Possible identification of magnetostatic surface spin wave modes in ferromagnetic resonance on epitaxial yttrium—iron—garnet films

In ferromagnetic resonance experiments of yttrium—iron—garnet films, resonances have been observed whose characteristics are consistent with their interpretation as magnetostatic surface spin wave modes.     

Relation between relaxation losses in domain-wall motion and ferromagnetic resonance in garnet films

Domain-wall mobility has been studied in garnet films having perpendicular magnetic anisotropy and a narrow FMR line. An analysis of the obtained and published experimental data shows that for the value of the Landau-Lifshits reduced damping parameter derived from FMR measurements, Λ_FMR>2.4×10⁻⁹ Oe²·s, the domain-wall mobility is inversely proportional to Λ_FMR, which is in agreement with classical theory. For Λ_FMR<2.43×10⁻⁹ Oe²·s, the mobility decreases with decreasing Λ_FMR. Possible reasons for this behavior are discussed. An empirical expression relating the losses entailed in domain motion to FMR-related losses for small Λ_FMR is proposed. Fiz. Tverd. Tela (St. Petersburg) 40, 1519–1525 (August 1998)     

High-frequency susceptibility and ferromagnetic resonance in multidomain thin films of the yttrium-iron garnet type

The field dependence of the high-frequency susceptibility and the ferromagnetic resonance were experimentally studied in a thin (d≈0.1 µm) (111)-oriented single-crystal film of substituted yttrium-iron garnet with the factor q?1. It was shown that the anomaly in the high-frequency susceptibility observed in a magnetic field H parallel to the normal to the film surface in the magnetization saturation region (H≈H_s) has a dual nature; more specifically, this anomaly is associated with an abrupt collapse of the stripe domain structure and a ferromagnetic resonance in the experimental configuration H ∥ [111] and h ⊥ H. In this case, the film transition from the inhomogeneous multidomain state to the homogeneous (single-domain) state at the point H≈H_s has no indications of a second-order phase transition. The experimental frequency-field dependence of ferromagnetic resonance (FMR) in the sample under study, having a characteristic minimum at the point ω₀=5 MHz and H_FMR=H_s, agrees qualitatively and quantitatively with calculations. The influence of the cubic magnetic anisotropy and the film thickness on the FMR spectrum and the orientation of the spontaneous magnetization in domains with respect to the film plane in the zero field H was theoretically studied.     

Effect of dispersion of orthorhombic anisotropy fields on the ferromagnetic resonance linewidth in iron garnet films

The effect of the dispersion of anisotropy fields on the width of the ferromagnetic resonance line is calculated in films with orthorhombic anisotropy. The results of the calculation, based on a model of linear variation of the anisotropy fields with thickness and on the assumption of additivity of the different contributions to the resulting linewidth, are in good agreement with experimental results. Zh. Tekh. Fiz. 67, 131–134 (August 1997)     

Layered structure of epitaxial yttrium iron garnet films

The layered structure of yttrium iron garnet films, ranging in thickness from 0.7 to 4.1 μm, grown epitaxially on single-crystal gallium-gadolinium garnet substrates, was investigated by x-ray spectral microanalysis. The ferrite films were chemically etched layer by layer in a mixture of orthophosphoric and sulfuric acids at T=353–423 K. It was established that the chemical composition of the films varies over the thickness because of the nonuniform distribution of gadolinium, gallium, lead, and platinum ions; the film-substrate transitional layer and the surface layer of the film differ most greatly with respect to the composition and magnetic properties. It was shown that the thickness of the transitional layers and their negative effect on the magnetic characteristics of ferrite films decrease appreciably if at the time of immersion of the substrate and pulling of epitaxial structure out of the fluxed solution the substrate holder together with a special mixer rotate at a rate of 50 rpm and the pulling velocity is 20 cm/min. Zh. Tekh. Fiz. 69, 62–64 (December 1999)     

Wavelength modulation spectroscopy of epitaxial iron garnet films

Derivative absorption and reflectance spectra are reported for epitaxially grown iron garnet films and compared with derivative absorption results for bulk yttrium gallium garnet dilutely doped with Fe³⁺ Results are briefly discussed in terms of crystal field transitions, charge transfer excitons, and charge transfer bands all involving the iron 3d electrons.     

Exchange coupling in ultrathin epitaxial yttrium iron garnet films

Magnetic exchange coupling has been observed for ultrathin films of yttrium iron garnet (Y₃Fe₅O₁₂ or YIG). Single-crystalline YIG films were prepared on yttrium aluminium garnet (Y₃Al₅O₁₂ or YAG) substrates by pulsed laser deposition. (111) and (110) oriented substrates were used. Film thicknesses were varied from 180 ? to 4600 ?. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. Magnetic hysteresis loops recorded for ultrathin YIG films have a “bee-waist” shape and show a coupling between two different magnetic phases. The first phase is magnetically soft YIG. A composition study by secondary ion mass spectroscopy shows the second phase to be Y₃Fe_5-xAl_xO₁₂ due to the interdiffusion of Fe and Al at the film/substrate interface. This compound is known to be magnetically harder and to have weaker magnetization than YIG. The coupling of the two phases leads to a hysteresis loop displacement at low temperatures. This displacement varies differently with film thickness for two substrate orientations. Assuming an interfacial coupling, the maximal interaction energy is estimated to be about 0.17 erg/cm² at 5 K for (111) oriented sample. Received 3 June 2002 / Received in final form 7 October 2002 Published online 27 January 2003 RID="a" ID="a"Presently at LPM, Université H. Poincaré, BP 239, 54506 Vandœuvre-lès-Nancy e-mail: popova@lpm.u-nancy.fr     

Linewidth of ferromagnetic resonance in holmium yttrium garnet ferrites

The specific features experimentally observed in the behavior of the linewidth of ferromagnetic resonance in holmium yttrium garnet ferrites were investigated as a function of the orientation of the external magnetic field at low temperatures. The analysis was performed using the model spectrum of holmium ions, according to which the ground state of these ions is represented by two closely spaced levels (quasi-doublet) that are sufficiently far removed from the other levels. A comparison of the theoretical results with the experimental data was carried out.     

Investigation of the photothermally modulated ferromagnetic resonance signal from magnetostatic modes in yttrium iron garnet films

The conventional and photothermally modulated (PM) ferromagnetic resonance (FMR) of magnetostatic modes (MSM) in yttrium iron garnet (YIG) films have been investigated as a function of temperature. Approaching the ferrimagnetic transition at T _c=560 K a strong enhancement of the PM-FMR signal amplitude is observed which is accompanied by a change of the signal shape. The observations are discussed in the framework of a model that takes into account the temperature derivatives of those quantities that contribute to the high-frequency susceptibility. At temperatures still below T _c a paramagnetic line emerges. The MSM disappear in a state of finite magnetization which is explained on the basis of damping of the MSM being important in the vicinity of the magnetic phase transition. Additionally, frequency and power dependent measurements are presented and the imaging ability of PM-FMR is demonstrated.     

Localized ferromagnetic resonance in inhomogeneous thin films

The effect of sample inhomogeneity on the ferromagnetic resonance linewidth is determined by diagonalization of a spin wave Hamiltonian for ferromagnetic thin films with inhomogeneities spanning a wide range of characteristic length scales. A model inhomogeneity is used that consists of size D grains and an anisotropy field H(p) that varies randomly from grain to grain in a film with thickness d and magnetization M(s). The resulting linewidth agrees well with the two-magnon model for small inhomogeneity, H(p)DpiM(s)d, the precession becomes localized and the spectrum approaches that of local precession on independent grains.     

X-ray detected ferromagnetic resonance in thin films

We discuss the physical content of X-ray Detected Magnetic Resonance (XDMR), i.e. a novel spectroscopy which uses XMCD to probe the resonant precession of the local magnetization in a strong microwave pump field. We focus on the simplest case of a steady-state precession of elemental moments in the non-linear regime of angular foldover. Like XMCD, XDMR is element and edge selective and could become a unique tool to investigate how precessional dynamics can locally affect the spin and orbital magnetization of p- or d-projected DOS. This should be possible only in the limit where there is no overdamping due to ultrafast orbit-lattice relaxation.     

Elastically driven ferromagnetic resonance in nickel thin films

Surface acoustic waves (SAWs) in the GHz frequency range are exploited for the all-elastic excitation and detection of ferromagnetic resonance (FMR) in a ferromagnetic-ferroelectric (Ni/LiNbO(3)) hybrid device. We measure the SAW magnetotransmission at room temperature as a function of frequency, external magnetic field magnitude, and orientation. Our data are well described by a modified Landau-Lifshitz-Gilbert approach, in which a virtual, strain-induced tickle field drives the magnetization precession. This causes a distinct magnetic field orientation dependence of elastically driven FMR that we observe in both model and experiment.     

Deposition and characterization of diamond epitaxial thin films on silicon substrates

Heteroepitaxial diamond growth has been attempted on mirror-polished monocrystalline (001), (111), and (110) silicon substrates by microwave plasma CVD. The surface morphology and the crystallographic properties of the films were characterized by means of Scanning Electron Microscopy (SEM), Raman spectroscopy, X-ray diffraction, and X-ray and Raman pole-figure analysis. The results demonstrate epitaxial growth of diamond on both (001) and (111) oriented silicon substrates. Preliminary results give strong evidence for substrate-induced orientation of the diamond crystallites also on (110) oriented silicon substrate. The heteroepitaxy can be assigned to the oriented covalent bonding across the interface between diamond and silicon.     

Nuclear magnetic resonance study of epitaxial Co layers on single-crystal substrates

Nuclear magnetic resonance (NMR) is a powerful tool to study the local structure of ultrathin magnetic films and multilayers. This is demonstrated with an NMR study of ultrathin molecular beam epitaxy-grown Co layers on single-crystal Cu(111), Cu(110) and Pd(111) substrates. Co on Cu(111) results in a mixture of fcc and hep phases and the Cu(111)/Co interface is near to perfect. Co on Cu(110) grows mainly fcc in long stripe-shaped islands with rough Co/Cu interfaces. Finally, Co on Pd(111) gives a (111)-oriented fcc structure. The top surface is flat, but the Pd(111)/Co surface is intermixed.     

Luminescence of gadolinium gallium garnet epitaxial films under excitation by synchrotron radiation

The luminescence excited by synchrotron radiation in gadolinium gallium garnet single-crystal films grown by liquid-phase epitaxy from lead-and bismuth-containing solution melts on Gd₃Ga₅O₁₂ substrates is investigated. It is shown that the luminescence intensity in the visible range of the spectrum depends on the type and concentration of impurity ions passing from the solvent into the film.     

Ferromagnetic resonance in epitaxial films of uniaxial barium hexaferrites

The magnetic parameters of epitaxial barium hexaferrite films are studied. The hysteresis of the field and frequency dependences of ferromagnetic resonance in the films is investigated in the ranges of the multidomain-monodomain and monodomain-multidomain transitions. The effect of the substrate thickness on film-microwave field interaction is examined.     

Growth and characterization of ferromagnetic MnAs films on different semiconductor substrates

MnAs thin films were grown by metalorganic vapour-phase epitaxy (MOVPE) on GaAs(0 0 1), Si(0 0 1) and oxidised silicon substrates. All films are crystalline and contain only the ferromagnetic α-MnAs phase. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements show that films on GaAs(0 0 1) have strong preferential orientation, developing elongated grains parallel to [1 –1 0] GaAs while films on bare and oxidised Si are polycrystalline with irregular-shaped, randomly oriented grains. Magneto-optic Kerr effect (MOKE) measurements show good magnetic properties for films on GaAs, such as strong in-plane anisotropy and squareness of the hysteresis loop in the easy direction. A Curie temperature of 340 K, remarkably higher than the bulk material (315 K), was found for a 65 nm thick film on GaAs. Films grown on bare and oxidised silicon wafers had lower Curie temperature and were magnetically isotropic.     

Optical harmonic generation in magnetic garnet epitaxial films near the fundamental absorption edge

Spectra of the second and third optical harmonics generated in epitaxial films of magnetic garnets were studied in the ranges 1.7–3.2 and 2.4–4.2 eV, respectively. A large magnetic contrast was revealed in second-optical-harmonic spectra, which reaches 100% at certain photon energies. By contrast, the symmetry-allowed magnetic contribution to spectra of the third optical harmonic was not found. While linear absorption in ferrite-garnet films grows by two orders of magnitude above the fundamental absorption edge at ～3.2 eV, the intensity of nonlinear spectra did not reveal any noticeable increase over this spectral range.