34
P. K. Muduli et al.
multiple RF signals was also shown using these detectors [145]. The advantage of
this technique is that the generated voltage signal is independent of the input RF
power. However, the technique does not work for low RF power, and a threshold
RF power is needed for the detection. The frequency of operation (<500 MHz) of
the detector is also significantly lower than that of standard in-plane magnetized
MTJ-based detectors.
9.1.4 Enhancement of Sensitivity Using Voltage Controlled Magnetic
Anisotropy
MTJs with large perpendicular magnetic anisotropy (PMA) often show a change in
the anisotropy value when a bias (or electric field) is applied across the device [146,
147]. This electric field induces certain interfacial magnetoelectric effects that affect
the availability of electronic states for different spin orientations [148]. The resulting
imbalance leads to a change in out-of-plane anisotropy. This effect, called voltagecontrolled magnetic anisotropy (VCMA), has been shown to have uses in several
applications, such as magnetization switching [12, 149–152] and phase noise reduction [153]. VCMA is also shown to excite voltage induced FMR dynamics at radio
frequencies (GHz) [34, 36, 154–156].
In 2012, Nozaki et al. [154] reported the possibility to excite ferromagnetic resonance by using VCMA in FeCo monolayers. Zhu et al. [34] later reported that the
inclusion of VCMA in exciting FMR dynamics leads to an extra antisymmetric term
in the STFMR spectra, which increases the RF sensitivity. Figure 21a shows the
calculated STFMR spectra of an MTJ including only VCMA for two different field
directions. The calculation is done using macrospin simulations by neglecting the
Fig. 21 a Calculated STFMR spectra generated by resistance oscillations due to the effect of
VCMA. The opposite signs of the antisymmetric component at the 0 ◦ (H x > 0) and 180 ◦ (H x < 0)
field directions (w.r.t. the fixed layer polarization) are a signature of VCMA. b Experimental result
showing an increase in sensitivity of ∼ 39% with the inclusion of VCMA effect. Reprinted from
Zhu et al. [34] Copyright (2012) by the American Physical Society
P. K. Muduli et al.
multiple RF signals was also shown using these detectors [145]. The advantage of
this technique is that the generated voltage signal is independent of the input RF
power. However, the technique does not work for low RF power, and a threshold
RF power is needed for the detection. The frequency of operation (<500 MHz) of
the detector is also significantly lower than that of standard in-plane magnetized
MTJ-based detectors.
9.1.4 Enhancement of Sensitivity Using Voltage Controlled Magnetic
Anisotropy
MTJs with large perpendicular magnetic anisotropy (PMA) often show a change in
the anisotropy value when a bias (or electric field) is applied across the device [146,
147]. This electric field induces certain interfacial magnetoelectric effects that affect
the availability of electronic states for different spin orientations [148]. The resulting
imbalance leads to a change in out-of-plane anisotropy. This effect, called voltagecontrolled magnetic anisotropy (VCMA), has been shown to have uses in several
applications, such as magnetization switching [12, 149–152] and phase noise reduction [153]. VCMA is also shown to excite voltage induced FMR dynamics at radio
frequencies (GHz) [34, 36, 154–156].
In 2012, Nozaki et al. [154] reported the possibility to excite ferromagnetic resonance by using VCMA in FeCo monolayers. Zhu et al. [34] later reported that the
inclusion of VCMA in exciting FMR dynamics leads to an extra antisymmetric term
in the STFMR spectra, which increases the RF sensitivity. Figure 21a shows the
calculated STFMR spectra of an MTJ including only VCMA for two different field
directions. The calculation is done using macrospin simulations by neglecting the
Fig. 21 a Calculated STFMR spectra generated by resistance oscillations due to the effect of
VCMA. The opposite signs of the antisymmetric component at the 0 ◦ (H x > 0) and 180 ◦ (H x < 0)
field directions (w.r.t. the fixed layer polarization) are a signature of VCMA. b Experimental result
showing an increase in sensitivity of ∼ 39% with the inclusion of VCMA effect. Reprinted from
Zhu et al. [34] Copyright (2012) by the American Physical Society