Observation of electric-field induced magnon fluctuation in nanoscale magnetic tunnel junctions

In quantum science, various physical systems have been proposed as quantum systems that carry information. Nonlinear interactions are essential for revealing the quantum properties of these physical systems. Among these, magnons, the spin-wave quanta, have gained significant attention. This is largely due to their intrinsic rich nonlinearity, which arises from the magnetic interactions in magnets. Another advantage of magnons is the integrability of magnets, which has been developed in spintronics. If a magnon-based quantum system is realized, numerous quantum systems integrated onto a device scale could enable versatile information processing. To this end, it is crucial to acquire the physical states of nonlinearly excited magnons in nanomagnets.

In this presentation, we will present experimental results on magnons generated by parametric excitation and observed as a probability density function of magnon fluctuations in a nanoscale magnetic tunnel junction (MTJ). Parametric excitation is a nonlinear process where periodic modulation of the resonance frequency induces oscillations at half the modulation frequency. To experimentally modulate the magnon resonance frequency, the magnetic anisotropy was modulated by an AC electric field applied to the MTJ, parametrically exciting magnons. They were read out as an AC voltage signal via tunnel magnetoresistance. By obtaining the cosine and sine components of the signal repeatedly, we were able to compose the magnon probability density function.