Hans Huebl

Voltage controlled inversion of magnetic anisotropy in a ferromagnetic thin film at room temperature

The control of magnetic properties by means of an electric field is an important aspect in magnetism and magnetoelectronics. We here utilize magnetoelastic coupling in ferromagnetic/piezoelectric hybrids to realize a voltage control of magnetization orientation at room temperature. The samples consist of polycrystalline nickel thin films evaporated onto piezoelectric actuators. The magnetic properties of these multifunctional hybrids are investigated at room temperature as a function of the voltage controlled stress exerted by the actuator on the Ni film. Ferromagnetic resonance spectroscopy shows that the magnetic easy axis in the Ni film plane is rotated by 90° upon changing the polarity of the voltage Vp applied to the actuator. In other words, the in-plane uniaxial magnetic anisotropy of the Ni film can be inverted via the application of an appropriate voltage Vp. Using superconducting quantum interference device (SQUID) magnetometry, the evolution of the magnetization vector is recorded as a function of Vp and of the external magnetic field. Changing Vp allows to reversibly adjust the magnetization orientation in the Ni film plane within a range of approximately 70°. All magnetometry data can be quantitatively understood in terms of the magnetic free energy determined from the ferromagnetic resonance experiments. These results demonstrate that magnetoelastic coupling in hybrid structures is indeed a viable option to control magnetization orientation in technologically relevant ferromagnetic thin films at room temperature.

Observation of extremely slow hole spin relaxation in self-assembled quantum dots

We report the measurement of extremely slow hole spin relaxation dynamics in small ensembles of self-assembled InGaAs quantum dots. Individual spin oriented holes are optically created in the lowest orbital state of each dot and read out after a defined storage time using spin memory devices. The resulting luminescence signal exhibits a pronounced polarization memory effect that vanishes for long storage times. The hole spin relaxation dynamics are measured as a function of external magnetic field and lattice temperature. We show that hole spin relaxation can occur over remarkably long time scales in strongly confined quantum dots (up to similar to 270 mu s), as predicted by recent theory. Our findings are supported by calculations that reproduce both the observed magnetic field and temperature dependencies. The results suggest that hole spin relaxation in strongly confined quantum dots is due to spin-orbit-mediated phonon scattering between Zeeman levels, in marked contrast to higher-dimensional nanostructures where it is limited by valence band mixing.

Electrical detection of coherent 31 P spin quantum states

In recent years, a variety of solid-state qubits has been realized, including quantum dots1,2, superconducting tunnel junctions3,4 and point defects5,6. Owing to its potential compatibility with existing microelectronics, the proposal by Kane7,8—on the basis of phosphorus donors in silicon—has been pursued intensively9,10,11. A key issue of this concept is the readout of the 31P quantum state. Electrical measurements of magnetic resonance have been carried out on single spins12,13, but the statistical nature of these experiments based on random-telegraph-noise measurements has impeded the readout of single spin states. Here, we demonstrate the measurement of the spin state of 31P donor electrons in silicon and the observation of Rabi flops by purely electric means, that is by coherent manipulation of spin-dependent charge-carrier recombination between the 31P donor and paramagnetic localized states at the Si/SiO2 interface. The electron spin information is shown to be coupled through the hyperfine interaction to the 31P nucleus, suggesting that recombination-based readout of nuclear spins is feasible.

Non-local magnetoresistance in YIG/Pt nanostructures

We study the local and non-local magnetoresistance of thin Pt strips deposited onto yttrium iron garnet. The local magnetoresistive response, inferred from the voltage drop measured along one given Pt strip upon current-biasing it, shows the characteristic magnetization orientation dependence of the spin Hall magnetoresistance. We simultaneously also record the non-local voltage appearing along a second, electrically isolated, Pt strip, separated from the current carrying one by a gap of a few 100 nm. The corresponding non-local magnetoresistance exhibits the symmetry expected for a magnon spin accumulation-driven process, confirming the results recently put forward by Cornelissen et al. [1]. Our magnetotransport data, taken at a series of different temperatures as a function of magnetic field orientation, rotating the externally applied field in three mutually orthogonal planes, show that the mechanisms behind the spin Hall and the non-local magnetoresistance are qualitatively different. In particular, the non-local magnetoresistance vanishes at liquid Helium temperatures, while the spin Hall magnetoresistance prevails.

Angle-dependent magnetotransport in cubic and tetragonal ferromagnets: Application to (001)- and "113…A-oriented "Ga,Mn…As

General expressions for the longitudinal and transverse resistivities of single-crystalline cubic and tetragonal ferromagnets are derived from a series expansion of the resistivity tensor with respect to the magnetization orientation. They are applied to strained

Magnon-based logic in a multi-terminal YIG/Pt nanostructure

(mathrm{Ga},mathrm{Mn})mathrm{As}

Passivation of Mn acceptors in GaMnAs

films, grown on (001)- and

Observation of the spin Nernst effect

(113)A

Strong evidence for d-electron spin transport at room temperature at a LaAlO3/SrTiO3 interface

-oriented

Spin Hall magnetoresistance in a canted ferrimagnet

mathrm{GaAs}