10
P. K. Muduli et al.
0
100 200 300 400 500
-0.006
0.000
0.006
0.012
0.018
Voltage (mV)
MR = 73%
MR = 67%
MR = 60%
0
100 200 300 400 500
-0.020
-0.016
-0.012
-0.008
-0.004
0.000
Voltage (mV)
MR = 73%
MR = 67%
MR = 60%
(a)
(b)
Fig. 5 Bias dependence of the (a) IP torkance, and (b) OOP torkance determined from the room
temperature FM-STFMR signals, for the three devices having different MR ratios. Reprinted from
Tiwari et al. [59], with the permission of AIP Publishing
certain range of bias voltages) even for nominally symmetric MTJs, and that any
quadratic term is negligible.
In a recent work by Tiwari et al. [59], bias dependence of spin torques in MgObased magnetic tunnel junction using a field-modulated spin torque ferromagnetic
resonance measurement technique is studied for three devices with tunneling magnetoresistance (MR) of 60, 67, and 73%. The devices with lower MR ratio showed the
presence of multiple modes, which can be ascribed to asymmetric modes originating
from inhomogeneous magnetization precession in the FL due to non-uniform currents (arising, e.g., from pinholes), while the device with higher MR device (73%),
showed a single resonance mode. It is found that the quality of the barrier certainly
has an effect on the in-plane torkance, and larger MR means larger efficiency in
spin-symmetric injection, which should lead to larger in-plane spin transfer torque.
The bias dependence of in-plane (IP) and out-of-plane (OOP) torkance are shown
in Figs. 5a, b, respectively. Figure 5a shows that IP torkance depends strongly on
the bias voltage. The magnitude of STT is higher for higher MR device. However,
the OOP torkance is almost constant for all the devices, which implies a linear
dependence of OOP torque on the bias voltage, which is consistent with studies
performed in Ref. [40, 50, 52, 55] but inconsistent with other works [32, 57]. Also,
the magnitude of OOP torkance is two orders of magnitude below the magnitude of
IP torkance, in contrast from previous works [48, 60]. The OOP torkance also shows
a change of its sign at higher bias. They also observe this behavior in other low MR
devices (<65%) and it is because of the sign change of the antisymmetric amplitude
(V a ) at higher bias. The origin of this behavior was attributed to second–order term in
the field-like torque which appears as a linear term in torkance. These results suggest
that bias dependence of torques depends on the MR ratio and this could be the reason
for reported different behaviors of torques as functions of bias voltage, especially
the field-like torque.
P. K. Muduli et al.
0
100 200 300 400 500
-0.006
0.000
0.006
0.012
0.018
Voltage (mV)
MR = 73%
MR = 67%
MR = 60%
0
100 200 300 400 500
-0.020
-0.016
-0.012
-0.008
-0.004
0.000
Voltage (mV)
MR = 73%
MR = 67%
MR = 60%
(a)
(b)
Fig. 5 Bias dependence of the (a) IP torkance, and (b) OOP torkance determined from the room
temperature FM-STFMR signals, for the three devices having different MR ratios. Reprinted from
Tiwari et al. [59], with the permission of AIP Publishing
certain range of bias voltages) even for nominally symmetric MTJs, and that any
quadratic term is negligible.
In a recent work by Tiwari et al. [59], bias dependence of spin torques in MgObased magnetic tunnel junction using a field-modulated spin torque ferromagnetic
resonance measurement technique is studied for three devices with tunneling magnetoresistance (MR) of 60, 67, and 73%. The devices with lower MR ratio showed the
presence of multiple modes, which can be ascribed to asymmetric modes originating
from inhomogeneous magnetization precession in the FL due to non-uniform currents (arising, e.g., from pinholes), while the device with higher MR device (73%),
showed a single resonance mode. It is found that the quality of the barrier certainly
has an effect on the in-plane torkance, and larger MR means larger efficiency in
spin-symmetric injection, which should lead to larger in-plane spin transfer torque.
The bias dependence of in-plane (IP) and out-of-plane (OOP) torkance are shown
in Figs. 5a, b, respectively. Figure 5a shows that IP torkance depends strongly on
the bias voltage. The magnitude of STT is higher for higher MR device. However,
the OOP torkance is almost constant for all the devices, which implies a linear
dependence of OOP torque on the bias voltage, which is consistent with studies
performed in Ref. [40, 50, 52, 55] but inconsistent with other works [32, 57]. Also,
the magnitude of OOP torkance is two orders of magnitude below the magnitude of
IP torkance, in contrast from previous works [48, 60]. The OOP torkance also shows
a change of its sign at higher bias. They also observe this behavior in other low MR
devices (<65%) and it is because of the sign change of the antisymmetric amplitude
(V a ) at higher bias. The origin of this behavior was attributed to second–order term in
the field-like torque which appears as a linear term in torkance. These results suggest
that bias dependence of torques depends on the MR ratio and this could be the reason
for reported different behaviors of torques as functions of bias voltage, especially
the field-like torque.