V. Cagan

Temperature dependence of the domain wall mobility in YIG, deduced from the frequency spectra of the initial susceptibility of polycrystals

Abstract The Dorings equation of motion of a 180°-domain wall, when adapted to the case of pinned domain walls as in polycrystalline materials, leads to a 1 / D 2 dependence of the relaxation frequency of domain walls, which has already been observed. Mobility and damping parameters can then be deduced from the frequency spectrum of initial susceptibility. The domain wall mobility value obtained by using such a method on polycrystalline YIG samples at RT (1500 cm/s Oe) agrees with recent determinations (2000 to 3000 cm/s Oe) which use pulse field measurements on picture frame single crystals or optical measurements on thin films. The method is applied for temperature measurements; a proportionality between the experimental and the theoretical temperature dependence of the damping parameter and the mobility is obtained from RT up to T c , which is discussed taking into account the different parameters involved.

Ferrimagnetic thin films prepared by pulsed laser deposition

Abstract Thin films, with thickness ranging from 25 nm up to 1.5 μm, of well-known ferrimagnetic materials such as NiFe2O4, CoFe2O4, Ni0.5Zn0.5Fe2O4, and BaFe12O19 have been prepared by PLD. Films made at low substrate temperature (T

Preparation and some properties of pulsed laser deposited YFeO3 films

Abstract YFeO 3 orthoferrite films have been deposited on to quartz and sapphire substrates by pulsed laser deposition. The films crystallize when annealed at temperatures in the range 750 to 900°C. The perpendicular hysteresis loops are rectangular with a maximum coercivity of 9 kOe. The Faraday rotation at 633 nm wavelength is in the range 4–5 × 10 3 deg/cm.

Microstructure and magnetic properties of spinel and hexagonal ferrimagnetic films prepared by pulsed laser deposition

Abstract Thin films of NiFe 2 O 4 , CoFe 2 O 4 , Ni 0.5 Zn 0.5 Fe 2 O 4 , and BaFe 12 O 19 , deposited at temperatures higher than 500°C are isotropic and polycrystalline, the thickness (25 nm up to 1.5 μm), the grain size (50 nm to 1 μm) and surface roughness (1 to 100 nm) depending upon deposition parameters. Saturation magnetizations are close to the bulk values, but coercivities are rather high: up to 500 Oe for Ni-ferrites and more than 3 kOe for the hexaferrite.

Does the magnetostriction control the acoustic emission

Abstract It is shown that the acoustic emission (AE) activity in polycrystalline YIG:Mn and Ni-Zn ferrites is proportional to the hysteresis losses, and increases with grain size, but cannot be related to the magnetostriction λ s contrary to the current theory of AE. Our interpretation attributes AE to the domain wall creation/annihilation process.

Magnetic studies of Co/Ag multilayers

Abstract Co/Ag multilayers have been prepared by evaporation in UHV. For a Co layer thickness below about 2 nm some increase in the magnetization above that of the bulk and a strong uniaxial anisotropy are observed. The latter is considered to be of surface origin.

Domain wall mobility of some polycrystalline ferrimagnets: experimental results versus classical theory

Abstract The domain wall mobility of three compounds (Y 3 Fe 5 O 12 , Gd 3 Fe 5 O 12 , Ni 0.47 Zn 0.53 Fe 2 O 4 is determined from initial permeability spectroscopy of polycrystals. The observed mobility values, nearly composition independent (typically 2300 cm/s Oe ± 30% at 400 K) appear to be not related to the FMR linewidth, i.e. the spin damping parameter, but are strongly dependent on the wall thickness.

Natural spin resonance (with various domain wall orientations) in mixed garnets Y3−xGdxFe5O12

Abstract Natural spin resonances (NSR) well separated from the domain wall relaxation are presented in YGdIG samples. It is shown that even in dynamical conditions the complementary term to K 1 in the total anisotropy cannot be explained by the dipolar energy. The natural stress value is found to be of the order of 10 9 dyn cm -2 . Experiments with applied dc fields confirm the gyromagnetic nature of NSR.

Magnetoelastic and total anisotropy effects on the domain-wall dynamics in the polycrystalline state

This work investigates the domain-wall (DW) mobility due to magnetoelastic interaction. Polycrystalline samples with high grain-size homogeneity were prepared based on the general formula Y3Fe5-xMnxO12 (0 < x < 0.28). A series of samples was especially selected where the longitudinal magnetostriction changed from −2.14 × 10−6 to +7.65 × 10−6 at 300 K, while the single-crystal crystalline anisotropy constant K1 remained negative. The effects of the magnetostriction and the total anisotropy K on the complex magnetic permeability spectrum μ∗(f) were investigated in a broad frequency range (0.3–3 GHz). Two characteristic regions of variation of the real (μ′) and the imaginary (μ″) parts of the complex permeability as functions of λs were established. Near λs = 0, a resonance-type spectrum was observed. The model of ‘diametrical spherical DW’ is inapplicable for λs ⪢ 0 - the DW dynamics is then influenced exclusively by the stress anisotropy and by the strong isotropic exchange stress arising from the anisotropic magnetostrictive deformation constrained by the neighboring grains. The significant decrease of the initial permeability in this region can be explained by the rise in the concentration of DW not having a 180° orientation.

Magnetic and magneto-optical studies in Fe/AlN multilayers

We have prepared Fe/AlN multilayers by rf sputtering using water-cooled glass substrates and studied their properties. For t(Fe) > 30 A the magnetization remains at the bulk value of 1710 G. For t(Fe) = 10 A it decreases to 550 G. The coercivity shows a broad minimum of 4 to 5 Oe for 60 A < t(Fe) < 100 A. The specific Faraday rotation shows a broad peak near t(Fe) = 40 A but falls for thinner Fe layers. The polar Kerr rotation shows a plateau but decreases sharply below 36 A.