Spin-valley polarization and tunneling magnetoresistance in monomer, dimer, and trimer magnetic silicene superlattices.

Monomer, dimer and trimer semiconductor superlattices are an alternative for bandgap engineering due to the possibility of duplicate, triplicate, and in general multiply the number of minibands and minigaps in a specific energy region. Here, we show that monomer, dimer, and trimer magnetic silicene superlattices (MSSLs) can be the basis for tunable magnetoresistive devices due to the multiplication of the peaks of the tunneling magnetoresistance (TMR). In addition, these structures can serve as spin-valleytronic devices due to the formation of two well-defined spin-valley polarization states by appropriately adjusting the superlattice structural parameters. We obtain these conclusions by studying the spin-valley polarization and TMR of monomer, dimer, and trimer MSSLs. The magnetic unit cell is structured with one seed A with positive magnetization, and one, two, or three seeds B with variable magnetization. The number of B seeds defines the monomer, dimer, and trimer superlattice, while its magnetic orientation positive or negative the parallel (PM) or antiparallel magnetization (AM) superlattice configuration. The transfer matrix method and the Landauer-Büttiker formalism are employed to obtain the transmission and transport properties, respectively. We find multiplication of TMR peaks in staircase fashion according to the number of B seeds in the superlattice unit cell. This multiplication is related to the multiplication of the minibands which reflects as multiplication of the descending envelopes of the conductance. We also find well-defined polarization states for both PM and AM by adjusting asymmetrically the width and height of the barrier-well in seeds A and B.

Tunneling magnetoresistance and spin-valley polarization of aperiodic magnetic silicene superlattices.

Magnetic silicene superlattices (MSSLs) are versatile structures with spin-valley polarization and tunneling magnetoresistance (TMR) capabilities. However, the oscillating transport properties related to the superlattice periodicity impede stable spin-valley polarization states reachable by reversing the magnetization direction. Here, we show that aperiodicity can be used to improve the spin-valley polarization and TMR by reducing the characteristic conductance oscillations of periodic MSSLs (P-MSSLs). Using the Landauer-Büttiker formalism and the transfer matrix method, we investigate the spin-valley polarization and the TMR of Fibonacci (F-) and Thue-Morse (TM-) MSSLs as typical aperiodic superlattices. Our findings indicate that aperiodic superlattices with higher disorder provide better spin-valley polarization and TMR values. In particular, TM-MSSLs reduce considerably the conductance oscillations giving rise to two well-defined spin-valley polarization states and a better TMR than F- and P-MSSLs. F-MSSLs also improve the spin-valley polarization and TMR, however they depend strongly on the parity of the superlattice generation.