Spin transfer switching and spin polarization in magnetic tunnel junctions with MgO and AlOx barriers

Diao, Zhitao; Apalkov, Dmytro; Pakala, Mahendra; Ding, Yunfei; Panchula, Alex; Huai, Yiming

doi:10.1063/1.2139849

Cited by 209 publications

(107 citation statements)

References 23 publications

(12 reference statements)

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“…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.…”

mentioning

confidence: 99%

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: 99%

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

et al. 2007

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“…According to Fig. 2 of Diao et al [6] this implies a TMR decrease from ∼115% to ∼110%. The fractional decrease in TMR is less than 5% whereas the fractional increase in spin torque is ∼16%, estimated from the voltage increase between θ=0 and θ = π/4.…”

Section: Magnetic Tunnel Junctionsmentioning

confidence: 99%

“…6. We use device parameters corresponding to CoFeB MTJ's reported by Diao [6], but assume smaller RA products of the order of 1 Ωµm 2 [8]. Whereas trajectories such as those in Fig.…”

Section: Magnetic Tunnel Junctionsmentioning

confidence: 99%

“…However, the main challenges that must be overcome to implement spin transfer torque random access memory (STT-RAM) are (i) increasing the voltage swing to achieve integration into traditional GHz sensing circuitry, and (ii) reducing the critical current required to switch MTJ's to a level which makes them compatible with current CMOS technology [4]. MgO MTJ's fabricated with CoFeB low magnetization materials have shown tunneling magnetoresistance (TMR) exceeding 100% for devices with resistance in the kΩ range and switching currents ∼MA/cm 2 [5,6,7]. These devices not only exceed the required voltage swing threshold, but also reduce the critical switching current density J C to within the order of magnitude needed for CMOS integration.…”

Section: Introductionmentioning

confidence: 99%

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Effect of resistance feedback on spin torque-induced switching of nanomagnets

Garzon

Webb

Covington

et al. 2009

Journal of Magnetism and Magnetic Materials

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In large magnetoresistance devices spin torque-induced changes in resistance can produce GHz current and voltage oscillations which can affect magnetization reversal. In addition, capacitive shunting in large resistance devices can further reduce the current, adversely affecting spin torque switching. Here, we simultaneously solve the Landau-Lifshitz-Gilbert equation with spin torque and the transmission line telegrapher's equations to study the effects of resistance feedback and capacitance on magnetization reversal of both spin valves and magnetic tunnel junctions. While for spin valves parallel (P) to anti-parallel (AP) switching is adversely affected by the resistance feedback due to saturation of the spin torque, in low resistance magnetic tunnel junctions P-AP switching is enhanced. We study the effect of resistance feedback on the switching time of MTJ's, and show that magnetization switching is only affected by capacitive shunting in the pF range.

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“…Expanding the LM area requires a larger current to drive, since the STS is determined by current density. In order to obtain a better aperture ratio, we have to decrease switching current by increasing spin injection efficiency with highly spin polarized materials [18] or increasing the current supply capability of the backplane transistor. We are also considering the development of new techniques other than MTJ in which the switching current is independent of the element size.…”

Section: Magneto-optical Properties Of the Active Matrix Spin-slmmentioning

confidence: 99%

Two Micron Pixel Pitch Active Matrix Spatial Light Modulator Driven by Spin Transfer Switching

et al. 2016

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Abstract:We have developed an active matrix-addressed magneto-optical spatial light modulator driven by spin-transfer switching (spin-SLM) which has a 100 × 100 array pixel layout with a 2 µm pixel pitch. It has pixel-selection-transistors and logic circuits which convert serial data into parallel data to reduce input terminals. We have confirmed successful magnetization switching of each pixel by injecting a pulse current generated from the logic circuit, and its optical display capability by showing digital characters.

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Spin transfer switching and spin polarization in magnetic tunnel junctions with MgO and AlOx barriers

Cited by 209 publications

References 23 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

Effect of resistance feedback on spin torque-induced switching of nanomagnets

Two Micron Pixel Pitch Active Matrix Spatial Light Modulator Driven by Spin Transfer Switching

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