6 research outputs found
Observation of spin-transfer switching in deep submicron-sized and low-resistance magnetic tunnel junctions
The spin-transfer effect has been studied in magnetic tunnel junctions
(PtMn/CoFe/Ru/CoFe/Al2O3/CoFe/NiFe) with dimensions down to 0.1x0.2 um2 and
resistance-area product RA in the range of 0.5-10 Ohm m2 (dR/R=1-20%).
Current-induced magnetization switching is observed with a critical current
density of about 8e6 A/cm2. The attribution of the switching to the
spin-transfer effect is supported by a current-induced dR/R value identical to
the one obtained from the R versus H measurements. Furthermore, the critical
switching current density has clear dependence on the applied magnetic field,
consistent with what has been observed previously in the case of spin-transfer
induced switching in metallic multilayer systems
Critical Current Distribution in Spin Transfer Switched Magnetic Tunnel Junctions
The spin transfer switching current distribution within a cell was studied in
magnetic tunnel junction based structures having alumina barriers with
resistance-area product (RA) of 10 to 30 Ohm-um2 and tunneling
magneto-resistance (TMR) of ~20%. These were patterned into current
perpendicular to plane configured nano-pillars having elliptical cross-sections
of area ~0.02 um2. The width of the critical current distribution
(sigma/average of distribution), measured using 30 ms current pulse width, was
found to be 7.5% and 3.5% for cells with thermal factor (KuV/kBT) of 40 and 65
respectively. The distribution width did not change significantly for pulse
widths between 1 s and 4 ms. An analytical expression for probability density
function, p(I/Ico) was derived considering the thermally activated spin
transfer model, which supports the experimental observation that the thermal
factor is the most significant parameter in determining the within cell
critical current distribution width.Comment: 12 pages, 4 figure
Spin Transfer Switching and Spin Polarization in Magnetic Tunnel Junctions with Mgo and Alox Barriers
We present spin transfer switching results for MgO based magnetic tunneling
junctions (MTJs)with large tunneling magnetoresistance (TMR) ratio of up to
150% and low intrinsic switching current density of 2-3 x 10 MA/cm2. The
switching data are compared to those obtained on similar MTJ nanostructures
with AlOx barrier. It is observed that the switching current density for MgO
based MTJs is 3-4 times smaller than that for AlOx based MTJs, and that can be
attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In
addition, we report a qualitative study of TSP for a set of samples, ranging
from 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at
finite bias) responsible for the current-driven magnetization switching is
suppressed as compared to zero-bias tunneling spin polarization determined from
TMR.Comment: To appear in Appl. Phys. Lett. soo
Spin-Polarized Current Induced Torque in Magnetic Tunnel Junctions
We present tight-binding calculations of the spin torque in non-collinear
magnetic tunnel junctions based on the non-equilibrium Green functions
approach. We have calculated the spin torque via the effective local magnetic
moment approach and the divergence of the spin current. We show that both
methods are equivalent, i.e. the absorption of the spin current at the
interface is equivalent to the exchange interaction between the electron spins
and the local magnetization. The transverse components of the spin torque
parallel and perpendicular to the interface oscillate with different phase and
decay in the ferromagnetic layer (FM) as a function of the distance from the
interface. The period of oscillations is inversely proportional to the
difference between the Fermi-momentum of the majority and minority electrons.
The phase difference between the two transverse components of the spin torque
is due to the precession of the electron spins around the exchange field in the
FM layer. In absence of applied bias and for a relatively thin barrier the
perpendicular component of the spin torque to the interface is non-zero due to
the exchange coupling between the FM layers across the barrier.Comment: 6 pages, 3 figure