Field-domain spintronics in magnetic semiconductor multiple quantum wells

A three barrier resonant tunneling structure in which the two quantum wells are formed by a magnetic semiconductor is theoretically investigated. Self-consistent numerical simulations of the structure predict giant magnetocurrent in the resonant bias regime as well as significant current spin polarization for a considerable range of applied biases. The requirements for large magnetocurrent are spin resolved resonance levels as well as asymmetry ͑spatial or magnetic͒ of the coupled quantum wells. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2402878͔Semiconductor spintronics offers additional functionalities to the existing electronics technology by combining charge and spin properties of the current carriers. 1 Spin dependent resonant tunneling in double barrier heterostructures has been investigated both experimentally and theoretically with a magnetic quantum well ͑QW͒ made of semimetallic ErAs ͑Refs. 2 and 3͒ or dilute magnetic semiconductors ͑DMSs͒ such as GaMnAs ͑Refs. 4-9͒ or ZnMnSe ͑Refs. 10 and 11͒. Such diodes have been used as spin filters or spin detectors and effective injection of spin-polarized electrons into semiconductors has been demonstrated by employing interband tunneling devices based on GaMnSb. 12,13 A theoretical investigation of resonant tunneling through a nonmagnetic double barrier structure, e.g., AlAs/ GaAs/ AlAs, sandwiched between two bulk ferromagnetic DMSs, e.g., GaMnAs, shows a tremendous enhancement of the tunneling magnetoresistance ͑TMR͒ for low voltages if the thickness of the QW is properly tuned. 14 The effect has been demonstrated to be as high as 10 000% for generic parabolic bands and when including a more realistic kp band structure model still very high TMRs of about 800% have been obtained. 14 Such structures have already been grown and studied experimentally. 4,15,16 Here we propose to use magnetic resonant tunneling diodes ͑RTDs͒ comprising coupled magnetic QWs and three nonmagnetic barriers, as spintronic devices offering large magnetocurrents ͑MCs͒. Corresponding nonmagnetic three barrier structures have been experimentally studied, [17][18][19][20] while electric field domain formation in magnetic multiple QWs was theoretically investigated in Ref. 21. The magnetic three barrier structure allows to establish parallel ͑P͒ and antiparallel ͑AP͒ magnetization configurations and to observe MC. The QWs are assumed to be made of ferromagnetic semiconductors. 5,22 We consider here generic parabolic n-type ferromagnetic QWs, though one expects to observe similar effects in coupled p-type ferromagnetic QWs. Several suitable n-type ferromagnetic semiconductors have been reported: 1 HgCr 2 Se 4 , 23 CdCr 2 Se 4 , 24 CdMnGeP 2 , 25 or most promising ZnO and GaMnN; 22,27 the latter two are believed to exhibit room temperature ͑RT͒ ferromagnetism. To be specific we perform our numerical simulations for GaMnNbased structures.However, it is still controversial if the reported RT ferromagnetism in transition metal doped GaN and ZnO is due to non-resolved precipitates or n...

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confidence: 99%

Resonant tunneling magnetoresistance in coupled quantum wells

Ertler

Fabian

2006

“…The interplay between the nonlinearity of the current-voltage characteristics and the exchange interaction produces interesting spin dependent features 15 : multistability of steady states with different polarization in the magnetic wells, time-periodic oscillations of the spin-polarized current and induced spin polarization in nonmagnetic wells by their magnetic neighbors, among others. The high sensitivity of these systems to external fields points out to their potential application as magnetic sensors 15 .…”

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confidence: 99%

“…The high sensitivity of these systems to external fields points out to their potential application as magnetic sensors 15 .…”

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confidence: 99%

“…for spin s = ±1/2, and B, J sd , N M n , and T eff are the external magnetic field, the exchange integral, the density of magnetic impurities and an effective temperature which accounts for Mn interactions, respectively 15,16 . We model spin-flip scattering coming from spin-orbit or hyperfine interaction by means of a phenomenological scattering time τ sf , which is larger than impurity and phonon scattering times: τ scat =h/γ < τ sf .…”

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confidence: 99%

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Multi-quantum-well spin oscillator

Bonilla

Escobedo

Carretero

et al. 2007

A dc voltage biased II-VI semiconductor multiquantum well structure attached to normal contacts exhibits self-sustained spin-polarized current oscillations if one or more of its wells are doped with Mn. Without magnetic impurities, the only configurations appearing in these structures are stationary. Analysis and numerical solution of a nonlinear spin transport model yield the minimal number of wells (four) and the ranges of doping density and spin splitting needed to find oscillations.

“…Much has been done to exploit the possibilities offered by these materials in diverse spintronic device concepts. 2 For instance, in magnetic resonant tunneling diodes 3-9 ͑m-RTDs͒ or magnetic multiple quantum well diodes, 10,11 the transmission can strongly depend on the spin orientation of the electrons at the Fermi level, which allows to use the diodes as spin filters and detectors. The quantum well of RTDs can be formed either by a ferromagnetic semiconductor [12][13][14] or by dilute magnetic semiconductors ͑DMSs͒, 15 which exhibit giant g factors.…”

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confidence: 99%

Proposal for a digital converter of analog magnetic signals

Ertler¹,

Fabian²

2006

A device which converts analog magnetic signals directly into digital information is proposed. The device concept is based on the monostable-bistable transition logic element, which consists of two resonant tunneling diodes ͑load and driver͒ connected in series and employs the monostable to bistable working point transition of the circuit. Using a magnetic resonant tunneling diode as the driver allows to control the resulting working point of the bistable region by an external magnetic field leading either to high or low output voltage of the circuit, effectively realizing what could be called digital magnetoresistance. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2374800͔Since the realization of magnetic III-V semiconductors 1 substantial progress has been made in pushing the transition temperature to even higher values, strongly nurturing the hope for technically applicable room temperature magnetic semiconductors in the near future. Much has been done to exploit the possibilities offered by these materials in diverse spintronic device concepts. 2 For instance, in magnetic resonant tunneling diodes 3-9 ͑m-RTDs͒ or magnetic multiple quantum well diodes, 10,11 the transmission can strongly depend on the spin orientation of the electrons at the Fermi level, which allows to use the diodes as spin filters and detectors. The quantum well of RTDs can be formed either by a ferromagnetic semiconductor 12-14 or by dilute magnetic semiconductors ͑DMSs͒, 15 which exhibit giant g factors. Magnetic devices provide the interesting opportunity of realizing nonvolatile reprogrammable logic elements. A nonvolatile ferromagnet/superconductor switch based on Andreev reflections was proposed in Ref. 16.Nonmagnetic RTDs have been used for multiple valued logic and multiple logic functions with multiple input and/or output, 17 due to their specific N-shaped current-voltage ͑IV͒ characteristics and their extremely high-speed potential. In 1993 Maezawa and Mizutani proposed the monostablebistable transition logic element ͑MOBILE͒. 18 The concept was extended to multistable elements 19,20 and applications to ultrahigh-speed analog to digital converters were demonstrated. 21 The MOBILE device consists of two nonmagnetic RTDs, a load and a driver, which are connected in series. In this letter we demonstrate that MOBILE circuits with m-RTDs can be used as digital converters of analog magnetic signals by realizing digital magnetoresistance ͑DMR͒: for a continuous change of the magnetic field through a controlled threshold the output electrical characteristics such as voltage exhibit discrete jumps. A nice related effect of the MOBILE has been realized by Hanbicki et al.: 22 a nonmagnetic driver RTD is shunted with a metallic giant magnetoresistance resistor, allowing for current modulations through the RTD. This fascinating phenomenon makes DMR-MOBILEs serious candidates for magnetic reading devices. Figure 1 shows the schematic circuit diagram for a DMR-MOBILE, in which the driver is a m-RTD. The basic concept of the operation ...