Spin-transfer in nanopillars with a perpendicularly magnetized spin polarizer

Abstract

Spin-transfer devices that incorporate a polarizer with its magnetization orthogonal to a switchable (free) layer offer the potential for ultra-fast switching, low power consumption and reliable operation. The non-collinear magnetizations lead to large initial spin-transfer torques, eliminating the incubation delay seen in devices with collinear magnetization. Here we present the basic electrical and magnetic characteristics of spin-valve nanopillars that incorporate a perpendicularly magnetized polarizer and demonstrate current-induced switching with short current pulses, down to 100 ps in duration. We have fabricated devices that have a CoNi polarizer with perpendicular magnetization and an in-plane magnetized 3 nm thick Co free layer and a 12 nm thick Co reference layer, each separated by thin (∼ 10 nm) Cu layers. The magnetization of the reference layer is collinear with that of free layer to read out the device state. The reference layer also contributes to the spin-accumulation acting on the free layer and leads to a spin-torque that favors the parallel (P) or antiparallel (AP) state depending on the current pulse polarity, reducing the requirement of precise pulse timing in precessional reversal. The anisotropy field of the perpendicular polarizer is 1.3 T, i.e. it is high enough so that in-plane fields (< 0.3 T) applied to switch the magnetizations of the reference and free layers do not reorient the polarizer. Our typical nanopillar device lateral dimensions are between 60 nm and 300 nm and nanopillars are positioned on coplanar waveguides to allow for broadband electrical connections and studies with fast rise time pulses, generated by an arbitrary waveform generator. The switching probability has been determined for variable pulse amplitude and duration, from 0.1 to 10 ns at room temperature.

Characterization of interlayer interactions in magnetic random access memory layer stacks using ferromagnetic resonance

“…Large spin-transfer torques and fast switching have been predicted 1 and MTJ based prototype devices have recently been demonstrated. 3 These results were confirmed in measurements on similar devices in Ref.…”

“…Large spin-transfer torques and fast switching have been predicted 1 and MTJ based prototype devices have recently been demonstrated. 3 These results were confirmed in measurements on similar devices in Ref. 4. Understanding and engineering the magnetic properties as well as the interactions between the magnetic layers plays a key role in optimizing their switching behavior and the magnetic stability of devices.…”

“…[1][2][3] They consist of a spinpolarizing layer with perpendicular magnetization (P) and a magnetic tunnel junction (MTJ) or spin valve with in-plane magnetization orientation of the electrodes (see Fig. 1(a)).…”

Ultrafast spin-transfer switching in spin valve nanopillars with perpendicular anisotropy

“…However, results have been reported for devices with an in-plane free layer and a perpendicular polarizer. [14][15][16] In this letter, we present studies of ultrafast spin-transfer switching in all-perpendicularly magnetized spin-valve nanopillars. We measure the probability of switching for short ͑100 ps-10 ns͒ current pulses as a function of pulse amplitude and duration.…”

Spin-transfer switching of orthogonal spin-valve devices at cryogenic temperatures

“…OST devices exhibit ultrafast switching (sub-ns) and low energy consumption per operation (sub-100 fJ) due to the large initial spin-transfer torque from the perpendicular polarizer. [6][7][8][9][10] Furthermore, these device are well-suited to Josephson junction circuits as they are comprised of magnetic and non-magnetic transition metals and therefore have low impedances (1-30 X).…”