisotropy of epitaxial Fe layers grown on Si(0 0 1)

The magnetic properties of epitaxial iron films up to 80 monolayers (ML) thickness grown on Si(0 0 1) by using a template technique were investigated by means of superconducting quantum interference device and magneto-optic Kerr effect techniques. The thinnest films investigated (∼3 ML) exhibit a composition close to Fe₃Si with a Curie temperature below room temperature (RT) and strong out-of-plane remanent magnetization that reflects the presence of a dominant second order surface anisotropy term. Thicker films (⩾4 ML) are ferromagnetic at RT with remanent magnetization in film-plane and a composition closer to pure Fe with typically 8–10% silicon content. When deposited at normal incidence such films show simple in-plane fourfold anisotropy without uniaxial contribution. The relevant fourth-order effective anisotropy constant K₄^eff was measured versus film thickness and found to change its sign near 18 ML. The origin of this remarkable behavior is investigated by means of a Néel model and mainly traced back to fourth-order surface anisotropy and magneto-elastic effects related to the large biaxial in-plane compressive strain up to 3.5% in the thinnest (⩽25 ML) films.     

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.     

Role of crystal orientation on the magnetic properties of CoFe2O4 thin films grown on Si (1 0 0) and Al2O3 (0 0 0 1) substrates using pulsed laser deposition

We report the influence of crystal orientation on the magnetic properties of CoFe₂O₄ (CFO) thin films grown on single crystal Si (1 0 0) and c-cut sapphire (Al₂O₃) (0 0 0 1) substrates using pulsed laser deposition technique. The thickness was varied from 200 to 50 nm for CFO films grown on Si substrates, while it was fixed at 200 nm for CFO films grown on Al₂O₃ substrates. We observed that the 200 and 100 nm thick CFO-Si films grew in both (1 1 1) and (3 1 1) directions and displayed out-of-plane anisotropy, whereas the 50 nm thick CFO-Si film showed only an (1 1 1) orientation and an in-plane anisotropy. The 200 nm thick CFO film grown on an Al₂O₃ substrate was also found to show a complete (1 1 1) orientation and a strong in-plane anisotropy. These observations pointed to a definite relation between the crystalline orientation and the observed magnetic anisotropy in the CFO thin films.     

Induced magnetic anisotropy in Co-doped Finemet-type nanocrystalline materials

Transverse magnetic anisotropy has been induced in the Fe_14.7Co_58.8Cu₁Nb₃Si_13.5B₉ and Fe_13.8Co₆₅Cu_0.6Nb_2.6Si₉B₉ amorphous ribbons by annealing under an external magnetic field. This anisotropy plays a predominant role, compared to magneto-crystalline and magneto-elastic anisotropies, in forming the magnetic properties and shaping the hysteresis loop. The effect of temperature and time of annealing on the induced magnetic anisotropy and magnetic properties (magnetic permeability, coercivity and power losses) in both alloys was investigated. Under this work, measurements of frequency dependence of the real and imaginary parts of magnetic permeability were made within a frequency range up to 110 MHz. It was found that as a result of magnetic field annealing the Snoek limit increases in both alloys compared to the Co-free Finemet.     

Magnetic interface-anisotropy of amorphous iron in contact with nonmagnetic metals

The magnetic properties of very thin ferromagnetic Fe films (1–10 atomic layers) in contact with nonmagnetic amorphous metals are investigated. Apart from the demagnetization energy, which supports a magnetization in the film plane, an energy of magnetic anisotropy occurs in the interlayer, which has the tendency to turn the magnetization perpendicular to the surface. The anomalous Hall effect of the ferromagnetic films is used to investigate their magnetic properties. From the measurements we get the applied magnetic fieldB _s , which is necessary to turn the magnetization perpendicular to the film surface.B _s is, besides a constant term, proportional to 1/d, which is typical of surface effects and yields the energy of the interface anisotropy. The value of this energy is strongly dependent on the nonmagnetic metal and is smaller for the system Pb/Fe than for Sn/Fe. Furthermore, the experimental results show no drastic reduction of the atomic magnetic moment in the surface layer.     

Aluminium diffusion in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained (B ₊ films) film structures, respectively, have been examined as diffusion barriers for preventing aluminium diffusion. The aluminium diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) at temperatures up to 550° C. The diffusivity from 300° C to 550° C is: D[m²s^–1]=3×10^–18 exp[–30/(RT)] in B ₀ layers and D[m²s^–1]=1.4×10^–16 exp[–48/(RT)] in B ₊ TiN layers. The activation-energy values determined indicate a grain boundary diffusion mechanism. The difference between the diffusion values is determined implicitly by the microstructure of the layers. Thus, the porous B ₀ layers contain a considerable amount of oxygen absorbed in the intercolumnar voids and distributed throughout the film thickness. As found by AES depth profiling, this oxygen supply allows the formation of Al₂O₃ during annealing the latter preventing the subsequent diffusion of the aluminium atoms.     

Effect of nitrogen concentration on the magnetic properties of Fe-Ta-N thin films

Soft magnetic nanocrystalline thin films with a high content of Ta (10 wt %) are synthesized by the method of reactive RF magnetron sputtering with subsequent annealing. It is established that the microstructure and magnetic properties of the films depend on the nitrogen partial pressure during sputtering and on the annealing temperature. Annealing of the amorphous films leads to the formation of α-Fe nanocrystallites whose properties and interactions determine the film parameters. A decrease in the α-Fe grain size to a level below the length of ferromagnetic exchange interaction sharply increases the magnetic softness. The role of nitrogen ions in the formation of a α-Fe nanocrystallite structure and uniaxial magnetic anisotropy of Fe-Ta-N films is established. The optimum technological regimes of deposition and annealing of the Fe-Ta-N films are determined, which ensure the synthesis of Fe-Ta-N nanocrystalline thin films with a high magnetic softness (B _s=1.6 T, H _c=0.2 Oe, and μ₁(1 MHz)=3400).     

Investigation of the magnetic properties and magnetic structure parameters of nanocrystalline Fe<Subscript>79</Subscript>Zr<Subscript>10</Subscript>N<Subscript>11</Subscript> films

The magnetic properties (magnetization curve, ferromagnetic resonance spectrum) of nanocrystalline Fe₇₉Zr₁₀N₁₁ films obtained by RF magnetron sputtering with subsequent annealing were studied experimentally, along with the fundamental magnetic constants of these films (saturation magnetization M _S, local magnetic anisotropy energy K, and the exchange coupling constant A). The magnetic properties are discussed within the random magnetic model, which determines the correlation of the magnetic properties with the fundamental magnetic constants and nanostructure parameters (grain size, magnetic anisotropy, and correlation radius R _C). The exchange correlation length 2R _L for the film magnetic microstructure was determined by correlation magnetometry.     

A comparison of the magnetic anisotropy of [001] and [111] oriented Co/Pd Multilayers

Superlattices of [001]_fcc Co/Pd with varying Co thicknesses from one to eight atomic layers per modulation period were epitaxially grown on NaCl by vapour deposition in UHV. Transmission electron diffraction indicates lattice coherence between the Co and the Pd layers for Co thicknesses up to six atomic layers. If deposited at a substrate temperatureT _s=50°C, only the superlattices containing Ci-monolayers show perpendicular magnetization. By raisingT _s to 200°C, the perpendicular anisotropy for Co monolayers is increased, and is also observed for Co bilayers. We suggest that this is due tolayer smoothening, which increases Néel's interface anisotropy. For more than 6 atomic layers of Co a loss of coherence is observed atT _s=50°C, accompanied by a structure transformation to hcp Co with a (0001)_Co(111)_Pd orientation.Non-epitaxial polycrystalline [111]-multilayers have a different anisotropy versus thickness behaviour. For such multilayers the range of Co thicknesses giving perpendicular magnetization is extended from 8 Å up to 12 Å atT _s=200°C. The different behaviour of the single crystal [001] films is caused by a strong volume contribution to the anisotropy, which favours in-plane magnetization, opposing the perpendicular interface anisotropy. This easy-plane term is attributed to magneto-elastic anisotropy due to stretching of the Co layers, via a positive magnetostriction.     

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.     

Local magnetic properties of ultrathin ferromagnetic fcc-Fe-films on Cu(001)

Conversion electron Mössbayer spectroscopy (CEMS) on three monolayers (ML) thick metastable fcc-Fe(001) films grown epitaxially on a Cu(001) substrate under different conditions shows that these films are characterized by a distributionP(B _hf) of magnetic hyperfine fieldsB _hf. The vast majority of⁵⁷Fe nuclei experience relatively large hyperfine fields at low temperature. The temperature dependence of the most probable fieldB _peak was found to follow aT ^3/2 spin-wave law below 300 K. It is shown from the relative line intensities that preferential Fe spin orientation perpendicular to the film plane exists in films grown at 120 K, while preferential in-plane spin orientation is found for a growth temperature of 300 K. Coating a low-temperature grown Fe film by 2 ML of Cu(001) drastically reduces the hyperfine field, in contrast to the case of room-temperature grown Cu-coated films.Dedicated to Professor Ulrich Gonser on the occasion of his 70th birthday     

Epitaxial strain-induced magnetic anisotropy in Sm3Fe5O12 thin films grown by pulsed laser deposition

Sm₃Fe₅O₁₂ thin films of various thicknesses were grown on a (0 0 1)-oriented Gd₃Ga₅O₁₂ substrate by pulsed laser deposition. The crystal structure of the films was strongly dependent on film thickness. The lattice was strained for thinner films due to a lattice mismatch between the film and substrate. This lattice strain was relaxed when the film thickness exceeded a critical thickness of around 660 Å. It is suggested that the epitaxial strain induces uniaxial magnetic anisotropy with an out-of-plane magnetic easy axis.     

Brillouin scattering from ultra thin iron films

The spin-wave excitations of ultrathin iron films (1 to 5 nm) on sapphire substrates have been studied by inelastic light scattering using Brillouin spectroscopy. The room temperature magnetization J, magnetic anisotropy field B_an, and the g-factor have been determined by fitting the measured ω-B results for surface spin waves to the related Damon-Eshbach theory. For thicknesses below 4 nm the film magnetization J_f decreases linearly with film thickness and is found substantially smaller than J_f values determined by static magnetization measurements. Equivalent reductions in J_f, however, were also obtained in light scattering studies of ultrathin Fe films on GaAs substrates reported previously in the literature [2].     

Some recent results on high-temperature superconductors: The Dutch scene

For the high-T _c superconductor La_1.85Sr_0.15CuO₄, we present results for the low-field magnetization and the lower and upper critical fieldsB _c1 (T) andB _c2(T). ForB _c1 (0) we find a value of about 20 mT. Extrapolating our resistive data for the transition midpoint taken in fields up to 12 T, we deduce a value of about 50 T forB _c2 (0). TheB _c2 values obtained by inductive measurements are significantly lower. We explain this by a largeB _c2 anisotropy due to the layered structure of these compounds. Losses in the Meissner state observed in magnetization and susceptibility measurements disappear after powdering the sample. This is taken as strong evidence for intergrain Josephson coupling in the bulk sample.     

Magnetic properties and domain structures of FeSiB thin films

Smooth Fe₇₈Si₁₀B₁₂ thin films were prepared by r.f. sputtering with the very slow deposition rate of 0.59 nm/min. The as-deposited films were not fully amorphous, instead α-Fe(Si) nanocrystallites were found to be embedded in the amorphous matrix. The saturation magnetostriction λ_s of the as-deposited film is about 6.5 × 10⁻⁶. After annealing at 540 °C for 1 h in an ultrahigh vacuum (4.5 × 10⁻⁵ Pa), the fraction of α-Fe(Si) crystalline phase largely increased, and correspondingly the λ_s decreased to 4.5 × 10⁻⁷. Ripple domain structures were observed in the as-deposited film, while dense stripe domains were observed in the annealed sample, characterized by a very narrow domain width of 80 nm. (1 1 0) texture and island-like configuration of α-Fe(Si) nanocrystallites formed by the annealing treatment are responsible for the perpendicular anisotropy. For the as-deposited film, the magnetization curves increased linearly with the increase of the magnetic field, and showed the very small hysteresis. On the other hand, the annealed sample clearly showed a very steep jump near the origin, which is due to the switch process of the dense stripe domain.     

Anisotropy effects in the A-15 superconductor Nb3Sn

Experimental B_c2(T) characteristics of two Nb₃Sn samples are analyzed using a full strong coupling theory of B_c2(T) which also includes anisotropy effects. The analysis requires a rather pronounced anisotropy of the electron-phonon interaction and of the Fermi velocity and Pauli paramagnetic limiting in order to reproduce the experimental B_c2(T) data over the whole temperature range. The analysis of the second, dirty sample shows that a pronounced change in the electron density of states at the Fermi energy is required together with reduction of the Fermi velocity anisotropy to reproduce the experimental B_c2(T) data. The analysis does not require any contributions from spin-orbit scattering processes to achieve an excellent match between theory and experiment.     

Structure,magnetic properties and magnetostriction of Fe81Ga19 thin films

The structure, magnetic properties and magnetostriction of Fe₈₁Ga₁₉ thin films have been investigated by using X-ray diffraction analysis, scanning electron microscope (SEM), vibrating sample magnetometer and capacitive cantilever method. It was found that the grain size of as-deposited Fe₈₁Ga₁₉ thin films is 50–60 nm and the grain size increases with increase in the annealing temperature. The remanence ratio (M_r/M_s) of the thin films slowly decreases with increase in the annealing temperature. However, the coercivity of the thin films goes the opposite way with increase in the annealing temperature. A preferential orientation of the Fe₈₁Ga₁₉ thin film fabricated under an applied magnetic field exists along 〈1 0 0〉 direction due to the function of magnetic field during sputtering. An in-plane-induced anisotropy of the thin film is well formed by the applied magnetic field during the sputtering and the formation of in-plane-induced anisotropy results in 90° rotations of the magnetic domains during magnetization and in the increase of magnetostriction for the thin film.