New perspective on symmetry breaking in an antiferromagnetic chain: Spin-selective transport and NDR phenomenon

Abstract

The primary requirement for achieving spin-selective electron transfer in a nanojunction possessing a magnetic system with zero net magnetization is to break the symmetry between the up and down spin sub-Hamiltonians. Circumventing the available approaches, in the present work, we put forward a new mechanism for symmetry breaking by introducing a bias drop along the functional element. To demonstrate this, we consider a magnetic chain with antiparallel alignment of neighboring magnetic moments. The junction is modeled within a tight-binding framework, and spin-dependent transmission probabilities are evaluated using wave-guide theory. The corresponding current components are obtained through the Landauer-Büttiker formalism. Selective spin currents, exhibiting a high degree of spin polarization, are obtained over a wide bias region. Moreover, the bias-dependent transmission profile exhibits negative differential resistance (NDR), another important aspect of our study. We examine the results under three different potential profiles, one linear and two non-linear, and in each case, we observe a favorable response. This work may offer a new route for designing efficient spintronic devices based on bias-controlled magnetic systems with vanishing net magnetization.

Figures (11)

• Figure 1: (Color online). Schematic of the junction setup where a one-dimensional antiferromagnetic chain with zero net magnetization is clamped between two nonmagnetic 1D electrodes, namely, source (S) and drain (D). The red arrows are the magnetic moments directed along the $+Z$ and $-Z$ directions alternatively.
• Figure 2: (Color online). Bias drop along the AFM chain as a function of site index. Three different potential profiles are shown, where one is linear and the other two are nonlinear.
• Figure 3: (Color online). Spin-specific density of states (blue $\rightarrow$ up spin, red $\rightarrow$ down spin) as a function of energy at two biased conditions where (a) $V=0$ and (b) $V=3\,$V. The bias drop is considered following prof-1, as illustrated in Fig. \ref{['fig:f2']}.
• Figure 4: (Color online). Up (blue) and down (red) spin transmission probabilities as a function of energy at three distinct biased conditions, where (a) $V=0$, (b) $V=1.7\,$V, and (c) $V=3.7\,$V. The bias drop is the same as taken in Fig. \ref{['fig:f2']}.
• Figure 5: (Color online). Up and down spin currents as a function of bias voltage, considering a linear bias drop along the clean AFM chain, at two different Fermi energies, where (a) $E_F=0$ and (b) $E_F=1.25\,$eV. In each sub-figure, two small black circles are drawn to indicate the peak and valley currents, in one of the NDR regions.