N°16 - 23 September 2016 - HOMODYNE-DETECTED FERROMAGNETIC RESONANCE OF IN-PLANE MAGNETIZED NANOCONTACTS: COMPOSITE SPIN-WAVE RESONANCES AND THEIR EXCITATION MECHANISM

Masoumeh Fazlali, Mykola Dvornik, Ezio Iacocca,* Philipp Dürrenfeld, and Mohammad Haidar
Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden
 
Johan Åkerman
Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden;
Materials Physics, School of ICT, KTH Royal Institute of Technology, 164 40 Kista, Sweden;
and NanOsc AB, Electrum 205, 164 40 Kista, Sweden
 
Randy K. Dumas
Department of Physics, University of Gothenburg, 412 96 Gothenburg, Sweden
and NanOsc AB, Electrum 205, 164 40 Kista, Sweden
 
*Present address: Department of Applied Mathematics, University of Colorado, Boulder, Colorado 80309-0526, USA and Department of Applied Physics,Division for Condensed Matter Theory, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
 

This work provides a detailed investigation of the measured in-plane field-swept homodyne-detected ferromagnetic resonance (FMR) spectra of an extended Co/Cu/NiFe pseudo-spin-valve stack using a nanocontact (NC) geometry. The magnetodynamics are generated by a pulse-modulated microwave current, and the resulting rectified dc mixing voltage, which appears across the NC at resonance, is detected using a lock-in amplifier. Most notably, we find that the measured spectra of the NiFe layer are composite in nature and highly asymmetric, consistent with the broadband excitation of multiple modes. Additionally, the data must be fit with two Lorentzian functions in order to extract a reasonable value for the Gilbert damping of the NiFe. Aided by micromagnetic simulations, we conclude that (i) for in-plane fields the rf Oersted field in the vicinity of the NC plays the dominant role in generating the observed spectra, (ii) in addition to the FMR mode, exchange-dominated spin waves are also generated, and (iii) the NC diameter sets the mean wave vector of the exchange-dominated spin wave, in good agreement with the dispersion relation.

Physical Review B, 93, 134427 (2016)

DOI:http://dx.doi.org/10.1103/PhysRevB.93.134427

Fig. 1: (a) The normalized measured mixing voltage Vmix and (b) the normalized simulated magnetization precession amplitude for the three NC diameters as a function of the applied in-plane magnetic field. (c) Spatial maps of the magnetization precession amplitude (top row and phase (bottom row) simulated for a D = 160 nm NC diameter taken at the fields corresponding to the main peak and its ½ and ¼ heights [as shown by the corresponding black symbols in (b)]. Propagating spin waves are clearly seen for the two lowest fields.