2,498 research outputs found
Tunnel-barrier-enhanced dc voltage signals induced by magnetization dynamics in magnetic tunnel junctions
We theoretically study the recently observed tunnel-barrier-enhanced dc
voltage signals generated by magnetization precession in magnetic tunnel
junctions. While the spin pumping is suppressed by the high tunneling
impedance, two complimentary processes are predicted to result in a sizable
voltage generation in ferromagnet (F)|insulator (I)|normal-metal (N) and F|I|F
junctions, with one ferromagnet being resonantly excited. Magnetic dynamics in
F|I|F systems induces a robust charge pumping, translating into voltage in open
circuits. In addition, dynamics in a single ferromagnetic layer develops
longitudinal spin accumulation inside the ferromagnet. A tunnel barrier then
acts as a nonintrusive probe that converts the spin accumulation into a
measurable voltage. Neither of the proposed mechanisms suffers from spin
relaxation, which is typically fast on the scale of the exponentially slow
tunneling rates. The longitudinal spin-accumulation buildup, however, is very
sensitive to the phenomenological ingredients of the spin-relaxation picture.Comment: 5 pages, 2 figure
Spin and charge pumping in magnetic tunnel junctions with precessing magnetization: A nonequilibrium Green function approach
We study spin and charge currents pumped by precessing magnetization of a
single ferromagnetic layer within F|I|N or F|I|F (F-ferromagnet; I-insulator;
N-normal-metal) multilayers of nanoscale thickness attached to two normal metal
electrodes with no applied bias voltage between them. Both simple
one-dimensional model, consisting of a single precessing spin and a potential
barrier as the "sample," and realistic three-dimensional devices are
investigated. In the rotating reference frame, where the magnetization appears
to be static, these junctions are mapped onto a four-terminal dc circuit whose
effectively half-metallic ferromagnetic electrodes are biased by the frequency
of microwave radiation driving magnetization precession at the
ferromagnetic resonance (FMR) conditions. We show that pumped spin current in
F|I|F junctions, diminished behind the tunnel barrier and increased in the
opposite direction, is filtered into charge current by the second layer to
generate dc pumping voltage of the order of V (at FMR frequency
GHz) in an open circuit. In F|I|N devices, several orders of
magnitude smaller charge current and the corresponding dc voltage appear
concomitantly with the pumped spin current due to barrier induced asymmetry in
the transmission coefficients connecting the four electrodes in the rotating
frame picture of pumping.Comment: 8 pages, 5 figure
Parametric resonance of magnetization excited by electric field
Manipulation of magnetization by electric field is a central goal of
spintronics because it enables energy-efficient operation of spin-based
devices. Spin wave devices are promising candidates for low-power information
processing but a method for energy-efficient excitation of short-wavelength
spin waves has been lacking. Here we show that spin waves in nanoscale magnetic
tunnel junctions can be generated via parametric resonance induced by electric
field. Parametric excitation of magnetization is a versatile method of
short-wavelength spin wave generation, and thus our results pave the way
towards energy-efficient nanomagnonic devices
Magnetic Tunnel Junction-Based On-Chip Microwave Phase and Spectrum Analyzer
A magnetic tunnel junction (MTJ)-based microwave detector is proposed and investigated. When the MTJ is excited by microwave magnetic fields, the relative angle between the free layer and pinned layer alternates, giving rise to an average resistance change. By measuring the average resistance change, the MTJ can be utilized as a microwave power sensor. Due to the nature of ferromagnetic resonance, the frequency of an incident microwave is directly determined. In addition, by integrating a mixer circuit, the MTJ-based microwave detector can also determine the relative phase between two microwave signals. Thus, the MTJbased microwave detector can be used as an on-chip microwave phase and spectrum analyzer
Tunnel barrier enhanced voltage signals generated by magnetization precession of a single ferromagnetic layer
We report the electrical detection of magnetization dynamics in an
Al/AlOx/Ni80Fe20/Cu tunnel junction, where a Ni80Fe20 ferromagnetic layer is
brought into precession under the ferromagnetic resonance (FMR) conditions. The
dc voltage generated across the junction by the precessing ferromagnet is
enhanced about an order of magnitude compared to the voltage signal observed
when the contacts in this type of multilayered structure are ohmic. We discuss
the relation of this phenomenon to magnetic spin pumping and speculate on other
possible underlying mechanisms responsible for the enhanced electrical signal
- …