Angle dependence of the ferromagnetic resonance linewidth in easy-axis and easy-plane single crystal hexagonal ferrite disks

Abstract

Ferromagnetic resonance measurements were made as a function of the static external field angle for c-plane disks of single crystal flux grown manganese substituted barium M-type ͑Ba-M ͒ and zinc Y-type ͑Zn-Y ͒ hexagonal ferrites at 50 and 8.8 GHz, respectively. A shorted waveguide technique was used. Analysis of the FMR field versus angle results confirmed the operational assumption of a uniform mode response. For the easy-axis Ba-M disk, the linewidth was 69 Oe when the external field and magnetization vectors were perpendicular to the disk. The linewidth increased to a maximum measured value of 472 Oe when the magnetization was directed 45.4°from the sample normal. For the easy-plane Zn-Y disk, the linewidth had a minimum value of 18 Oe when the field and magnetization vectors were in-plane. The maximum linewidth was 391 Oe when the magnetization was directed 25.2°from the disk normal. The linewidths were larger than predicted for reasonable values of the Landau-Lifshitz damping and showed angle dependences which indicated nonintrinsic contributions to the loss. A modified two magnon scattering calculation based on the model of Sparks, Loudon, and Kittel was used to investigate these linewidth differences. The calculation included anisotropy modifications to the spin wave band for each material. The angle dependences of the excess linewidths show qualitative agreement with the two magnon predictions, with inhomogeneity sizes on the order of 1 and 0.25 m and volume fractions of 0.01 and 0.005 for the Ba-M and Zn-Y disks, respectively.

Nanosecond magnetic relaxation processes in ultrathin metallic films prepared by MBE

“…3 The two magnon scattering process has been used extensively to describe extrinsic damping in ferrites. [3][4][5][6][7] The Patton group pioneered the use of two magnon scattering in metallic films. 8 In a wide range of metallic amorphous ribbons, 9 films, 10 and metallic ultrathin film multilayers 1,11,12 the ferromagnetic resonance ͑FMR͒ linewidth, ⌬H, above 10 GHz is not only proportional to the microwave angular frequency, , as expected from the Gilbert damping but possesses a zerofrequency offset ⌬H(0),…”

FMR studies of exchange-coupled multiferroic polycrystalline Pt/BiFeO3/Ni81Fe19/Pt heterostructures

“…The intrinsic damping parameter ⊥ α in out-of-plane perpendicular geometry is usually lower than that of the in-plane parallel geometry [52], for t BFO = 39 nm ⊥ α = 0.018 ( α = 0.049). The damping dependence on the applied static magnetic field direction leads the damping parameter difference in both geometries to be related to the two-magnon scattering processes.…”

“…It is well known that, for perpendicular geometry, the FMR frequency lies near the bottom of the spin-wave manifold and there are few degenerate states. In the out-of-plane parallel geometry, the spin-wave manifold shifts down in frequency in such a way that the FMR frequency is at the top of the band and there are more degenerate states available [52].…”

Spin dynamics in ultrathin film structures with a network of misfit dislocations

“…Two magnon scattering has been used to describe extrinsic damping in ferrites 11,12 and metallic films. 13 The two magnon scattering matrix is proportional to components of the Fourier transform A(q)ϭ͐dr⌬U(r)e Ϫiqr of magnetic inhomogeneities, where U(r) stands symbolically for a local magnetic energy.…”