Giant spin-torque diode sensitivity in the absence of bias magnetic field

Abstract

Microwave detectors based on the spin-torque diode effect are among the key emerging spintronic devices. By utilizing the spin of electrons in addition to charge, they have the potential to overcome the theoretical performance limits of their semiconductor (Schottky) counterparts. However, so far, practical implementations of spin-diode microwave detectors have been limited by the necessity to apply a magnetic field. Here, we demonstrate nanoscale magnetic tunnel junction microwave detectors, exhibiting high-detection sensitivity of 75,400 mV mW−1 at room temperature without any external bias fields, and for low-input power (micro-Watts or lower). This sensitivity is significantly larger than both state-of-the-art Schottky diode detectors and existing spintronic diodes. Micromagnetic simulations and measurements reveal the essential role of injection locking to achieve this sensitivity performance. This mechanism may provide a pathway to enable further performance improvement of spin-torque diode microwave detectors.

Detection of concealed targets using spintronic microwave sensor

“…Table 1 summarizes the reflectivity R(ω) and the refractive index n(ω) calculated at 2.5GHz frequency by Eqs. (4,5) and compared to the experimental data published by Duque et al [34]. For the TATB and TNT materials, good agreement is obtained between our calculated values and the experimental data.…”

“…[6]. The rectification voltage has been measured using various horn antennas covering a wide range of microwave frequencies (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Although the absolute value of V r varies with frequency, its power dependence is always linear for all measured frequencies.…”

“…[1][2][3][4] It has been found that under microwave radiation a dc voltage can be generated in such spintronic devices not only at the ferromagnetic resonance, but also in the absence of any external applied magnetic field that is far from the resonance condition. The in-depth understanding of the spin dynamics in the ferromagnetic nanostructure allows the sensitivity (which is characterized by the ratio between the produced dc voltage and the incident microwave power) to be improved more than four orders of magnitude, from the earliest report [1] of 1.4 mV/mW to the latest report [4] of 74,500 mV/mW, that can compete with the commercial semiconductor Schottky diode detectors. Different from the resonant microwave detection occurring in the vicinity of the ferromagnetic resonance, where an external magnetic field is usually required, the non-resonant detection allows spintronic devices to perform broadband microwave measurements in the absence of any external applied magnetic field and may move spintronic devices towards practical microwave applications such as microwave imaging.…”

“…Different from the resonant microwave detection occurring in the vicinity of the ferromagnetic resonance, where an external magnetic field is usually required, the non-resonant detection allows spintronic devices to perform broadband microwave measurements in the absence of any external applied magnetic field and may move spintronic devices towards practical microwave applications such as microwave imaging. [4][5][6][7][8] Microwave radiation can propagate through large distances in space and has modest attenuation when passing through physical barriers such as clothing, plastics, soil, sand, and rocks. Thus microwaves can interact with subsurface structures in addition to structures on the surface of the material.…”

Microwave holography using a magnetic tunnel junction based spintronic microwave sensor

“…This subsurface imaging that can "see" the invisible allows embedded defects and/or concealed threats to be non-destructively detected, making microwave imaging attractive for applications in non-destructive testing, 1,2 medical screening, 3,4 and counterterrorism. 5,6 Recent development of spintronics has attracted intensive interest for microwave applications, [7][8][9][10][11][12][13] resulting in about four orders of magnitude enhancement of the sensitivity in spintronic microwave detectors based on the magnetic tunnel junction (MTJ) 14,15 as well as the rapid microwave phase detection using MTJ devices. 16 At the beginning of 2014, a Japanese group in Osaka University 14 found at some special conditions (d.c. bias current, external bias magnetic field, and resonant frequency), spintronic device's sensitivity could be as high as 12 000 mV/mW, while the value was only 1.4 mV/mW in the first report in 2005.…”