Low relaxation rate in a low-Z alloy of iron

The longest relaxation time and sharpest frequency content in ferromagnetic precession is determined by the intrinsic (Gilbert) relaxation rate \emph{$G$}. For many years, pure iron (Fe) has had the lowest known value of $G=\textrm{57 Mhz}$ for all pure ferromagnetic metals or binary alloys. We show that an epitaxial iron alloy with vanadium (V) possesses values of $G$ which are significantly reduced, to 35$\pm$5 Mhz at 27% V. The result can be understood as the role of spin-orbit coupling in generating relaxation, reduced through the atomic number $Z$.Comment: 14 pages, 4 figure

Theory of Current-Induced Magnetization Precession

We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to demonstrate that unpolarized current flow from a non-magnet into a ferromagnet can produce a precession-type instability of the magnetization. The fundamental origin of the instability is the difference in conductivity between majority spins and minority spins in the ferromagnet. This leads to spin accumulation and spin currents that carry angular momentum across the interface. The component of this angular momentum perpendicular to the magnetization drives precessional motion that is opposed by Gilbert damping. Neglecting magnetic anisotropy and magnetostatics, our approximate analytic and exact numerical solutions using realistic values for the material parameters show (for both semi-infinite and thin film geometries) that a linear instability occurs when both the current density and the excitation wave vector parallel to the interface are neither too small nor too large. For many aspects of the problem, the variation of the magnetization in the direction of the current flows makes an important contribution.Comment: Submitted to Physical Review

Semiconductor Spintronics

Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent nteraction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.Comment: tutorial review; 342 pages, 132 figure

THE g-FACTOR AND SURFACE MAGNETIZATION OF PURE IRON ALONG [100] AND [111] DIRECTIONS

En vue de la détermination exacte du facteur g du fer nous avons étudié la résonance ferromagnétique entre 12 et 70 GHz sur des monocristaux en forme de whiskers dans les directions [100] et [111], à la température ambiante. Le facteur g est le même pour les deux directions (2,089 ± 0,007), et indépendant de la fréquence. La valeur de l'intensité de l'aimantation est déduite des mesures de l'antirésonance à 70 GHz, les résultats montrent une petite anisotropie (M100 = 1 697,3 u. e. m./cm3 ; M111 = 1 700,0 u. e.m./cm3).In order to obtain exact values of the spectroscopic splitting factor in pure iron along the [100] and [111] crystallographic directions, measurements of ferromagnetic resonance in whisker type single crystals have been performed in the frequency range 12 + 70 GHz, at room temperature. The results show that the g-factor is independent on frequency in the given range and yield the value g = 2.089 ± 0.007 for both directions. A slight anisotropy of the surface magnetization has been found (M100 = 1 697.3 e. m. u./cm3 ; M111 = 1700.0 e. m. u./cm3) using the antiresonance measurement at 70 GHz

FMR and Static Magnetic Properties of Gallium Substituted Magnetoplumbite

Magnetization and uniaxial anisotropy were studied on single crystals of PbFe12-xGaxO19, where x = 0 - 8 from 2 to 360 K. The results suggest that for x > 3 the spin arrangement becomes non-collinear. The magnetic moment and anisotropy for x < 3 are roughly consistent with the random distribution of Ga3+ ions in all sites except for 2b. For x = 5.94 and 8.02 the relatively large anisotropy of the Curie temperature was found. The FMR measurements at T = 300 K were interpred using the g-tensor formulation