Structural and functional analysis of nanopillar spin electronic devices fabricated by 3D focused ion beam lithography

Abstract

We discuss the fabrication of nanopillar spin electronic devices from metal multilayered heterostructures, utilizing a novel three-dimensional focused ion beam lithography process. Finite element simulation was performed to optimize the geometry of the nanopillar device and to demonstrate that current flow is perpendicular to the plane within the active region of the device. Clear zero-field current induced magnetization switching is observed in our nanopillar devices at room temperature.

Optical characterization of nonlocal spin transfer torque acting on a single nanomagnet

“…During the milling process, the NiFe/Au layer was protected by a layer of photoresist, which was later removed to allow for optical access. Previous studies on similar devices have reported no evidence of damage to the ferromagnetic layers due to the ion beam bombardment [16]. A schematic diagram of the device and cross section are shown in Figs.…”

“…The CPW was tapered so that the center conductor contained a 20 μm long and 2 μm wide section. In this narrow section a single CPP pillar was fabricated using three-dimensional focused ion beam (3D-FIB) milling [15,16]. The width of the center conductor was first reduced to ß200 nm by milling from the top.…”

“…Because of its high spatial (ß300 nm) and temporal (ß10 ps) resolution, time-resolved scanning Kerr microscopy [12] (TRSKM) has proven to be a powerful magneto-optical tool for contactless detection of magnetization dynamics in individual nanomagnets [13,14]. Here we use TRSKM to characterize the strength of the NL-STT acting on a NiFe free layer (FL) nanomagnet of a two-terminal current perpendicular-to-plane (CPP) spin valve [15,16]. We demonstrate that TRSKM, with carefully optimized spatial resolution and minimal mechanical vibration and drift, can be used as a sensitive, contactless probe of both the dynamic and the quasi-dc magnetization induced by NL-STT.…”

Thickness dependence and the role of spin transfer torque in nonlinear giant magnetoresistance of permalloy dual spin valves

“…By using a focused ion beam nanomachining technique, a number of nanopillar devices were fabricated in the 4-m-wide tracks ͑as described elsewhere͒. 9,10 This was achieved in a four-step process: ͑1͒ narrowing of the 4-m-wide track to a width of ϳ500 nm using a beam current of 150 pA ͓Fig. 1͑a͔͒; ͑2͒ using a reduced beam current of 11 pA, the track width was further reduced to ϳ300 nm; ͑3͒ sample is rotated to an angle of 85°with respect to the ion beam and two side cuts are made, forming a CPP nanopillar device as illustrated in Fig.…”

Nanopillar junctions

“…Because the film multilayer structure is not constrained by the patterning process, either by resist thickness, which would limit stack thickness during lift-off, or by mask erosion, which would limit stack thickness during milling, arbitrarily large thicknesses can be processed using this technique: Leung et al [33] used this process to measure the perpendicular-to-plane spin diffusion length of Cu thin films ( figure 4). Recently, the process has been demonstrated as an effective method of patterning nanopillar devices for studies of Josephson junctions containing various magnetic barriers [34][35][36][37][38] and for CPP magnetoresistance and STT studies [39][40][41]. The primary limitation of the process is the potential for resputtering of material onto the device side walls, a more severe problem than for conventionally ion-milled mesas because of the depth to which material needs to be removed and hence the volume of material that may be resputtered.…”