Skyrmion motion under temperature gradient and application in logic devices

Abstract

Under the presence of temperature gradient (TG) on a nanotrack, it is necessary to investigate the skyrmion dynamics in various magnetic systems under the combined effect of forces due to magnonic spin transfer torque ( μ S T T ) , thermal STT ( τ S T T ), entropic difference ( dS ) , as well as thermal induced dipolar field (DF). Hence, in this work, the dynamics of skyrmions in ferromagnets (FM), synthetic antiferromagnets (SAF), and antiferromagnets (AFM) have been studied under different TGs and damping constants ( α G ). It is observed that α G plays a major role in deciding the direction of skyrmion motion either towards the hotter or colder side in different magnetic structures. Later, FM skyrmion based logic device is proposed that consists of a cross-coupled nanotrack, where the skyrmions on horizontal and vertical nanotrack are controlled by exploiting TG and electrical STT (eSTT), respectively by taking the advantages of thermal induced skyrmion Hall effect (SkHE). The proposed device performs AND and OR logic functionalities simultaneously, when the applied current density is 2 × 10 11 A m - 2 . Moreover, the proposed device is also able to exhibit the half adder functionality by tuning the applied current density to 3 × 10 11 A m - 2 . The total energy consumption for AND and OR logic operation and half adder are 33.63 fJ and 25.06 fJ, respectively. This paves the way for the development of energy-efficient logic devices with ultra-high storage density.

Stable skyrmions in Co/Ni-based nanopillars with perpendicular magnetization anisotropy

“…With the advancements in device processing and control technology, various methods of stimulating and producing skyrmions have diversified, including spin current [27,28], spin Hall effect [29], temperature * Authors to whom any correspondence should be addressed. gradients [30][31][32][33], magnetic anisotropy gradients [34,35], spin wave [36], and electric field [37,38]. Bloch-type skyrmions and Néel-type skyrmions have been observed in B20type non-centrosymmetric compounds and the heavy metal/ferromagnet (HM/FM) bilayer with an interfacial asymmetry [22,[39][40][41][42][43][44][45][46][47].…”

“…This indicates that slightly tilted perpendicular magnetic anisotropy is superior to a perfectly perpendicular magnetic anisotropy in terms of creating stable skyrmions. It is important to note that when considering the influence of thermal fluctuations on the stability of skyrmions, the temperature-dependent parameters (exchange, interfacial DMI, perpendicular anisotropy constants) is crucial [32,33]. Recently, Tomasello et al have developed a theoretical framework to describe the influence of thermal fluctuations on skyrmion stationary by incorporating an appropriate ansatz and the thermal dependence included through the scaling relations of the micromagnetic parameters A, K u , and D with respect to magnetization [53].…”