Inspired by the success of FETs in electronics, voltage controlled magnetic anisotropy (VCMA) induced magnetization dynamics has emerged as an important integrant in low-power spintronic devices. In this talk, I will discuss our recent demonstration of VCMA induced parametric resonance excitation for generating magnons with exchange-interaction wavelengths 1. Earlier, we had shown that the growth-induced magnetocrystalline anisotropy can be used for giving rise to a direction-specific magnon scattering 2. This was shown using epitaxy dependent anisotropic damping in (111), (110) and (100) YIG/GGG thin films. However, metallic ferromagnets grown on Si have a better compatibility with CMOS processes. Therefore, we choose CoFeB/MgO junctions, that have emerged to be technologically relevant owing to its high perpendicular magnetic anisotropy, low damping, and high TMR ratios. Following an introduction to our earlier work on YIG, I will focus on the excitation of VCMA induced magnetization dynamics for in-plane magnetized CoFeB/MgO junctions (Fig. 1a), a long-standing limitation of VCMA. This is done using VCMA of interfacial in-plane anisotropy 1, that is induced by magnetic annealing 3. At high powers, VCMA induced parametric resonance is observed (Fig. 1b). The wavelengths of corresponding magnons are estimated to be tuned down to the exchange-interaction length scales using magnetic field, power and frequency of excitation (Fig. 1c). Power dependent parametric pumping amplitudes reveal unique trends at different dynamical excitation regimes (Fig. 1d). The crucial role of excitation frequency in distinguishing VCMA induced magnetization dynamics will be discussed. Finally in Fig 1(e-f), using angular dependent measurements, we prove the presence of electric-field torque from VCMA in both linear and non-linear magnetization dynamics 1. References
1 A. Deka et al., Phys. Rev. Research 4, 023139 (2022). 2 R.M., A. Deka et al., Appl. Phys. Lett. 119, 162403 (2021). (*Equal first author) 3 A. Deka et al., Phys. Rev. B 101 (17), 174405 (2020).

Fig. 1 (a) Illustration of VCMA excitation. (b) Power dependent inverse spin Hall effect voltage V_ISHE. (c) Calculated frequency and magnetic field H_ex dependence on wavength of magnons. (d) Power dependence of V_ISHE at different wavelengths. In-plane angle dependence of V_ISHE amplitudes at (e) uniform and (f) parametric resonances. Lines are fits to equations in Ref. 1.