Tunable Conductance of Magnetic Nanowires with Structured Domain Walls

Abstract

We show that in a magnetic nanowire with double magnetic domain walls, quantum interferences result in spin-split quasistationary states localized mainly in between the domain walls. Spin-flipassisted transmission through the domain structure increases strongly when these size-quantized states are tuned on resonance with the Fermi energy, e.g. upon varying the distance between the domain walls which results in resonance-type peaks of the wire conductance. This novel phenomena is shown to be utilizable to manipulate the spin density in the domain vicinity. The domain walls parameters are readily controllable and the predicted effect is hence exploitable in spintronic devices.PACS numbers: 75.60. Ch,75.70.Cn,75.75.+a The discovery of the giant magnetoresistance [1] and its rapid and diverse industrial utilizations sparked major efforts in understanding and exploiting spin-dependent transport phenomena. In particular, new perspectives of even broader importance are anticipated from combining semiconductor technology with nanoscale fabrication techniques to produce magnetic semiconducting materials and control precisely the spins of the carriers. At the heart of this new field that is now termed "semiconductor spintronics" [2] is the understanding of the transport properties of a magnetic domain wall (DW), which is a region of inhomogeneous magnetization in between two domains of homogeneous (different) magnetizations. Thick (or adiabatic) DWs occurring in bulk metallic ferromagnets have an extension much larger than the carriers Fermi wave length and are largely irrelevant for the resistance [3]. In contrast, a series of recent experiments on magnetic nanostructures, and particularly nanowires, revealed that the magnetoresistance in the presence of DWs can be as large as several hundreds [4,5] or even thousands [6,7] of percents. These observations have decisive consequences in so far as DWs are controllable efficiently by applying a magnetic field [8] and can also be steered by a spin-polarized electric current [9], meaning that the magnetoresistance of the structure containing DW is controllable via an electric field.The interpretation of the huge magnetoresistance of DWs observed in magnetic semiconductor (in the ballistic quantum regime) relies on the relative sharpness of DWs on the scale set by the wavelength of carriers (electrons or holes) [10,11,12,13,14]. In such a situation spin-dependent scattering of carriers from DWs is greatly enhanced. In this paper we predict the formation of spin quantum wells and the occurrence of a novel effect in magnetic semiconductor nanowires with double DWs: By pinning one of the DWs at a constriction, one can control the location of the second DW. The spin-dependent transmission and reflection of carriers waves from the first and the second DW and the quantum interference between these waves lead to the formation of spin-split quasistationary states and hence the double DWs act in effect as a penetrable "spin quantum well" (located in between the two DWs). Lifetimes and...

Current-induced interactions of multiple domain walls in magnetic quantum wires

“…In such a situation, the DW interaction increases due to the strongly enhanced DW scattering. [35][36][37][38] The interaction energy ͑Fig. 1͒ depends periodically on the DWs mutual angle 0 and distance z 0 , which results in an oscillating motion of the DW along the axis z as well as an oscillating direction of DW polarization.…”

Electronic and magnetic properties of basic nanosystems of early 3d transition metals (Sc, Ti, V, Cr, and Mn)

“…The studies on magnetism in low dimensional systems have since been fortified [3,4] and have proved very informative and useful. The quantum conductance [5] of magnetic NWs could be tuned with structured domain walls [6] and hence the predicted effect may be exploited for spintronics. Magnetic NWs are of potential interest also for sensors and magnetic recording [7], and could be used in biosciences also as artificial cilia transducers [8].…”

Local Current Injection into Mesoscopic Superconductors for the Manipulation of Quantum States

“…Preparation and manipulation of discrete quantum states are crucial for applications of quantum physics in nanoscale electronics, particularly switching devices and memories. The needed quantum states with discrete conductance levels, and the external control of those, have been recently realized in solid electrolytes [1], graphene [2] (both voltage biased), light-driven molecular switches [3], and magnetic nanowires tuned by magnetic field [4]. With a similar goal, the current-driven processes started to attract immense attention since the demonstration that the magnetization state of a nanomagnet can be influenced directly by electrical current [5].…”