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Electrically controlled magnetic memory and programmable logic based on graphene/ferromagnet hybrid structures

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3 Author(s)
Y. G. Semenov ; Dept. of Electrical & Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911 ; J. M. Zavada ; K. W. Kim

In the present study we analyze a novel design for a low-power-consuming, non-volatile magnetic switch that is based on the unique properties of the graphene layers placed in the interface between ferromagnetic dielectric layers (FDLs). In particular, the structure under consideration consists of three FDLs which are coupled through monolayer graphene (MLG) and bilayer graphene (BLG) layers as shown in Fig. 1. The coupling effect is represented in terms of effective magnetic fields Hn= ??n/2M0, where M? is a total magnetic moment of free FDL and ??? is a thermodynamic potential for MLG (n=l) or BLG (n=2) electrons that interact with proximate FDLs. Here ??? = NG2 fn(??) where N is the total graphene primitive cells at the interface with the FDL, G is the energy of graphene electrons FDL exchange interaction, and ?? is the electro-chemical potential shift. The crucial property of H? lies in significant dependence of the effective fields on graphene chemical potential ? [1]. Figure 2 highlights such dependence for |H?| ~f? and |H2|~f2 and their sum Htot assuming identical values of ? for MLG and BLG. Since the graphene doping shifts the chemical potential by the magnitude ?o, the charge neutrality point corresponds to Htot(?o)=0. Note that directions of H? and H2 are opposite and that Htot and Mb=Mt are antiparallel for ??=?-?0<0 (as depicted in Fig. 1) or parallel for ??>0. This effect can be utilized for magnetization Mf switching and writing an information bit through changes in ? produced by gate voltage variation. The coercivity Hc secures the stability of the magnetization. The strength of Hc is limited by the inequality Hc< Htot(|??|~0.1). Consequently, there is a range of exchange bias fields that guarantees the reversal of Mf (see Fig. 3). Readout can be readily performed by measurement of the BLG conductivity that depends on the magnetization orientations of proximate FDLs. In Fig. 4, the principle of the switching operation is illustrated for me- mory.

Published in:

2009 Device Research Conference

Date of Conference:

22-24 June 2009