Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMagnetization dynamics and damping due to electron-phonon scattering in a ferrimagnetic exchange model
121
0
0.0
(
0
)
Added by
Hans Christian Schneider
Publication date
2014
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We present a microscopic calculation of magnetization damping for a magnetic toy model. The magnetic system consists of itinerant carriers coupled antiferromagnetically to a dispersionless band of localized spins, and the magnetization damping is due to coupling of the itinerant carriers to a phonon bath in the presence of spin-orbit coupling. Using a mean-field approximation for the kinetic exchange model and assuming the spin-orbit coupling to be of the Rashba form, we derive Boltzmann scattering integrals for the distributions and spin coherences in the case of an antiferromagnetic exchange splitting, including a careful analysis of the connection between lifetime broadening and the magnetic gap. For the Elliott-Yafet type itinerant spin dynamics we extract dephasing and magnetization times T_1 and T_2 from initial conditions corresponding to a tilt of the magnetization vector, and draw a comparison to phenomenological equations such as the Landau-Lifshitz or the Gilbert damping. We also analyze magnetization precession and damping for this system including an anisotropy field and find a carrier mediated dephasing of the localized spin via the mean-field coupling.
rate research
Read More
We study the heat-induced magnetization dynamics in a toy model of a ferrimagnetic alloy, which includes localized spins antiferromagnetically coupled to an itinerant carrier system with a Stoner gap. We determine the one-particle spin-density matrix including exchange scattering between localized and itinerant bands as well as scattering with phonons. While a transient ferromagnetic-like state can always be achieved by a sufficiently strong excitation, this transient ferromagnetic-like state only leads to magnetization switching for model parameters that also yield a compensation point in the equilibrium M(T) curve.
Recent investigations have advanced the understanding of how structure-property relationships in ferromagnetic metal alloys affect the magnetization dynamics on nanosecond time-scales. A similar understanding for magnetization dynamics on femto- to pico-second time-scales does not yet exist. To address this, we perform time-resolved magneto optic Kerr effect (TRMOKE) measurements of magnetization dynamics in Co-Fe alloys on femto- to nano-second regimes. We show that Co-Fe compositions that exhibit low Gilbert damping parameters also feature prolonged ultrafast demagnetization upon photoexcitation. We analyze our experimental TR-MOKE data with the three-temperature-model (3TM) and the Landau-Lifshitz-Gilbert equation. These analyses reveal a strong compositional dependence of the dynamics across all time-scales on the strength of electron-phonon interactions. Our findings are beneficial to the spintronics and magnonics community, and will aid in the quest for energy-efficient magnetic storage applications.
We determined the lattice dynamics of metastable, surface-stabilized $alpha$-phase FeSi$_2$ nanoislands epitaxially grown on the Si(111) surface with average heights and widths ranging from 1.5 to 20 nm and 18 to 72 nm, respectively. The crystallographic orientation, surface morphology and local crystal structure of the nanoislands were investigated by reflection high-energy electron diffraction, atomic force microscopy and X-ray absorption spectroscopy. The Fe-partial phonon density of states (PDOS), obtained by nuclear inelastic scattering, exhibits a pronounced damping and broadening of the spectral features with decreasing average island height. First-principles calculations of the polarization-projected Si- and Fe-partial phonon dispersions and PDOS enable the disentanglement of the contribution of the $xy$- and $z$-polarized phonons to the experimental PDOS. Modeling of the experimental data with the theoretical results unveils an enhanced damping of the $z$-polarized phonons for islands with average sizes below 10 nm. This phenomenon is attributed to the fact that the low-energy $z$-polarized phonons couple to the low-energy surface/interface vibrational modes. The thermodynamic and elastic properties obtained from the experimental data show a pronounced size-dependent behavior.
Landau level broadening mechanisms in electrically neutral and quasineutral graphene were investigated through micro-magneto-Raman experiments in three different samples, namely, a natural single-layer graphene flake and a back-gated single-layer device, both deposited over Si/SiO2 substrates, and a multilayer epitaxial graphene employed as a reference sample. Interband Landau level transition widths were estimated through a quantitative analysis of the magnetophonon resonances associated with optically active Landau level transitions crossing the energy of the E_2g Raman-active phonon. Contrary to multilayer graphene, the single-layer graphene samples show a strong damping of the low-field resonances, consistent with an additional broadening contribution of the Landau level energies arising from a random strain field. This extra contribution is properly quantified in terms of a pseudomagnetic field distribution Delta_B = 1.0-1.7 T in our single-layer samples.
We theoretically investigate pumping of phonons by the dynamics of a magnetic film into a non-magnetic contact. The enhanced damping due to the loss of energy and angular momentum shows interference patterns as a function of resonance frequency and magnetic film thickness that cannot be described by viscous (Gilbert) damping. The phonon pumping depends on magnetization direction as well as geometrical and material parameters and is observable, e.g., in thin films of yttrium iron garnet on a thick dielectric substrate.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
