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▲ [16a-C41-4] Investigation of the spin-transfer torque generated by anomalous Hall effect
Keywords:Anomalous Hall effect, Spin-transfer torque, Ferromagnetic resonance
Spin-Hall effect (SHE) has attracted much attention for three-terminal spintronics devices. Liu et al. demonstrated that magnetization can be switched by the spin Hall torque [1]. In the case of a perpendicularly magnetized ferromagnet, however, it is difficult to induce the magnetization switching by SHE, because the spin Hall torque becomes zero when the magnetization crosses the film plane, resulting in the probabilistic switching. To make the switching deterministic, an external magnetic field [2] or exchange bias field along the current direction [3] is required. Recently, it was theoretically predicted that anomalous Hall effect (AHE) can switch deterministically the magnetization of the perpendicularly magnetized ferromagnet without a magnetic field [4]. In this study, we experimentally investigate the AHE-induced spin-transfer torque by measuring the spin-torque diode effect in magnetic tunnel junction in addition to CoFeB-based AHE structure.
We prepared films with a stacking structure of sub. / seed layer / PtMn / CoFeB / Ru / CoFeB (pinned layer)/ Cu / CoFeB (free layer)/ MgO / CoFeB (reference layer) / W / CoFe / Ru / CoFe / IrMn. The film was patterned into a magnetic tunnel junction (MTJ) of 1 mm in diameter. An in-plane current (Iin-plane) was injected through the bottom lead, and an in-plane magnetic field of 100 mT was applied in an angle (ΦH) respect to the magnetization direction of the CoFeB reference layer. The spectra were fitted by the summation of asymmetric and symmetric Lorentzian as shown by blue curves. From the fitting, resonance frequency (f0) and linewidth (δf) of the spectrum were evaluated. Linear decrease of f0 was observed with increasing Iin-plane, which is explained by Oersted field generated by Iin-plane. We had expected the enhancement or reduction of the linewidth due to the spin-transfer torque by AHE, as in the case of the spin torque diode effect in an MTJ [5]. Experimentally, however, the effect of Iin-plane on δf has not been observed clearly yet. We will discuss the effect of magnetic field angle (ΦH) on the spectrum based on a theoretical model considering AHE-induced spin torque.
[1] L. Liu et al., Science 336, 555 (2012).
[2] M. Cubukcu et al., Appl. Phys. Lett. 104, 042406 (2014). I. M. Miron et al., Nature 476, 189 (2011).
[3] S. Fukami et al., Nat. Mater. 15, 535 (2016).
[4] T. Taniguchi et al. Phys. Rev. Appl. 3, 044001 (2015). [5] H. Kubota et al., Nat. Phys. 4, 37 (2008).
We prepared films with a stacking structure of sub. / seed layer / PtMn / CoFeB / Ru / CoFeB (pinned layer)/ Cu / CoFeB (free layer)/ MgO / CoFeB (reference layer) / W / CoFe / Ru / CoFe / IrMn. The film was patterned into a magnetic tunnel junction (MTJ) of 1 mm in diameter. An in-plane current (Iin-plane) was injected through the bottom lead, and an in-plane magnetic field of 100 mT was applied in an angle (ΦH) respect to the magnetization direction of the CoFeB reference layer. The spectra were fitted by the summation of asymmetric and symmetric Lorentzian as shown by blue curves. From the fitting, resonance frequency (f0) and linewidth (δf) of the spectrum were evaluated. Linear decrease of f0 was observed with increasing Iin-plane, which is explained by Oersted field generated by Iin-plane. We had expected the enhancement or reduction of the linewidth due to the spin-transfer torque by AHE, as in the case of the spin torque diode effect in an MTJ [5]. Experimentally, however, the effect of Iin-plane on δf has not been observed clearly yet. We will discuss the effect of magnetic field angle (ΦH) on the spectrum based on a theoretical model considering AHE-induced spin torque.
[1] L. Liu et al., Science 336, 555 (2012).
[2] M. Cubukcu et al., Appl. Phys. Lett. 104, 042406 (2014). I. M. Miron et al., Nature 476, 189 (2011).
[3] S. Fukami et al., Nat. Mater. 15, 535 (2016).
[4] T. Taniguchi et al. Phys. Rev. Appl. 3, 044001 (2015). [5] H. Kubota et al., Nat. Phys. 4, 37 (2008).