Underlying Mechanisms and Tunability of the Anomalous Hall Effect in NiCo₂O₄ Films with Robust Perpendicular Magnetic Anisotropy

Abstract

Their high tunability of electronic and magnetic properties makes transition‐metal oxides (TMOs) highly intriguing for fundamental studies and promising for a wide range of applications. TMOs with strong ferrimagnetism provide new platforms for tailoring the anomalous Hall effect (AHE) beyond conventional concepts based on ferromagnets, and particularly TMOs with perpendicular magnetic anisotropy (PMA) are of prime importance for today's spintronics. This study reports on transport phenomena and magnetic characteristics of the ferrimagnetic TMO NiCo2O4 (NCO) exhibiting PMA. The entire electrical and magnetic properties of NCO films are strongly correlated with their conductivities governed by the cation valence states. The AHE exhibits an unusual sign reversal resulting from a competition between intrinsic and extrinsic mechanisms depending on the conductivity, which can be tuned by the synthesis conditions independent of the film thickness. Importantly, skew‐scattering is identified as an AHE contribution for the first time in the low‐conductivity regime. Application wise, the robust PMA without thickness limitation constitutes a major advantage compared to conventional PMA materials utilized in today's spintronics. The great potential for applications is exemplified by two proposed novel device designs consisting only of NCO films that open a new route for future spintronics, such as ferrimagnetic high‐density memories.

Ultralow Electric Current-Assisted Magnetization Switching due to Thermally Engineered Magnetic Anisotropy

“…In this way, the resistance value when the current completely suppresses magnetism is substituted into the R−T curve, and the corresponding temperature should be close to Curie temperature. For 10 and 32 nm NCO thin films, T c is about 390 and 430 K, respectively, which is close to the literature report, 27,43 and the reliability of this temperature correspondence is also verified.…”

“…Perpendicular magnetic anisotropy (PMA) materials are of great importance for spintronics because of their unique advantages including higher device density and much smaller switching current in STT- and SOT-based devices. − In application, compared with traditional PMA materials used in spintronics, the stubborn PMA of transition metal oxides (TMOs) without thickness limitation constitutes a major advantage. − The high adjustability of electronic and magnetic properties makes TMOs with PMA very attractive in both fundamental sciences and practical applications. , Metallic NiCo 2 O 4 (NCO) with strong PMA and high spin polarization is highly desirable for the development of low-power, high-speed spintronics including MRAMs and magnetic field sensors. − In addition, the magnitude of magnetoresistive based on NCO nanostructures can be further tuned by disorder and strain, which can be exploited for design of versatile devices with multifunctionality . Recently, the concept of thermally assisted MRAM has been experimentally verified by taking advantage of current pulses. ,,,− However, there are few reports on current controllable PMA of TMOs, which is a key element in building out-of-plane magnetic tunnel junctions for MRAM.…”