BaFe12−xGaxO19 (x ≤ 1.2) hexaferrites were synthesized via the usual ceramic technology. It has been established that with an increase in x, the unit cell and magnetic parameters monotonically decrease. The frequency of natural ferromagnetic resonance firstly decreases from 49.6 GHz down to 49.1 GHz when x = 0.6, and then it increases up to 50.5 GHz. The line width monotonically increases from 3.5 GHz up to 5 GHz. The peak amplitude of the resonant curve changes slightly with the exception of when x = 0.9, when it reaches −16 dB. The 1.3 GHz kOe−1 frequency shift in the bias field is more intensive for small values, when x = 0.3. The decreasing values of the magnetic parameters are a result of the dilution of Fe3+–O2−–Fe3+ superexchange interactions. The behavior of the amplitude-frequency characteristics is largely determined through the reduction of uniaxial exchange anisotropy. The prospects of Ga-substituted hexaferrites acting as a material that effectively absorbs the high-frequency electromagnetic radiation are shown.

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Investigation into the structural features and microwave absorption of doped barium hexaferrites

An investigation of the magnetic anisotropy change in BaFe12−2xTixCoxO19 single crystals

Effect of gallium doping on electromagnetic properties of barium hexaferrite

We demonstrate low ferromagnetic resonance (FMR) linewidths and high remanence magnetization in polycrystalline M-type Sc-doped Ba ferrites having anisotropy fields of ∼8 kOe and perpendicular orientation of the spontaneous magnetization vector. This is a result of applying a unique processing technique that makes use of a polymer network-assisted alignment of hexaferrite particles in high magnetic fields. The resulting compacts exhibit high squareness (M r /M s ∼92%) and low FMR linewidths (∼530 Oe) at X-band and Ka-band. This represents an ∼ 74% decrease in linewidth compared with previous reports for polycrystalline BaM ferrites using conventional processes. We also have detailed origins of the FMR linewidth broadenings in terms of some important theoretical models. These materials have potential for use in low frequency self-biased microwave/ millimeter devices such as circulators and isolators.

Perpendicularly Oriented Polycrystalline BaFe11.1Sc0.9O19 Hexaferrite with Narrow FMR Linewidths

Effects of Bi2O3 on FMR linewidth and microwave dielectric properties of LiZnMn ferrite

Anisotropy fields and FMR linewidth in single-crystal Al, Ga and Sc substituted hexagonal ferrites with M structure

The FMR linewidth of the 210-, 110-and 220-magnetostatic modes in a highly polished and annealed polycrystalline YIG sphere have been measured as a function of frequency at different temperatures. From these results a separation into anisotropy and porosity induced line broadening contributions was accomplished. The results show that both line broadening contributions arise mainly from scattering to low and medium k states of the spinwave manifold. Excellent quantitative agreement was found with Schlomann's anisotropy broadening theory over the whole range of the spinwave manifold covered by the investigated modes. The obtained porosity broadening contribution contradicts the theoretical predictions using the density of spinwave states as a scattering reservoir. A qualitative explanation of this result can be given by taking into account the dispersion of the spinwave angle Θ 0 .

Separation of anisotropy and porosity contributions to inhomogeneous broadened FMR linewidth in polycrystalline YIG

The cation distribution in Ga, Al and Sc substituted YIG has been determined from 4\piM_{s} measurements at 295K and 77K of annealed and quenched spheres made from single crystals. The effects of thermal treatment on 4\piM_{s} show quantitatively agreement with calculations from the molecular field theory and Borghese's thermodynamic equilibrium expression. The stabilization energies describing quantitatively the lattice site preference of the substituted cations have been determined to: E_{s} = 0.246 \pm 0.01 eV for Ga, E_{s} = 0.15 \pm 0.02 eV for Al and E_{s} = -0.35 \pm 0.03 eV for Sc. The observed kinetics of the cation transfer strongly depend on the temperature, the kind of cation substituted and on the defect concentration. Annealing in inert and reducing atmosphere decreases the relaxation rate of the redistribution by several orders of magnitude. FMR linewidth data indicate the creation of Fe2+which is known to enhance rigorously the cation transfer.

Annealing effects on cation distribution in diamagnetically substituted single crystal Yttrium Iron Garnet

Results of the FMR linewidth versus frequency and temperature and of the parallel pump spinwave linewidth are reported for YIG and Ga:YIG single crystal spheres subjected to different thermal treatments in O 2 , N 2 and H 2 /N 2 ambients. The slopes of the frequency dependent part of the FMR linewidth are found to be proportional to the respective measured spinwave linewidth, w hence either of these quantities represents the intrinsic FMR losses of the bulk material. The observed frequency independent park of the linewidth is assumed to represent two-magnon scattering contributions due to surface and crystal imperfections. This contribution has been further separated into two parts which depend on the anisotropy field and the saturation magnetization, respectively. The intrinsic FMR losses and the two-magnon scattering contribution are characteristically influenced by changes in the cation distribution, saturation magnetization, anisotropy field and oxygen vacancy concentration induced in the samples by the various thermal treatments.

Annealing effects on FMR linewidth in Ga substituted YIG

The intrinsic loss properties of the ferromagnetic resonance (FHR) in Ga, Al, Sc and V substituted iron garnets have been investigated at different temperatures from T=77 K up to the Curie temperature by FHR measurements as a function of frequency. After separation of masking two-magnon scattering contributions the intrinsic losses of the bulk single crystal materials were resolved in terms of the dimensionless Landau-Lifshitz damping parameter α f . The results of α f (T) obtained for different temperatures were found to increase linearly versus 1/4\piM_{s} (T), the reciprocal of the respective saturation magnetization. Apart from the region of magnetic compensation the intrinsic FHR losses for 100 K c have been related directly to thermomagnetic properties of substituted YIG using nearly invariant matching parameters.

P. Roschmann

Papers

Anisotropy fields and FMR linewidth in single-crystal Al, Ga and Sc substituted hexagonal ferrites with M structure

Separation of anisotropy and porosity contributions to inhomogeneous broadened FMR linewidth in polycrystalline YIG

Annealing effects on cation distribution in diamagnetically substituted single crystal Yttrium Iron Garnet

Annealing effects on FMR linewidth in Ga substituted YIG

Intrinsic relaxation of the ferromagnetic resonance in substituted yttrium iron garnets