Current-Driven Magnetization Switching in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

Hayakawa, Jun; Ikeda, Shoji; Lee, Young Min; Sasaki, R.; Meguro, T.; Matsukura, F.; Takahashi, Hiromasa; Ohno, Hideo

doi:10.1143/jjap.44.l1267

Cited by 194 publications

(104 citation statements)

References 30 publications

(45 reference statements)

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“…For antiparallel alignment (curves A and B), the resistance decreases with increasing V b because new tunnelling channels open at higher bias voltages 15 . In contrast, for parallel alignments (C and D), resistances remain almost constant, as is commonly observed in MgO-based MTJs 16 . For curve B, angle θ 12 is defined as the angle between S 2 and S 1 , which is calculable from the resistance value by assuming a cosine dependence of tunnel conductance on θ 12 (ref.…”

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confidence: 76%

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Quantitative measurement of voltage dependence of spin-transfer torque in MgO-based magnetic tunnel junctions

et al. 2007

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When an electric current passes from one ferromagnetic layer via a non-magnetic layer into another ferromagnetic layer, the spin polarization and subsequent rotation of this current can induce a transfer of angular momentum that exerts a torque on the second ferromagnetic layer 1-4 . This provides a potentially useful method to reverse 3,5-7 and oscillate 8 the magnetic momenta in nanoscale magnetic structures. Owing to the large current densities required to observe spin-torqueinduced magnetization switching and microwave emission (∼10 7 A cm −2 ), accurately measuring the strength, or even the direction, of the associated spin torque has proved difficult. Yet, such measurements are crucial to refining our understanding of the mechanisms responsible and the theories that describe them 9,10 . To address this, we present quantitative experimental measurements of the spin torque in MgO-based magnetic tunnel junctions 11-14 for a wide range of bias currents covering the switching currents. The results verify the occurrence of two different spin-torque regimes with different bias dependences that agree well with theoretical predictions 10 .Magnetic tunnel junctions (MTJs) consisting of a MgO insulating layer sandwiched between two ferromagnetic layers (S 1 and S 2 in Fig. 1a) were used to provide very large magnetoresistance 11,14 . Such MTJs are now useful as data storage cells in magnetic random-access memories (M-RAMs) and as magnetic-field sensors in magnetic hard disk drives [11][12][13] . The MTJs with a layer structure of Ir-Mn/Co-Fe/Ru/Co 60 Fe 20 B 20 /MgO/Co 60 Fe 20 B 20 were prepared on a MgO substrate using an ultrahigh-vacuum sputtering system (C-7100; Canon ANELVA). The 3-nm-thick bottom Co-Fe-B layer (S 1 ) acts as a spin polarizer. The top Co-Fe-B layer (S 2 ), a 2-nm-thick free layer, is excited by the spin torque. The MgO tunnel barrier is about 1 nm thick. The MTJs are rectangular with dimensions of approximately 70 nm × 250 nm (see the Methods section for preparation details).Resistance-magnetic-field (R-H ) curves measured at a small bias voltage (0.1-0.3 mV) and different in-plane field directions, that is, θ H = 0 and 45 • , are shown in Fig. 1b. θ H is the angle between the applied field direction and the easy axis of the magnetic cell along the long axis of the rectangular cell (see Fig. 1a). The magnetoresistance ratio is defined as MR = (R AP − R P )/R P , where R P and R AP respectively represent resistance in the parallel and antiparallel magnetization alignments of S 1 and S 2 . A positive bias current denotes electron flow from S 2 to S 1 . The magnetoresistance ratio and R P at a small bias voltage are, respectively, 154% and about 120 (R P × (Junction area) = 2 µm 2 ). Figure 1c shows the bias voltage, V b , dependence of the tunnelling resistance, as measured in four different fields (A-D), which are indicated by arrows in Fig. 1b. For antiparallel alignment (curves A and B), the resistance decreases with increasing V b because new tunnelling channels open at higher bias voltages 1...

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confidence: 76%

“…Several groups have demonstrated switching in MgO-based MTJs 7,16,25 , thereby accelerating the development of M-RAMs with spin-torque writing 26,27 . In our experiment, switching was observed at around −270 mV for the antiparallel-to-parallel transition, where the STT is large, as shown in Fig.…”

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confidence: 99%

Quantitative measurement of voltage dependence of spin-transfer torque in MgO-based magnetic tunnel junctions

et al. 2007

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“…15͒ based MTJs, and facilitates record-low switching currents in spin-torque devices. 16 From our IETS spectra, we notice that for amorphous electrodes, the small grain size at the interface might induce a low energy cutoff in the magnon spectrum due to size quantization effects. On crystallization in the fcc ͑111͒ texture, the increase in grain size lifts the size quantization and, we observe the appearance of a distinct peak in the spectra which might be directly related to known magnon excitations in single crystalline fcc Co.…”

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confidence: 81%

Impact of interface crystallization on inelastic tunneling in Al∕AlOx∕CoFeB

Paluskar

Bloom

Swagten

et al. 2007

Applied Physics Letters

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We report the change in inelastic electron tunneling spectra (IETS) for Al∕AlOx∕CoFeB∕Al junctions when the structure of CoFeB at its interface with AlOx is intentionally changed from quasiamorphous to highly textured fcc. While for the quasiamorphous interface there are signs of the size quantization of magnons, the spectra for the fcc interface show distinct excitations at bias voltages associated with known surface magnon modes in fcc Co. These results demonstrate that IETS can be used as a tool to probe distinct structural changes of the magnetic electrode in tunnel junctions.

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“…Such large values result from the strong spin polarization induced by the crystalline structure of the ferromagnetic CoFeB electrodes together with the MgO barrier, translating into coherent tunneling through the barrier [74]. These large values are obtained only when both electrodes in contact with the MgO barrier show bcc crystalline structure with (1 0 0) out-of-plane texture, promoted in as-deposited amorphous-CoFeB upon annealing at 270-350 • C [75].…”

Section: Choice Of Electrode Materials For Tmr Sensorsmentioning

confidence: 99%

Linearization strategies for high sensitivity magnetoresistive sensors

Silva

Leitao

Valadeiro

et al. 2015

Eur. Phys. J. Appl. Phys.

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Abstract. Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of ∼40 pT/ √ Hz at 30 Hz, representing a step forward the low field detection at room temperature.

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Current-Driven Magnetization Switching in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

Cited by 194 publications

References 30 publications

Quantitative measurement of voltage dependence of spin-transfer torque in MgO-based magnetic tunnel junctions

Quantitative measurement of voltage dependence of spin-transfer torque in MgO-based magnetic tunnel junctions

Impact of interface crystallization on inelastic tunneling in Al∕AlOx∕CoFeB

Linearization strategies for high sensitivity magnetoresistive sensors

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