Measurements of Hk and Ms in thin magnetic films by the angular dependence of the planar Hall effect

It is shown that the angular dependences of the planar Hall effect measured with infinite magnetic field and with magnetic field H⩾H_k have an intersection point and this fact is enough for measuring the anisotropy field H_k applying the method presented by Pastor, Ferreiro and Torres in J. Magn. Magn. Mat. 53 (1986) 349, 62 (1986) 101. The scaling of the Hall tension U proportional to M²_s in mV/Am^-1 gives a possibility for calculating the M_s-values of the films. These assumptions are verified for NiFe- and NiFeGe films with a uniaxial magnetic anisotropy.     

Classical dependence of the domain wall velocity on the magnetic field in garnet ferrite films with orthorhombic magnetic anisotropy

The dependence of the domain wall velocity V on the acting magnetic field H is investigated for bismuth-containing single-crystal garnet ferrite films with orthorhombic magnetic anisotropy. It is shown that this dependence includes both the initial linear portion and a saturation portion and exhibits a complex behavior. This behavior is explained within the model of domain wall motion with spin wave radiation.     

Nonlinear oscillations of magnetization accompanying pulsed 90°-magnetization of garnet ferrite films with easy-plane anisotropy

Abstract Nonlinear oscillations of magnetization (with a fundamental harmonic frequency of ≈0.5 GHz) emerging during 90°-pulsed magnetization of garnet ferrite films with easy-plane anisotropy are studied. Analysis of longitudinal and transverse magnetization signals and of the magnetization vector hodograph plotted on their basis shows that the weak dependence of the oscillation intensity on duration t _f of the magnetizing magnetic field pulse (upon its variation from 0.4 to 6–8 ns), which is typical of these films, can be explained by the presence of biaxial anisotropy in the plane of actual films.     

The initial stage in the nonlinear motion of a domain wall in garnet films

A study of the domain-wall motion in single-crystal garnet films of the YBiFeGa system with a perpendicular magnetic anisotropy, activated by a constant in-plane bias field H _p parallel to the wall plane and a pulsed drive field H _g of an amplitude corresponding to the nonlinear region of the domain-wall velocity vs. the H _g relation is reported. The earlier data suggesting the existence of an initial phase of motion, where the wall is accelerated to a high instantaneous velocity, have been confirmed. The wall behavior in the initial phase has been shown to be affected by the field H _p and the drive-field pulse rise time. A possible mechanism of the wall structure transformation after the application of the H _g pulse is considered. It has been established that the dependence of the wall velocity on H _p in the saturation region disagrees with theory.     

High rotatable magnetic anisotropy in MnBi thin films

The variations of the structural and magnetic properties of Bi/Mn/Bi and Mn/Bi/Mn trilayer film systems of equiatomic composition in the process of vacuum annealing are studied. The annealing of Bi/Mn/Bi films at a temperature of 270°C for an hour results in the synthesis of the well-studied highly oriented low-temperature LT-MnBi(001) phase with the perpendicular magnetic anisotropy K _u ～ 1.1 × 10⁷ erg/cm³ and coercivity H _C ～ 1.5 kOe. In contrast to Bi/Mn/Bi, polycrystalline LT-MnBi nanoclusters are formed in Mn/Bi/Mn films under the same annealing conditions. A high rotatable magnetic anisotropy exceeding the shape anisotropy is detected in the films under consideration: the easy axis of anisotropy with the inclusion of the delay angle in magnetic fields above the coercivity H > H _C = 9.0 kOe can be oriented in any spatial direction. It is shown that the nature of rotatable magnetic anisotropy is due to the structural coexistence of epitaxially coupled LT-MnBi and QHTP-Mn_1.08Bi phases. The reported experimental results indicate the existence of a new class of ferromagnetic film media with the spatially tunable easy axis.     

Dynamics of domain walls in bismuth-ytterbium-containing garnet ferrite films in the vicinity of the angular momentum compensation point

The dependence of the domain-wall velocity V on the acting magnetic field H is investigated for (Bi,Yb)₃(Fe,Ga)₅O₁₂ garnet ferrite single-crystal films in the vicinity of the angular momentum compensation point at different temperatures. The films are grown by liquid-phase epitaxy from a supercooled solution melt on Cd₃Ga₅O₁₂ substrates with the (111) orientation. It is demonstrated that, in these films, the precessional mechanism is not responsible for the motion of domain walls but there arises an internal effective magnetic field that weakens the acting magnetic field.     

Effect of thermal process on magnetic anisotropy in FeCoB soft underlayer

Relationship between magnetic anisotropy field H_k and thermal processes during the preparation has been studied for FeCoB thin films. The FeCoB films deposited on the glass substrates by facing targets sputtering successfully showed strong magnetic anisotropy when the substrate was heated at the substrate temperature T_s above 100 °C. Additionally, the lattice spacing of FeCo(1 1 0) in the perpendicular direction was found to decrease depending on the substrate temperature T_s. Among various temperature histories, the heating processes with a phase of increasing T_s revealed the further improvement of H_k. Meanwhile, high H_k in the films disappears after the post-deposition annealing at the temperature above 400 °C.     

Improvement of magnetic properties and read/write characteristics in SmCo5 perpendicular thin films

An SmCo₅ alloy is a promising candidate for ultra-high density magnetic recording media because of its strong uniaxial magnetocrystalline anisotropy, whose constant, K_u, is more than 1.1×10⁸ erg/cm³. Recently, we successfully obtained high perpendicular magnetic anisotropy for a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, it is necessary to improve magnetic properties and read/write (R/W) characteristics for applying SmCo₅ thin films to perpendicular magnetic recording media. In this study, we focused on reduction of magnetic domain size and change of a magnetization reversal process of SmCo₅ perpendicular magnetic thin films by introducing carbon (C) atoms into the constituent Cu underlayer. The magnetic domain size became small and the ratio of coercivity (H_c) against magnetic anisotropy (H_k) which is an index of the magnetization reversal process was increased by adding C atoms. We also evaluated the R/W characteristics of SmCo₅ double-layered media including C atoms. The medium noise was decreased and signal-to-noise ratio increased by introducing the C. The addition of C into the Cu underlayer is effective for changing the magnetization reversal process, reducing medium noise and increasing SNR.     

Complete magnetizing field relating with magnetization reversal dynamics

We report the experimental finding that a complete magnetizing field H_M exists in magnetization reversal dynamics of ferromagnetic thin films, which is much larger than the apparent magnetic saturation field measured from the major hysteresis loop. Magnetization reversal dynamics contrastingly changes from nucleation dominated to wall-motion dominated according to an initial magnetization state magnetized by a field below H_M, whereas it is basically unchanged when the field is larger than H_M. The complete magnetizing field is found to be 1.5–2.0 times larger than the apparent magnetic saturation field and 6–10 times smaller than the anisotropy field in Co/Pd multilayer thin films.     

Investigation of structural and magnetic properties of Ni, NiFe and NiFe2O4 thin films

Soft magnetic thin films of Ni, NiFe and NiFe₂O₄ were prepared using reactive magnetron sputtering in various deposition conditions. Experimentally observed soft magnetic property was compared and correlated with nanocrystalline structure evolution. Ni and NiFe deposited films are textured with fcc(111) phase preferred orientation. Accordingly, grain size and lattice parameter were calculated from X-ray diffraction (111) peak line width and 2θ peak position. Addition of reactive gas oxygen in deposition process has substantial effect on crystalline structure of film. There is phase transition from the ordered NiFe (111) structure to the NiFe₂O₄ nanocrystalline phase. The resulting film has shown small X-ray diffraction intensity peak corresponding to (311) and (400) orientation, indicating small amount of existing NiFe₂O₄ phase. The mechanism has been discussed to be responsible for nanocrystallization and amorphization of NiFe₂O₄ films. Magnetic measurement (M-H) loop reveal soft magnetic nature of films with magnetic anisotropy. The coercivity (H_c) of films is in accordance with random anisotropy model, where H_c reduced with grain size. The structural transformation was supported by Fourier transforms infrared spectroscopy measurement. The films are highly smooth with surface roughness in the range of ∼0.53-0.93 nm. NiFe₂O₄ films have shown lowest surface roughness with highest electrical resistivity values. The structural, surface, magnetic and infrared spectroscopy results are observed and analyzed.     

The annealing effect and the origin of perpendicular anisotropy in amorphous GdTbFe film

The effect of annealing on the magnetic anisotropy and the thermal stability has been investigated for an amorphous Gd₂₇Tb₁₀Fe₆₃ film prepared by magnetron sputtering. On the basis of a pseudodipolar interaction, a numerical computation is performed primarily on fitting a variance of the anisotropy constant with that of the thermal annealing at various temperatures and shows that a contribution from Tb-Fe pairs are dominant in determining the perpendicular anisotropy. H_c = K_u/M_s is used to describe the variance of coercivity after that heat treatment. The behaviour of annealing the films in air shows that the films with a protective Al film possess a good thermal stability for magneto-optical recording.     

Magnetic properties of metastable Gd-Cr alloys

We report on the magnetization, magnetocaloric effect, magnetic ordering temperatures, saturation magnetic moments and anisotropy of sputter-deposited Gd_xCr_1−x alloys with Gd atomic concentrations, x, ranging from 0.13 to 0.52. The complex magnetic nature of the Gd-Cr films was revealed from the M×H isotherms, which do not show saturation even at an applied field of 70 kOe and a temperature of 2 K and do not exhibit a linear behavior at higher temperatures. For some of the samples, the isotherms were used to determine the isothermal entropy variation as a function of temperature, for a change of 50 kOe in the applied magnetic field. The saturation magnetic moment varies with x and follows the dilution law, implying that the Cr atoms do not contribute to the total moment of the Gd-Cr alloys. Both static magnetization and dynamic susceptibility measurements reveal the existence of a magnetic glassy behavior in the alloys, which occurs below a freezing temperature. The existence of anisotropy at low temperatures for all samples was revealed by their M×H hysteresis loops from which the in-plane coercive fields, H_c, were determined. A monotonical increase in H_c with increasing Gd concentration was observed.     

Nonmonotonic magnetic-field dependence of transport coefficients for n-Bi-Sb semiconducting alloys

The transport coefficients of tellurium-doped n-Bi_{1 ? x} Sb _x semiconducting alloys (0.07 ≤ x ≤ 0.15) are studied for single-crystal samples in the temperature range 1.5 ≤ T ≤ 40 K and in magnetic fields 0 ≤ H < 20 kOe. The theory developed in this study attributes the specific features in the behavior of the transport coefficients observed in a magnetic field to a strong anisotropy of the electron spectrum and anisotropy in the electron relaxation time. It is found that the dependences of the transport coefficients on the magnetic field for H ∥ C ₃ can be theoretically expressed through one anisotropy parameter δ, and those for H ∥ C ₂, by means of several anisotropy parameters, namely, γ, η, ζ, and m ₃/m ₁. It is established that the anisotropy parameter δ in the n-Bi-Sb semiconducting alloys can be estimated from measurements of the electrical resistivity ρ₂₂(∞)/ρ₂₂(0) ? δ and the Hall coefficient R _12.3(∞)/R _12.3(H → 0) ? δ in a magnetic field H ∥ C ₃. It is shown that the observed increase in the thermoelectric efficiency by a factor of 1.5–2.0 in the transverse magnetic fields H ∥ C ₃ and H ∥ C ₂ originates from the nonmonotonic dependence of the diffusion component of the thermopower Δα₂₂(H)(?T ∥ C ₁) on the magnetic field. The nonmonotonic dependence of the diffusion thermopower in n-Bi-Sb semiconducting alloys is associated with the strong anisotropy of the electron spectrum, the anisotropy in the electron relaxation time, and the many-valley pattern of the spectrum.     

Soft magnetic properties of FeCo films with Co underlayer

Bilayered Fe₆₅Co₃₅ (=FeCo)/Co films were prepared by facing targets sputtering with 4πM_s∼24 kg. The soft magnetic properties of FeCo films were induced by a Co underlayer. H_c decreased rapidly when the Co underlayer was 2 nm or more. The films showed well-defined in-plane uniaxial anisotropy with the typical values of H_ce=10 Oe and H_ch=3 Oe, respectively. High frequency characteristics of the films show the films can work at 0.8 GHz with real permeability as high as 250.     

Magnetic transitions in K2MnCl4·2H2O

Results of (dM/dH) measurements on tetrahedral K₂MnCl₄·2H₂O as a function of temperature and magnetic field, are presented. An antiferromagnetic transition along the tetragonal axis is observed at T_N = (3.05±0.05) K. The H-T magnetic phase diagram was completely determined, and shows the usual characteristics of that of a low anisotropy antiferromagnet. The T = 0 critical fields are compatible with the values H_E = (29.2±0.3) kOe and H_A = (5.9±0.6) kOe for the exchange and anisotropy fields.     

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     

On the relation between the effective ferromagnetic resonance linewidth Δfeff and damping parameter αeff in ferromagnetic Fe-Co-Hf-N nanocomposite films

Ferromagnetic Fe-Co-Hf-N nanocomposite films were investigated concerning their microstructure-dependent frequency behaviour. To modify the composition, the films were deposited by reactive RF magnetron sputtering by using three different 6 in. targets with various Hf fractions. The films were post-annealed up to 600 °C in a static magnetic field to induce an in-plane uniaxial anisotropy and to obtain different crystal sizes. Depending on the annealing temperature, high-frequency losses were investigated by considering the full-width at half-maximum (FWHM) Δf_eff of the imaginary part of the frequency-dependent permeability which showed a resonance frequency f_FMR of 2.3 GHz for an in-plane uniaxial anisotropy field H_u of 4 mT. The FWHM in correlation with the damping parameter α_eff is discussed, e.g., in terms of two-magnon scattering. Damping occurs due to film inhomogeneity in magnetisation and uniaxial anisotropy caused by a magnetocrystalline anisotropy H_a and/or non-magnetic phases. This will result in homogenous or even inhomogeneous resonance line broadening if additional and resonance as well as precession frequencies of independent grains arise.     

Phase transitions in biperiodic stripe domain structures of uniaxial magnetic films with a positive anisotropy constant

New phase transitions induced by a magnetic field and accompanied by a change in the symmetry or the period of the distribution of the magnetization vector are observed in biperiodic stripe domain structures of iron garnet films with a positive anisotropy constant. A symmetry classification of the observed types of domain structures is derived, and the form of the state diagram of the films is determined in the H∥H⊥ plane, where H∥ and H⊥ are the components of the magnetic field vector perpendicular and parallel to the normal to the surface. Zh. éksp. Teor. Fiz. 114, 2089–2110 (December 1998)     

Anisotropic properties of the microwave magneto-dissipation in high-T c superconducting films

We report measurements of the magnetic field dependent microwave dissipation at 21 GHz in Bi₂Sr₂CaCu₂O_8+x epitaxial films and in oriented YBa₂Cu₃O_7?σ films, by means of the end-wall-replacement cavity technique. The power reflected by the tuned cavity is measured as a function of the external magnetic fieldH and of the angle ε betweenH and the (a, b), planes, at fixed temperatures. In Bi₂Sr₂CaCu₂O_8+x , apart from a narrow (Δε≈0.5°) angular range close to the parallel orientation, the strongly anisotropic dissipation exhibits striking scaling properties: all the data at fixed temperature can be made to collapse on a single curve with a simple angular scaling of the magnetic field:H→H/f(ε). It is found that the anisotropy ratiof(0°)/f(90°) increases with temperature. It is shown that the scaling functionf(ε) and its temperature evolution are in agreement with the model for a quasi-2D superconductor. In YBa₂Cu₃O_7-σ the presence of the flux-flow dissipation prevents the application of a scaling procedure, and a specific model must be applied. We obtain that the anisotropy is almost constant with the temperature, as predicted for a three-dimensional, anisotropic superconductor.     

Effect of the morphology on the mechanisms of the magnetization reversal of multilayered thin Co/Pd films

A comparative study of the magnetization curves of continuous and porous multilayered Pd_10nm/[Co_0.3nm]/Pd_0.55nm]15/Pd_2nm films deposited on an anodized TiO₂ template was performed by magnetometry. Based on the comparison of the dependences of coercive field H_C on angle θ between the easy-magnetization axis and the direction of external magnetic field H with theoretical dependences H_C(θ) for the magnetization reversal by domain walls motion (according to the Kondorski model) and the rotation of magnetic moments (by the Stoner–Wohlfarth model), the differences in the mechanisms of magnetization reversal for two mentioned types of the films were revealed. The correlation between the difference in the morphologies of the continuous and porous films and revealed change in the mechanisms of the magnetization reversal, as well as the changes in values of H_C and calculated constants of the magnetic anisotropy, is discussed.