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IEEE Magnetics Society
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Tuesday, April 22nd, 2014
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Spin-electronics and -caloritronics are rapidly developing research fields and many new phenomena such as magnetically perpendicular tunnel junctions (P-MTJs) [1, 2], the Spin-Seebeck-Effect (SSE, [3, 4]) and the Tunneling-Magneto-Seebeck-Effect (TMS, [5, 6]) have been observed. Because thermal effects are very important for the Spin-Transfer-Torque (STT) switching of MTJs, this talk will link results on thermally induced currents and voltages in ferromagnets and MTJs with STT-switching of CoFeB/MgO/CoFeB P-MTJs. As an introduction to the field of spin-caloritronics, we first present results on the Longitudinal SSE of semi-conductive nickel ferrites [7]. In this material, the competing Anomalous Nernst Effect (ANE) can be strongly influenced by changing the conductivity of the ferromagnet and thus a direct comparison of LSSE and ANE becomes possible. The second part will discuss the tunneling magnetoresistance (TMR) and the tunneling magneto-Seebeck effect (TMS) detected on magnetic tunnel junctions. We present results on the TMS obtained by two heating methods, discuss time-resolved experiments [8] and the influence of an uncertainty of input parameters such as temperature profiles on the effect. In addition, we demonstrate that an applied bias voltage strongly changes the observed TMS and discuss the results on the base of the electrode’s band-structures. For P-MTJs with ultrathin CoFeB electrodes and MgO barriers with thickness down to 4 monolayers, we discuss the STT-switching mechanisms and demonstrate, that extremely low switching currents for classical Spin-Transfer-Torque switching down to around 2.104A/cm² are possible by controlling the P-MTJ’s temperature. In relation with the thermally driven spin currents, the possibility to achieve sizeable thermally driven STT will be evaluated [2]. [1] S. Ikeda et al., Nat. Mat. 9, (2010) 721 [2] J. C. Leutenantsmeyer, et.al., SPIN 03 (2013) 1350002 [3] K. Uchida, et.al., Nat. Mat. 9,
(2010) 894 [4] K. Uchida, et.al., Appl. Phys.
Lett. 97 (2010) 172505 [5] N. Liebing, et.al., Phys. Rev. Lett. 107 (2011) 177201 [6] M. Walter, et.al., Nat. Mater. 10 (2011) 742 [7] D. Meier, et.al., Phys. Rev. B 87 (2013) 054421. [8] A. Boehnke, et.al., Rev. Sci. Instrum. 84 (2013) 063905. LINK
TO THE PRESENTATION
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