Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions

Abstract

We demonstrate field and current controlled magnetodynamics in nanocontact spin-torque nano-oscillators (STNOs) based on orthogonal magnetic tunnel junctions (MTJs). We systematically analyze the microwave properties (frequency f , linewidth ∆f , power P , and frequency tunability df /dI) with their physical originsperpendicular magnetic anisotropy (PMA), damping-like and field-like spin transfer torque (STT), and voltage-controlled magnetic anisotropy (VCMA). These devices present several advantageous characteristics: high emission frequencies (f > 20 GHz), high frequency tunability (df /dI = 0.25 GHz/mA), and zero-field operation (f ∼ 4 GHz). Furthermore, a detailed investigation of f (H, I) reveals that df /dI is mostly governed by the large VCMA (287 fJ/(V·m)), while STT plays a negligible role. PACS numbers: Valid PACS appear here a) Correspondence to johan.akerman@physics.gu.se 1 arXiv:1907.10427v2 [physics.app-ph]

Observation of magnetic droplets in magnetic tunnel junctions

“…In contrast to our previous work on an SFL MTJ [27], magnetic droplets are successfully observed in a DFL MTJ here. To clarify the essential difference, we performed micromagnetic simulations to further analyze the stability of the magnetic droplets.…”

“…Therefore, one might expect to observe magnetic droplets in pMTJ-based NC-STNOs. Nevertheless, our previous experiment shows that it is difficult to form a stable droplet in a single-free layer (SFL) MTJ [27]. This may result from the large Zhang-Li torque generated from the interaction between a uniform electric current density and a spatially varying magnetization.…”

“…Therefore, one might expect to observe magnetic droplets in pMTJ based NC-STNOs. Nevertheless, our previous experiment shows that it is difficult to format a stable droplet in a single-free layer (SFL) MTJ29 , which may result from the large Zhang-Li torque induced by the lateral current. In contrast, the DFL pMTJs30 are expected to suppress this large Zhang-Li torque and therefore benefit to format a stable magnetic droplet.Here we experimentally observe and investigate stable magnetic droplets in a DFL pMTJ and find that the droplet enhances the emission power by more than two orders of magnitude with respect to the FMR mode precession in the same device.…”

High-Frequency Microwave Emission of a Trilayer Magnetic Tunnel Junction in the Absence of External Magnetic Bias Field

“…Finally, Figure 4 puts our work in the context of some select achievements reported to date at room temperature and at zero bias field 19,20,22,23 or at a field less than 50 mT 3,16,[36][37][38] . As it is seen the work reported here has the highest zero-field emission frequency to the best of our knowledge.…”

“…These promising devices have developed tremendously over the past years in many aspects for example, enhancing output power [11][12][13][14] and improving linewidth [15][16][17][18] . One of the major attempts has been to eliminate the need of an external bias field [19][20][21][22][23] but still achieving reasonable output microwave frequency in the interest of practical applications. Recently, STNOs have drawn even more attention as building blocks for neural networks in computational tasks for artificial intelligence [24][25][26][27] .…”