Electrical detection of spin pumping due to the precessing magnetization of a single ferromagnet Costache, M. V.; Sladkov, M.; Watts, S. M.; van der Wal, C. H.; van Wees, B. J.

We demonstrate on-chip resonant driving of large cone-angle magnetization precession of an individual nanoscale permalloy element. Strong driving is realized by locating the element in close proximity to the shorted end of a coplanar strip waveguide, which generates a microwave magnetic field. We used a microwave frequency modulation method to accurately measure resonant changes of the dc anisotropic magnetoresistance. Precession cone angles up to 9 0 are determined with better than one degree of resolution. The resonance peak shape is well-described by the Landau-Lifshitz-Gilbert equation. PACS numbers:The microwave-frequency magnetization dynamics of nanoscale ferromagnetic elements is of critical importance to applications in spintronics. Precessional switching using ferromagnetic resonance (FMR) of magnetic memory elements 1 , and the interaction between spin currents and magnetization dynamics are examples 2 . For device applications, new methods are needed to reliably drive large angle magnetization precession and to electrically probe the precession angle in a straightforward way.We present here strong on-chip resonant driving of the uniform magnetization precession mode of an individual nanoscale permalloy (Py) strip. The precession cone angle is extracted via dc measurement of the anisotropic magnetoresistance (AMR), with angular resolution as low as one degree. An important conclusion from these results is that large precession cone angles (up to 9 0 in this study 3 ) can be achieved and detected, which is a key ingredient for further research on so-called spin-battery effects 4,5 . Moreover, measurements with an offset angle between the dc current and the equilibrium direction of the magnetization show dc voltage signals even in the absence of applied dc current, due to the rectification between induced ac currents in the strip and the timedependent AMR.Recently we have demonstrated the detection of FMR in an individual, nanoscale Py strip, located in close proximity to the shorted end of a coplanar strip waveguide (CSW), by measuring the induced microwave voltage across the strip in response to microwave power applied to the CSW 6 . However, detailed knowledge of the inductive coupling between the strip and the CSW is required for a full analysis of the FMR peak shape, and the precession cone angle could not be quantified. In other recent experiments, dc voltages have been measured in nanoscale, multilayer pillar structures that are related to the resonant precessional motion of one of the magnetic layers in the pillar 7,8 . In one case the dc voltage is generated by rectification between the microwave current applied through the structure and its time-dependent giant magnetoresistance (GMR) effect 8 . Similar voltages FIG.

Electromagnetically induced transparency with an ensemble of donor-bound electron spins in a semiconductor Sladkov, Maksym; Chaubal, A. U.; Bakker, M. P.; Onur, A. R.; Reuter, D.; Wieck, A. D.; van der Wal, C. H.

We measured ferromagnetic resonance of a single submicron ferromagnetic strip, embedded in an on-chip microwave transmission line device. The method used is based on detection of the oscillating magnetic flux due to the magnetization dynamics, with an inductive pick-up loop. The dependence of the resonance frequency on applied static magnetic field agrees very well with the Kittel formula, demonstrating that the uniform magnetization precession mode is being driven.Recent discoveries of novel phenomena in mesoscopic systems containing nanomagnets pave the way to new spintronics devices 1,2,3 . Brataas et al. 4 proposed a new application of ferromagnetic resonance (FMR), a so-called spin battery. In such a device, a spin current flows into a paramagnetic metal from its interface with a precessing ferromagnet, which is resonantly driven with an rf magnetic field. A number of experiments 5,6,7,8,9,10 , have been used to measure FMR on thin ferromagnetic films or on ensembles of small ferromagnets. This work measured rf-power transmission or absorption with a coplanar waveguide with ferromagnetic material on top of it, or with ferromagnetic material in a microwave cavity.

We present the design and operation of a fiber-based cryogenic confocal microscope. It is designed as a compact cold-finger that fits inside the bore of a superconducting magnet, and which is a modular unit that can be easily swapped between use in a dilution refrigerator and other cryostats. We aimed at application in quantum optical experiments with electron spins in semiconductors and the design has been optimized for driving with, and detection of optical fields with well-defined polarizations. This was implemented with optical access via a polarization maintaining fiber together with Voigt geometry at the cold finger, which circumvents Faraday rotations in the optical components in high magnetic fields. Our unit is versatile for use in experiments that measure photoluminescence, reflection, or transmission, as we demonstrate with a quantum optical experiment with an ensemble of donor-bound electrons in a thin GaAs film.