SCIENCE SPIN-OFFS

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Electric-field tunable spin waves in PMN-PT/NiFe heterostructure: experiment and micromagnetic simulations

Slawomir Zietek, Jakub Checinski, Marek Frankowski, Witold Skowronski, Tomasz Stobiecki
(Submitted on 14 Oct 2016)

We present a comprehensive theoretical and experimental study of voltage-controlled standing spin waves resonance (SSWR) in PMN-PT/NiFe multiferroic heterostructures patterned into microstrips. A spin-diode technique was used to observe ferromagnetic resonance (FMR) mode and SSWR in NiFe strip mechanically coupled with a piezoelectric substrate. Application of an electric field to a PMNPT creates a strain in permalloy and thus shifts the FMR and SSWR fields due to the magnetostriction effect. The experimental results are compared with micromagnetic simulations and a good agreement between them is found for dynamics of FMR and SSWR with and without electric field. Moreover, micromagnetic simulations enable us to discuss the amplitude and phase spatial distributions of FMR and SSWR modes, which are not directly observable by means of spin diode detection technique.

https://arxiv.org/abs/1610.04500

FIG. 4: Spatial distribution maps of (a) FFT amplitude of FMR mode,(b)FFTphaseofFMRmode,(c)FFTamplitudeofSSWR 3rd mode, (d) FFT phase of SSWR 3rd mode

On a polished PMN-PT (0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3) [011] oriented piezoelectric substrate, a 20nmofNi80Fe20 wasdepositedusingmagnetronsputtering. In order to apply electric ?eld perpendiculary to thepiezoelectricsubstrate,thebottomsideofthecrystal was covered by a Ti 5 nm/Au 50 nm layer. Microstrips of 6.7 µm width and 90 µm length were fabricated using electron beam lithography and ion-beam etching. Angular depenence of SD-FMR apmlitudes was measured in a four-pole electromagnet probe station, which enables application of an arbitrary ?eld vector in the sample plane. FMR spectra were measured using (SD) technique similarly to Ref. 16. An RF current of 10 dBm power at frequencies in range form 3 GHz to 8 GHz was passed trough the ferromagnetic microstrip. Magnetization oscillations induced by this current, due to the AMR effect, cause small changes of resistance in microwave frequency range, which mixes with RF current and givea a raise of SD voltage. This voltage was measured using a lock-in technique during the magnetic ?eld sweep at various magnetic ?eld angles ?H. A top and bottom layer of PMN-PT piezoelectric substrate were previously covered by 50nm of Au, excluding inconsiderable area where micro-devices were fabrication. In order to generate in-plane stress in piezoelectric substrate, a 100 V was applied from additional voltage source to top and bottom metallic layer, simillary as in Ref. 18.


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