Classical to Quantum - new spintronics concepts
Prof. Dr. Mathias Kläui (Institut für Physik der Universität Mainz)

In our information-everywhere society IT is a major player for energy consumption and novel spintronic devices can play a role in the quest for GreenIT. Reducing power consumption of mobile devices by replacing volatile memory by fast non-volatile spintronic memory could also improve speed and a one-memory-fits-all approach drastically simplifies the microelectronic architecture design.
The best-known memory device is the magnetic hard drive and here conventional magnetic fields are used to excite spin dynamics and manipulate magnetization as necessary for switching of magnetic bits. While this approach is now reasonably well understood and widely employed, it is an energy-hungry process leading to large power dissipation. Furthermore it entails limitations for the speed of magnetic switching as intrinsically the spin dynamics is limited by the precession frequency corresponding to the magnetic field.
Novel low power storage-class memory devices have been proposed, where switching by alternative means, such as spin-polarized currents is used [1] and for this we develop new highly spin-polarized materials [2]. We study the rich physics of the interaction between spin currents, photons and the magnetization [3], and we have used spin-polarized charge carriers and photons to excite spin dynamics and manipulate the magnetization on ultrafast timescales [4].
Finally using alternative concepts with perpendicular excitation [5] and using skyrmions [6,7] might open novel avenues to ultra-low power switching of magnetization with THz read-out [8].

While many of these concepts currently rely on the magnetism of large ensembles and can be described classically, quantum effects play a key role as one downscales the devices. Prominent examples of quantum effects include macroscopic domain wall tunneling, single spin reversal and interference effects of Bose Einstein condensates of magnons.
Finally new detection schemes based on quantum effects, such as nitrogen vacancy centres in diamond can be used for magnetic field detection with unprecedented sensitivity [9].

References:
[1] L. Heyne et al., Phys. Rev. Lett. 105, 187203 (2010); M. Eltschka et al., Phys. Rev. Lett. 105, 056601 (2010).
[2] M. Jourdan et al., Nature Comm. 5, 3974 (2014).
[3] A. Bisig, et al., Nature Comm. 4, 2328 (2013).
[4] B. Pfau et al., Nature Comm. 3, 1100 (2012)
[5] J.-S. Kim et al., Nature Comm. 5, 3429 (2014)
[6] F: Büttner et al., Nature Phys. 11, 225 (2015)
[7] S. Woo et al., Nature Mater. (in press 2016), arxiv:1502.07376
[8] Z. Jin et al., Nature Phys. 11, 761 (2015)
[9] J.-P. Tetienne et al., Science 344, 1366 (2014)