2,592 research outputs found
Zero Field precession and hysteretic threshold currents in spin torque oscillators with tilted polarizer
Using non-linear system theory and numerical simulations we map out the
static and dynamic phase diagram in zero applied field of a spin torque
oscillator with a tilted polarizer (TP-STO).We find that for sufficiently large
currents, even very small tilt angles (beta>1 degree) will lead to steady free
layer precession in zero field. Within a rather large range of tilt angles, 1
degree< beta <19 degree, we find coexisting static states and hysteretic
switching between these using only current. In a more narrow window (1
degree<beta<5 degree) one of the static states turns into a limit cycle
(precession). The coexistence of static and dynamic states in zero magnetic
field is unique to the tilted polarizer and leads to large hysteresis in the
upper and lower threshold currents for TP-STO operation.Comment: 5 pages, 4 figure
Trends in Elasticity and Electronic Structure of Transition-Metal Nitrides and Carbides from First Principles
The elastic properties of the -structured transition-metal nitrides and
their carbide counterparts are studied using the {\it ab initio\} density
functional perturbation theory. The linear response results of elastic
constants are in excellent agreement with those obtained from numerical
derivative methods, and are also consistent with measured data. We find the
following trends: (1) Bulk moduli and tetragonal shear moduli
, increase and lattice constants decrease
rightward or downward on the Periodic Table for the metal component or if C is
replaced by N; (2) The inequality holds for
; (3) depends strongly on the number of valence electrons per
unit cell (). From the fitted curve of as a function of , we
can predict that MoN is unstable in structure, and transition-metal
carbonitrides ( ZrCN) and di-transition-metal carbides
( HfTaC) have maximum at .Comment: 4 pages, 2 figures, submitted to PRL. 2 typos in ref. 15 were
correcte
The NMR of High Temperature Superconductors without Anti-Ferromagnetic Spin Fluctuations
A microscopic theory for the NMR anomalies of the planar Cu and O sites in
superconducting La_1.85Sr_0.15CuO_4 is presented that quantitatively explains
the observations without the need to invoke anit-ferromagnetic spin
fluctuations on the planar Cu sites and its significant discrepancy with the
observed incommensurate neutron spin fluctuations. The theory is derived from
the recently published ab-initio band structure calculations that correct LDA
computations tendency to overestimate the self-coulomb repulsion for the
half-filled Cu d_x2-y2 orbital for these ionic systems. The new band structure
leads to two bands at the Fermi level with holes in the Cu d_z2 and apical O
p_z orbitals in addition to the standard Cu d_x2-y2 and planar O p_sigma
orbitals. This band structure is part of a new theory for the cuprates that
explains a broad range of experiments and is based upon the formation of Cooper
pairs comprised of a k up spin electron from one band and a -k down spin
electron from another band (Interband Pairing Model).Comment: In Press, Journal of Physical Chemistry. See also
http://www.firstprinciples.com. Minor changes to references and figure
readabilit
Moderate Surface Segregation Promotes Selective Ethanol Production in CO Hydrogenation Reaction over CoCu Catalysts
Model of C-Axis Resistivity of High-\Tc Cuprates
We propose a simple model which accounts for the major features and
systematics of experiments on the -axis resistivity, , for \lsco,
\ybco and \bsco . We argue that the -axis resistivity can be separated
into contributions from in-plane dephasing and the -axis ``barrier''
scattering processes, with the low temperature semiconductor-like behavior of
arising from the suppression of the in-plane density of states
measured by in-plane magnetic Knight shift experiments. We report on
predictions for in impurity-doped \ybco materials.Comment: 10 pages + figures, also see March Meeting J13.1
Pseudo Spin Valves Using a (112)-textured DO_22 MnGa Fixed Layer
We demonstrate pseudo spin valves with a (112)-textured DO_22 MnGa (MnGa)
tilted magnetization fixed layer and an in-plane CoFe free layer. Single D0_22
MnGa films exhibit a small magnetoresistance (MR) typically observed in metals.
In MnGa/Cu/ CoFe spin valves a transition from a negative (-0.08%) to positive
(3.88%) MR is realized by introducing a thin spin polarizing CoFe insertion
layer at the MnGa/Cu interface and tailoring the MnGa thickness. Finally, the
exchange coupling between the MnGa and CoFe insertion layer is studied using a
first-order reversal curve (FORC) technique.Comment: 5 pages, 4 figures, submitted to IEEE Magnetics Letter
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