Influence of induced uniaxial anisotropy on the domain structure and phase transitions of yttrium-iron garnet films

The effect of induced uniaxial anisotropy on the properties and parameters of the domain structure and phase transitions in yttrium-iron garnet (YIG) films is investigated. Based on the measurements and the derived formulas we determine the difference between the magnetization and the uniaxial anisotropy field for each of the films. We have also measured the parameters of the domain structures and phase transitions of the films for the magnetization parallel and perpendicular to the projections of the [111] crystallographic axes onto the plane of the film. We find that films of pure YIG films grown in (111) are characterized by the existence of some critical value of the uniaxial anisotropy field. It is found that for films in which the uniaxial anisotropy field is larger than this critical value and films in which it is less than this critical value, such parameters of the domain structures as the ratio of the width of the domains to the film thickness, the orientation of the magnetization of the domains, the orientation of the domain boundaries, and the magnitudes of the phase transition fields differ substantially. Fiz. Tverd. Tela (St. Petersburg) 41, 2034–2041 (November 1999)     

Anisotropy of quasistatic magnetization-reversal processes in (210)-oriented iron-garnet films

An experimental study is made of the effect of an in-plane field H _p of various orientations on the domain structure and shape of the hysteresis loops of epitaxial iron garnet films with the (210) orientation. The characteristic of the magnetization reversal process (in fields somewhat lower than the anisotropy field) is taken to be the critical fields H _p1, H _p2, and H _p3, for which the magnetization reversal processes is interrupted at distinct stages. A method is proposed for constructing the phase diagram of the magnetic states of films, using measurements of the critical fields H _p for different amplitudes of the magnetization reversal field H _z . Two directions in the plane of the film are determined with an accuracy of a fraction of a degree from the hysteresis loops, where in the corresponding field Hp the transition from a single-domain state to a multidomain state occurs as a second-order phase transition. The characteristic changes in the shape of the hysteresis loop are consistent with the features in the reorganization of the domain structure of the (210) film. The preferential orientations of the stripe domain structure of the samples are determined relative to the crystal axes as determined by x-ray methods. Zh. Tekh. Fiz. 67, 32–35 (June 1997) Deceased     

Chaotic dynamics of interacting domain walls in uniaxial ferromagnetic films

The nonlinear dynamics of a periodic system of interacting domain walls in a thin ferromagnetic uniaxial film with transverse anisotropy is examined. The interaction between the domain walls takes place through the magnetostatic demagnifying fields of the domains. The equations of motion derived for such a system of walls are solved numerically by a 4–5th-order Runge-Kutta scheme, while the uniformity of the distributions of the phase trajectory, the form of the Poincaré cross section, and the spectral density of the vibrations serve as indicators of the type of oscillations. All the known types of oscillations are observed in a computer simulation of this nonlinear system: periodic, quasiperiodic, and chaotic. The computational results have a universal character for uniaxial, highly-anisotropic ferromagnetic films having a strip domain structure, since the results can be easily scaled for materials with different magnetic characteristics. Fiz. Tverd. Tela (St. Petersburg) 39, 2036–2039 (November 1997)     

钆钴非晶合金薄膜的电子衍射研究

用电子衍射方法研究了一些非晶钆钴合金磁性薄膜的结构,用Lorentz电子显微技术观察了其相应的磁结构。在所有薄膜的电子衍射图上均可清楚地看见七个弥散衍射环,其中两个最小的环分布在s<0.6?^-1(s=2sinθ/λ)的范围内。在不同的薄膜中观察到磁泡或平面畴结构。本文就这种由两种原子半径相差较大的元素,如稀土和过渡元素构成的非晶合金,讨论了如何只根据s<0.6?^-1范围内的衍射强度峰形,直接、定性地了解稀土与稀土原子、稀土与过渡族原子以及过渡族与过渡族原子之间最近邻配位数相对大小的问题。也讨论了钆钴薄膜相分离对磁各向异性的影响。 关键词：     

溅射钆钴合金薄膜的磁性

用射频溅射的方法制备得的钆钴膜具有垂直于膜面的单轴各向异性。电子衍射结果表明薄膜是非晶态的。电子探针分析证明钆和钴的“混合”是均匀的。用极向克尔效应观察了样品的磁畴,并测量了相应的磁滞迴线;发现在一定的工艺条件下,制备得的样品,在退磁状态呈现条状畴,并在一合适的外磁场作用下能转变为磁泡。     

The influence of strong bias voltage on the electrical and magnetic properties of the amorphous Gd-Co films

Some electrical and magnetic properties of Gd-Co films obtained by dc sputtering with bias voltage V_b are discussed. We observed a decrease in the compensation temperature and in the anomalous Hall resistivity with increasing bias voltage while the specific resistivity increases. The anisotropy constant, however, increases up to V_b = -200 V, where it reaches a maximum and then it decreases. Electrical conductivity of the films prepared with V_b greater than -100 V showed tunneling character. We conclude that not only resputtering of Gd atoms but also oxidation of Gd takes place during deposition when bias voltage is applied.     

Magnetically induced spin-rotation transition in iron-garnet films with canted-phase anisotropy

Epitaxial iron-garnet films exhibiting canted-phase and easy-plane anisotropies, with crystallographic (111) surface orientation are investigated by magnetooptical and inductive frequency methods. It is shown that four types of domain structure exist in the films. When the magnetization of the films is reversed by a static magnetic field oriented at various angles to the normal to the plane, anomalous behavior of the magnetic susceptibility is observed in the interval of magnetic-field orientation angles from 0.3° to 1.5°. Fiz. Tverd. Tela (St. Petersburg) 39, 1415–1420 (August 1997)     

Magnetic capacitance of the Gd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3</Subscript> thin films

The capacitance, inductance, and dissipation factor of the Gd _x Bi_1–x FeO₃ films were measured in the temperature range of 100 K < T < 800 K in magnetic fields of up to 8 kOe at frequencies of 0.1–100 kHz. The magnetic susceptibility maxima in the low-temperature region and dependences of the relaxation time and inductance on prehistory of the films cooled in zero and nonzero magnetic fields are established. The giant increase in magnetic capacitance in the external bias electric field is found. The results obtained are explained by the domain structure transformation in external electric and magnetic fields.     

Direct observation of magnetization reversal of epitaxial MnAs films

The magnetization reversal of MnAs epitaxial films on GaAs (0 0 1) substrates was investigated using a Kerr microscope. The direct observation of the change in domain structure under magnetic fields revealed characteristic magnetization reversal process of MnAs films with a ladder-type domain structure. The nucleus of the magnetization reversal region appears and propagates to neighboring α-MnAs lines, and then the ladder-type structures cover all over the surface. Finally the domain wall displacement occurs to expand the domain. The change in magnetic domain reflects the characteristic ridge/groove structures of MnAs films.     

Hysteresis of the characteristics of magnetostatic waves in ferrite films with stripe domains whose magnetization vectors are oriented close to the plane of the film

The propagation of zero-exchange spin waves (magnetostatic waves) is investigated in yttrium iron garnet films having a regular stripe domain structure with almost in-plane orientation of the domain magnetization vectors. The characteristics of the waves are studied for magnetizations of the film parallel and perpendicular to projections of the [111] crystallographic axes onto the plane of the film. It is established, in contrast with films having the domain magnetization vectors oriented close to the normal to the plane of the film, that both the propagation of magnetostatic waves and the variation of the parameters of the domain structure exhibit a distinctly pronounced hysteretic character as the magnetizing field is varied. The hysteresis of the amplitude-frequency response, equiphase, and dispersion curves of the magnetostatic waves is investigated. The authors examine how the hysteresis of these parameters is related to the hysteresis of the domain structure. The spectrum of magnetostatic waves is found to have an interval of wavelengths (wave numbers) that are not excited in the unsaturated film when the applied field is close to the saturation value, and this phenomenon as well exhibits hysteresis. Zh. éksp. Teor. Fiz. 114, 1430–1450 (October 1998)     

Thickness-dependent magnetic domain structures of Co ultra-thin film investigated by scanning transmission X-ray microscopy

Thickness-dependent magnetic domain structure of ultrathin Co wedge films (0.3 nm–1.0 nm) sandwiched by Pt layers was investigated by scanning transmission x-ray microscopy (STXM) employing X-ray magnetic circular dichroism (XMCD), utilizing elliptically polarized soft x-rays and electromagnetic fields, with a spatial resolution of 50 nm. The magnetic domain images measured at the Co L₃ edge showed the evolution of the magnetic domain structures from maze-like form to the bubble-like form as the perpendicular magnetic field was applied. The asymmetric domain expansion of a 500 nm-scale bubble domain was also measured when the in-plane and perpendicular external magnetic field were applied simultaneously.     

Magnetic force microscopy study of domain structures in magnetic films

Magnetic force microscopy is used to investigate two different types of samples: thin metal films and ferrite garnet films. It is pointed out for garnet films that magnetic force microscopy allows us only to judge the domain structure of surface layers. Problems associated with conducting measurements in external magnetic fields, the effect of the magnetic field of the probe on the investigated domain structure, and using magneto-polarized optics in combination with magnetic force microscopy are considered.     

Phase transitions in a domain wall of the four-sublattice antiferromagnet La2CuO4 in a magnetic field

The effect of an external magnetic field on the characteristics of domain walls was studied in a four-sublattice antiferromagnet La₂CuO₄. It was shown that a transition of domain-wall structure from one type into other types is possible for certain values of the fields. The critical fields of the transition were determined. The phase diagram of the stability of different types of domain walls was constructed. Fiz. Tverd. Tela (St. Petersburg) 40, 1510–1513 (August 1998)     

Generation of mesoscopic magnetic structures by local laser action

New effects are observed wherein the internal structure of the domain walls in a thin magnetic iron garnet film are modified by the action of focused laser radiation. A single laser pulse with increasing power gives rise to the following: 1) displacement of vertical Bloch lines in a domain wall; 2) generation of a pair of vertical Bloch lines on initially line-free walls; and, 3) an irreversible change in shape of a domain wall and the domain structure as a whole. The mechanism leading to the generation and displacement of Bloch lines is connected with the motion of domain walls which is induced by a local change in the distribution of demagnetizing fields as a result of a heating-induced decrease of the magnetization in the focal spot of the laser radiation. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 398–402 (25 September 1997)     

Field-induced phase transitions in magnetooptical films with a small positive anisotropy constant

We study phase transitions induced by a static magnetic field in magnetically uniaxial films with a small positive anisotropy constant. The phase diagram of these objects is determined in the H _∥-H _⊥ plane, where H _∥ and H _⊥ are, respectively, the components of the magnetizing field along and perpendicular to the surface normal. The stability boundary is located for all of the main types of domain configurations observed: a simple stripe domain structure, a stripe domain structure with periodic bending by surface distortions in the profile of the domain walls, and hexagonal lattices of cylindrical magnetic bubbles. Zh. éksp. Teor. Fiz. 111, 283–297 (January 1997)     

Ferroelectricity and structure of BaTiO3 grown on YBa 2Cu3O_{7 - \delta } thin films

We have investigated the crystal structure and the ferroelectric properties of BaTiO₃ thin films with YBa₂Cu₃O as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa₂Cu₃O and BaTiO₃ were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction. The ferroelectric behaviour of the BaTiO₃ films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm and a remanent polarisation of 1.25 μC/cm². At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indicates an interaction of domain walls with randomly distributed pinning centres. At a field of 5 MV/m we calculate a 3% contribution of the irreversible domain wall motion to the total dielectric constant. Received 24 June 1999 and Received in final form 27 August 1999     

Propagation of magnetostatic waves in unsaturated ferrite films with a strip domain structure

The propagation of surface and volume magnetostatic waves in unsaturated films of yttrium iron garnet is studied experimentally for the case when the wavelength greatly exceeds the domain width, while the domain width is comparable to the film thickness. The characteristics of these waves are examined for symmetric linear, asymmetric linear, and symmetric zigzag strip domain structures in the films. These characteristics cannot be explained by a theory based on averaging the magnetization over all the domains. Zh. éksp. Teor. Fiz. 111, 1016–1031 (March 1997)     

Rearrangement of the domain structure of single-crystal ferrite films in rotating magnetic fields

The behavior of the microband domain structure of films having pronounced crystallographic anisotropy is Investigated in rotating magnetic fields. In small fields, passing through the difficult axis, discontinuities are observed on the curves of mechanical moments which are associated with the reorientation of the magnetic moment by 90°. At the same time a new metastable transient domain phase appears in the form of wide bands stretched along the difficult axis.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 3#x2013;6, June, 1985.     

Static and dynamic properties of an isolated strip domain in a thin ferromagnetic film

A perturbation theory is developed for the integrodifferential Landau-Lifshits equation that describes the state of 2π-domain walls in ferromagnetic films. The static and dynamic parameters of a 2π-domain wall are determined, taking into account its micromagnetic structure. The limits of applicability of geometric domain wall models are indicated. Fiz. Tverd. Tela (St. Petersburg) 40, 269–273 (February 1998)     

Suszeptibilitätsmessungen an anisotropen Nickeleisen-Schichten

A d. c. field was applied along one of the anisotropy axes of evaporated nickel-iron films with uniaxial anisotropy, and a small a. c. field was applied perpendicular to the d. c. field. The magnetization amplitude parallel to the a. c. field was measured. The dependence of the susceptibility, measured like this, on the d. c. field strength corresponds to the single domain theory only for films with a smallH _c/H_K ratio or for large d. c. fields. The deviations from the single domain theory and the losses occurring can be explained by the ripple structure of the magnetization in polycrystalline films.