Influence of MgO tunnel barrier thickness on spin-transfer ferromagnetic resonance and torque in magnetic tunnel junctions

Skowroński, Witold; Czapkiewicz, M.; Frankowski, Marek; Wrona, Jerzy; Stobiecki, T.; Reiss, Günter; Chalapat, Khattiya; Paraoanu, G. S.; Dijken, Sebastiaan van

doi:10.1103/physrevb.87.094419

Cited by 20 publications

(19 citation statements)

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“…Thus, setting the power of the RF generator to 100 µW (-10 dBm), only 1% (1-Γ 2 ) , i.e., 1 µW is applied to the MTJ, which results in I RF = 7.3 µA RF current and J RF = 5.9×10 7 A/m 2 current density. We note that such current densities are sufficient to excite the magnetization dynamics by means of STT effect [14,15]. Figure 2 presents resistance vs. in-plane and perpendicular magnetic field curves, measured for different bias voltage polarity.…”

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confidence: 93%

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Spin-torque diode radio-frequency detector with voltage tuned resonance

Skowroński

Frankowski

Wrona

et al. 2014

Applied Physics Letters

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We report on a voltage tunable radio-frequency (RF) detector based on a magnetic tunnel junction (MTJ). The spin-torque diode effect is used to excite and/or detect RF oscillations in the magnetic free layer of the MTJ. In order to reduce the overall in-plane magnetic anisotropy of the free layer, we take advantage of the perpendicular magnetic anisotropy at the interface between ferromagnetic and insulating layers. The applied bias voltage is shown to have a significant influence on the magnetic anisotropy, and thus on the resonance frequency of the device. This influence also depends on the voltage polarity. The obtained results are accounted for in terms of the interplay of spin-transfertorque and voltage-controlled magnetic anisotropy effects.Due to spin wave excitations, magnetic thin films can emit and/or absorb electromagnetic signals in a microwave frequency range determined by ferromagnetic resonance (FMR). In turn, radio-frequency (RF) signals can be produced in magnetic tunnel junctions (MTJs) via the spin-transfer-torque (STT) effect [1,2], where a spin polarized current excites magnetization precession with a frequency that depends, among others, on the magnetic anisotropy. This precession gives rise to an electric signal that can be used in various devices, like spin wave generators [3] or spin-torque oscillators [4,5]. The inverse effect, i.e., absorption of RF spin currents by a MTJ produces a detectable DC signal [6]. This phenomenon, called the spin-torque diode effect, can be used as an RF-detector of very high sensitivity [7]. Recently, it has been shown that similar behavior can be achieved with alternatingvoltage-controlled magnetic anisotropy (VCMA) [8,9]. In this paper we propose a voltage tunable spin-torque diode, that is capable of sensing RF signals of different frequencies. We achieved such a functionality by using a combination of the STT and VCMA effects. The former effect produces the DC voltage in response to AC current, while the latter one changes the resonance detection regime. In addition, using a specially designed MTJ, we are able to measure STT components in a volt- * Electronic address: skowron@agh.edu.pl age range of ±1 V, which to our knowledge is beyond the STT measurements published to date (up to ±0.5 V in Ref. [10]) and reveals a non-linear behavior of the in-plane STT component vs. bias voltage [11,12]. To achieve the above objective, we have investigated MTJs with the following multilayer structure: SiO 2 (substrate) / 5 Ta / 30 CuN / 3 Ta / 30 CuN / 3 Ta / 16 Pt 38 Mn 62 / 2.1 Co 70 Fe 30 / 0.9 Ru / 2.3 Co 40 Fe 40 B 20 / 1.6 MgO / 1-2 Co 40 Fe 40 B 20 / 10 Ta / 7 Ru (thickness in nm). By varying thickness of the CoFeB free layer (FL), we observed a transition from in-plane to perpendicular anisotropy at a critical thickness of t c ≈ 1.35 nm [13]. After deposition, the MTJs were annealed at 250 • C in an in-plane magnetic field of 0.4 T in order to set the exchange bias direction and to improve the crystallization of the ferromagnetic electrodes. For the transpor...

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confidence: 93%

“…The FMR spectra were simulated using similar approach as in Ref. [15]. Examples of OOMMF results obtained for perpendicular field of H = 0 and 1000 Oe are depicted in Fig.…”

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confidence: 99%

Spin-torque diode radio-frequency detector with voltage tuned resonance

Skowroński

Frankowski

Wrona

et al. 2014

Applied Physics Letters

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“…Space discretization cell size has been set to 2 × 2 × 1 nm which resulted in 75 000 cells. Details of the investigated system has been described in [8]. The micromagnetic model of MTJ, current density distributions and approach for current-magnetization interaction via STT and tunnel magnetoresistance [24] have been described in [17].…”

Section: Examplementioning

confidence: 99%

“…We depict simple command line interface, allowing for fast and easy running of SSA. We present an example based on our previous investigations of inhomogeneous STT-induced microwave oscillations in MTJ [8,17]. Finally, efficiency and scalability tests are disused.…”

Section: Introductionmentioning

confidence: 95%

“…The dynamic behavior of the magnetization in continuous and nano-patterned mono-and multi-layer systems is widely investigated. Among the most important structures let us mention: Magnetic Tunnel Junctions (MTJs) with applications to memory [4,5], microwave generation [6][7][8] and sensing devices [9,10]; nano-wires [11] or magnonic crystals [12].…”

Section: Introductionmentioning

confidence: 99%

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