Fully Electrical Read-Write Device Out of a Ferromagnetic Semiconductor

Abstract

We report the realization of a read-write device out of the ferromagnetic semiconductor (Ga,Mn)As as the first step to fundamentally new information processing paradigm. Writing the magnetic state is achieved by current-induced switching and read-out of the state is done by the means of the tunneling anisotropic magneto resistance (TAMR) effect. This one bit demonstrator device can be used to design a electrically programmable memory and logic device.PACS numbers: 75.50. Pp, 75.30.Gw, At present memory and logic fabrication are two fully separated architectures [1,2]. While bulk information storage traditionally builds on metallic ferromagnets, logic makes use of gateability of charge carriers in semiconductors. Combining storage and processing in a single monolithic device not only would solve current technical issues such as the heat dissipation generated by transferring information between the two architectures, but also offer the possibility of a fully non-volatile information processing system. Here we present a read-write device which can be used as one element of an electrically programmable logic gate. Our structure is made from the ferromagnetic semiconductor (Ga,Mn)As, which exhibits carrier-induced ferromagnetism at low temperatures [3][4][5]. The 70 nm thick (Ga,Mn)As layer is grown by lowtemperature molecular beam epitaxy (MBE) on a GaAs buffer and substrate. Due to the lattice mismatch to the GaAs buffer the (Ga,Mn)As layer is compressively strained and therefore has its magnetic easy axes in the plane perpendicular to the growth direction [6]. After growth of the MBE layers, and without breaking vacuum, the sample is transferred to a UHV evaporation chamber, and 3x0.9 nm of aluminum is deposited on top of the (Ga,Mn)As layer. After deposition, each of the three Al layers is oxidized by keeping it for 8 hours in a 200 mBar oxygen atmosphere. The wafer is then covered by 5 nm Ti and 30 nm Au. The ferromagnetic transition temperature of the (Ga,Mn)As layer is 61 K as determined by SQUID (superconducting quantum interference device). Figure 1 shows the read-write device. It consists of four nanobars which are connected to a circular center region. The structure is defined using electron beam lithography and chemical assisted ion beam etching (CAIBE). The nanobars are 200 nm wide and 2 µm long. After patterning, the Ti/Au and aluminum oxide (Alox) layer are removed from the bars and each nanobar is contacted by Ti/Au contacts using a lift-off technique. The Alox/Ti/Au layer on top of the 650 nm central disk remains on the structure and acts as a read-out tunnel contact. For this purpose, the Au layer on the central disk is contacted by a metallic air-bridge [7]. Small notches are patterned at the transition from the nanobars to the central disk and serve to pin down domain walls.Thin films of unpatterened compressively strained (Ga,Mn)As exhibit an in-plane biaxial magnetic anisotropy at low temperatures. The bars connected to the central disk are aligned with their length parallel to the magnetic easy...

Ferromagnetic Order at Room Temperature in Monolayer WSe2 Semiconductor via Vanadium Dopant

“…[ 1–8 ] The most typical example is Mn‐doped GaAs, which exhibit a gate‐controlled magnetic hysteresis, yielding a large number of spintronic devices such as spin‐injection sources and memory devices. [ 2,9–13 ] Nevertheless, the Curie temperature ( T c ) of ferromagnetic transition in magnetic semiconductors is scarcely accessible to room‐temperature (RT), precluding the use of these materials to practical implementations. [ 2–5,14 ] The ferromagnetic state in magnetic metal‐doped oxides and nitrides is available at RT but is localized to aggregated metal oxide/nitride nanoparticles without a long‐range magnetic order.…”

Energy dissipation and switching delay in stress-induced switching of multiferroic nanomagnets in the presence of thermal fluctuations

“…With realistic ramp rates (rate at which stress on the magnet is ramped up or down) a magnet can be switched with ∼100% probability with a (thermally averaged) switching delay of ∼0.5 ns and (thermally averaged) energy dissipation ∼200 kT at room-temperature. This is very promising for "beyond-Moore's law" ultra-low-energy computing [11][12][13] . Our simulation results show the following: (1) a fast ramp and a sufficiently high stress are required to switch the magnet with high probability in the presence of thermal noise, (2) the stress needed to switch with a given probability increases with decreasing ramp rate, (3) if the ramp rate is too slow, then the switching probability may never approach 100% no matter how much stress is applied, (4) the switching probability increases monotonically with stress and saturates at ∼100% when the ramp is fast, but exhibits a non-monotonic dependence on stress when the ramp is slow, and (5) the thermal averages of the switching delay and energy dissipation are nearly independent of the ramp rate if we always switch with the critical stress, which is the minimum value of stress needed to switch with non-zero probability in the presence of noise.…”

Stochastic Current-Induced Magnetization Switching in a Single Semiconducting Ferromagnetic Layer

“…In spin electronics, a large variety of stimuli has been demonstrated to be efficient in manipulating a magnetic state, such as spin polarized currents [1][2][3], ultrafast laser pulses [4], and electric fields [5,6], thereby opening challenging questions on the physical processes involved in magnetization excitations [7][8][9] and reversal [2,[10][11][12][13][14][15][16][17]. In particular, current-induced magnetization reversals in nanopillars or domain-wall motion in tracks originate from a spin transfer torque (STT) [18,19] exerted on local magnetic moments by accumulated out-of-equilibrium carrier spins.…”

“…In particular, current-induced magnetization reversals in nanopillars or domain-wall motion in tracks originate from a spin transfer torque (STT) [18,19] exerted on local magnetic moments by accumulated out-of-equilibrium carrier spins. STT effects [20][21][22] have been explored in metallic [10,13,16] and in semi-conducting [2,14,15] magnetic multilayer nanopillar structures. While most of these experiments aim at understanding current-induced magnetization reversal in a deterministic way, reports on stochastic reversal remain scarce [11,12,17].…”