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 11.08.2011   Карта сайта     Language По-русски По-английски
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Экология
Электротехника и обработка материалов
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Статистика публикаци


11.08.2011

Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection





Journal name:

Nature

Volume:

476,

Pages:

189–193

Date published:

(11 August 2011)

DOI:

doi:10.1038/nature10309


Received


Accepted


Published online


Corrected online







Modern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts1. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields2, 3 and currents4, 5, 6, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization7. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to8. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlOx interface layers9, 10. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors11, 12, as well as with the torque induced by the spin Hall effect in the platinum layer13, 14. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technology.





Figures at a glance


left


  1. Figure 1: Device schematic and current-induced switching.


    a, Hall cross geometry. Black and white arrows indicate the ‘up’ and ‘down’ equilibrium magnetization states of the cobalt layer, respectively. b, Scanning electron micrograph of the sample and electric circuitry used in the measurements. and represent the two terminals for the Hall voltage measurements. c, Mz measured by the anomalous Hall resistance as a function of applied field, B. d, Mz measured after the injection of positive (black squares) and negative (red circles) current pulses of amplitude Ip = 2.58mA. The data are reported during a single sweep of B, corresponding to the solid line in c. e, Schematic of the pulse sequence and magnetization measurements. In both c and d, B is applied at θ = 92°, parallel to the current direction (φ = 0°). The 2° offset with respect to the ideal in-plane direction is used to define the residual component Bz unambiguously.




  2. Figure 2: Switching efficiency as a function of current amplitude.


    a, b, Mz measured after injection of positive (black squares) and negative (red circles) current pulses of amplitude Ip = 1.57mA (a) and Ip = 1.94mA (b). Filled symbols indicate data recorded during a +Bright arrowB sweep and open symbols indicate data recorded during a −Bright arrow+B sweep, as shown by the arrows. The solid and dashed lines in a represent Mz as a function of field. c, Switching efficiency as a function of pulse amplitude and applied magnetic field. Region I: conventional field-induced magnetization reversal occurs at B = Βc. Region II: assisted reversal. Red triangles indicate the minimum external field required to reverse Mz parallel to Bz. Region III: pulse-induced switching. Black triangles indicate the minimum field at which positive current pulses reverse the magnetization antiparallel to Bz. The maximum field at which switching is observed (blue open squares) coincides with the coercivity of the dot.




  3. Figure 3: Dependence of switching on applied field direction.


    a, Diagrams representing Mz reversal regions, showing the intensity and orientation of the applied magnetic field, B, at constant current (Ip = 3.3mA). Colours indicate the switching sense: red, upwards; blue, downwards. Filled symbols show the coercive field at each angle. When B is aligned with the current (φ = 0°), the switching areas extend throughout the entire bistability region delimited by Βc, with the exception of a narrow area near zero field. As B is rotated away from the current, the sizes of the switching areas gradually decrease. When B is perpendicular to the current (φ = 90°), switching disappears and is replaced by random nucleation. b, Azimuthal dependence of the switching efficiency at constant current (Ip = 3.1mA, θ = 87°). Open symbols represent the largest field against which switching is observed; filled symbols show the coercive field. The dashed line is a sine function. c, Directions of the effective switching field, BSz, relative to j, the in-plane magnetization component (Mx) induced by B, and the Rashba field, BR. The magnetization switches from ‘up’ to ‘down’ for j>0, B>0 and j<0, B<0, and from ‘down’ to ‘up’ for j>0, B<0 and j<0, B>0.




  4. Figure 4: Prototype of a reconfigurable ferromagnetic switch.







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А Б В Г Д Е Ё Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ы Ь Э Ю Я
  • Chen Wev .  honorary member of ISSC science council

  • Harton Vladislav Vadim  honorary member of ISSC science council

  • Lichtenstain Alexandr Iosif  honorary member of ISSC science council

  • Novikov Dimirtii Leonid  honorary member of ISSC science council

  • Yakushev Mikhail Vasilii  honorary member of ISSC science council

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