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.

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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.

The conductance of a quantum point contact (QPC) shows several features that result from many-body electron interactions. The spin degeneracy in zero magnetic field appears to be spontaneously lifted due to the so-called 0.7 anomaly. Further, the g-factor for electrons in the QPC is enhanced, and a zero-bias peak in the conductance points to similarities with transport through a Kondo impurity. We report here how these many-body effects depend on QPC geometry. We find a clear relation between the enhanced g-factor and the subband spacing in our QPCs, and can relate this to the device geometry with electrostatic modeling of the QPC potential. We also measured the zero-field energy splitting related to the 0.7 anomaly, and studied how it evolves into a splitting that is the sum of the Zeeman effect, and a field-independent exchange contribution when applying a magnetic field. While this exchange contribution shows sample-to-sample fluctuations and no clear dependence on QPC geometry, it is for all QPCs correlated with the zero-field splitting of the 0.7 anomaly. This provides evidence that the splitting of the 0.7 anomaly is dominated by this field-independent exchange splitting. Signatures of the Kondo effect also show no regular dependence on QPC geometry, but are possibly correlated with splitting of the 0.7 anomaly.