Keywords: spintronics, ultra-low-energy, spin-circuits
Summary:Electronics harnessed by electron's spin-based counterpart, so-called spintronics, has been widely studied in the context of nanomagnets. I will speak on the recent developments on ultra-low-energy, area-efficient, and fast spintronic devices, in particular on electric field-induced magnetization switching in multiferroic magnetoelectric devices. It has been shown that electric field-induced magnetization switching in strain-mediated piezoelectric-magnetostrictive multiferroic composites dissipates a miniscule amount of energy of ~1 attojoule (aJ) in sub-nanosecond switching delay at room-temperature and experimental efforts are emerging on such front [1,2]. Using such multiferroic devices, digital computing , analog signal processing capability with transistor-like high-gain region , scaling trends , separating read and write units , and Landauer limit of energy dissipation  have been studied. Also, interface-coupled multiferroic heterostructures , dynamics in multiferroic materials , and energy dissipation in giant spin Hall devices  have been analyzed. For technological suitability, apart from being energy-efficient, spin-devices must be area-efficient (~10 nm lateral dimensions) and possess fast switching speed. I will show that antiferromagnetically exchange-coupled nanomagnets can be employed to harness area-efficiency and faster switching speed. Although there has been enormous progress in the field of spintronics and nanomagnetics in recent years with the advent of new materials and phenomena, it remained a formidable challenge to integrate them into functional devices and evaluate their potential. I will speak on the developments of spin-circuits that can be useful for analyzing complex spin-devices and predicting new device designs. Different components can be represented as 4-component (one for charge and 3 for spin-vector) circuit elements in general and we can utilize the traditional circuit theory considering spin relaxation. Such representation, apart from being necessary for large-scale circuits, is useful for understanding and proposing experiments e.g., on this topic, I will speak on spin pumping induced inverse spin Hall voltages in giant spin Hall materials and topological insulators .  K. Roy, Ultra-low-energy Electric field-induced Magnetization Switching in Multiferroic Heterostructures, SPIN 6, 1630001 (2016); SPIN 3, 1330003 (2013). News: Switching up spin, Nature 476, 375, (2011) DOI:10.1038/476375c; AIP news, PhysicsWorld, NanoTechWeb.  K. Roy et al., Appl. Phys. Lett. 99, 063108 (2011); Phys. Rev. B 83, 224412 (2011); J. Appl. Phys. 112, 023914 (2012); Scientific Reports 3, 3038 (2013).  K. Roy, SPIN 3, 1330003 (2013); Appl. Phys. Lett. 103, 173110 (2013); Appl. Phys. Lett. 104, 013103 (2014).  K. Roy, Proc. SPIE Nanoscience (Spintronics VII) 9167, 91670U (2014); MRS Proc. 1691, DOI: 10.1557/opl.2014.730 (2014).  K. Roy, IEEE Tran. Magn. 51, 2500808 (2015).  K. Roy, Scientific Reports 5, 10822 (2015).  K. Roy, J. Phys. Condens. Matter 26 , 492203 (2014).  K. Roy, J. Phys. D: Appl. Phys. 47, 252002 (2014).  K. Roy, Europhys. Lett. 108, 67002 (2014).  K. Roy, J. Phys. D: Appl. Phys. 47, 422001 (2014).  K. Roy, Spin Circuit Representation of Spin Pumping, in APS March Meeting, Session Y28.12 (2015); in APS March Meeting, Session K18.4 (2016); in EMN Meeting on Magnetic Materials (invited), Hawaii, Mar 22; on Spintronics (invited), Las Vegas, Oct 12 (2016).