Magneto-elektrische Effecten op Nanometer-nanoseconde-schaal voor Spintronische Toepassingen

Among the technologies that may lead to a paradigm shift with respect to current CMOS technology, spintronics presents several advantages to achieve area and power reduction. The possibility to perform multifrequency processing and the non-volatility of the magnetic materials could provide new functionalities to circuit designers for various applications. However, a major limitation for the realization of spintronic devices is the lack of a scalable and efficient transducer between electric and magnetic domains. Current device concepts are often based on the control of the magnetization by currents, for example via generated magnetic Ørsted fields or more recent effects, such as spin-transfer torque or spin-orbit torque. However, such techniques are typically not very energy-efficient, and it would be very desirable to control the magnetization by electric fields instead. In the last years, magnetoelectricity has seen a renaissance due to technological and theoretical progress. The promise of magnetoelectricity is a large improvement in energy efficiency over current-based approaches. As an example, the energy needed to switch a nanomagnet by spin-transfer torque (~10 fJ) is several orders of magnitude larger than the energy needed to charge a magnetoelectric capacitor (~1 aJ). Thus, electric-field control is an enabling solution for many emerging applications of magnetism, which have been so far rendered uncompetitive due to large power dissipation. The most efficient magnetoelectric systems are layered compounds consisting of piezoelectric and magnetostrictive materials. So far, studies of such magnetoelectric compounds have focused on large scale systems (mm to cm size) with very few reports on micrometer size devices. Moreover, mostly only the low frequency behavior of magneto- electrics has been assessed. Microelectronic applications of magnetoelectricity will however require devices with dimensions in the nanometer range and operate at GHz frequencies, i.e. at (sub-)nanosecond timescales. The main goal of the thesis will thus be the study of nano-scale devices including magnetoelectric compounds and their behavior at GHz frequencies, especially the magnetoelectric excitation of ferromagnetic resonance or spin waves (magnons).