Self-sustained Magnetoelectric Oscillations in Magnetic Resonant Tunneling Structures

Abstract

The dynamic interplay of transport, electrostatic, and magnetic effects in the resonant tunneling through ferromagnetic quantum wells is theoretically investigated. It is shown that the carrier-mediated magnetic order in the ferromagnetic region not only induces, but also takes part in intrinsic, robust, and sustainable high-frequency current oscillations over a large window of nominally steady bias voltages. This phenomenon could spawn a new class of quantum electronic devices based on ferromagnetic semiconductors. DOI: 10.1103/PhysRevLett.101.077202 PACS numbers: 85.75.ÿd, 72.25.Dc, 73.63.Hs, 75.50.Pp Ferromagnetism of diluted magnetic semiconductors (DMSs), such as GaMnAs [1], depends strongly on the carrier density [2][3][4][5]. The possibility to tailor space charges in semiconductors by bias or gate fields naturally suggests similar tailoring of magnetic properties of DMSs. While early experiments have indeed succeeded in generating ferromagnetism in DMSs electrically or optically [6,7], ramifications of the strong carrier-mediated ferromagnetism in the transport through DMS heterostructures are largely unexplored.In resonant tunneling through a quantum well not only the tunneling current, but also the carrier density in the well is sensitive to the alignment of the electronic spectra in the leads and in the well. If the quantum well is a paramagnetic DMS, the resulting transport is influenced by the spin splitting of the carrier bands in the well, as observed experimentally [8]. The magnetic resonant diodes are prominent spintronic devices [9], proposed for spin valves and spin filtering [10,11], or for digital magnetoresistance [12]. If the quantum well is made of a ferromagnetic DMS [13,14], resonant tunneling conditions should influence magnetic ordering as well. It has already been predicted that the critical temperature T c of the well can be strongly modified electrically [15][16][17]. Here we show that the magnetic ordering affects back the tunneling current, in a peculiar feedback process, leading to interesting dynamic transport phenomena.Conventional nonmagnetic resonant-tunneling diodes can exhibit subtle intrinsic bistability and terahertz current oscillations [18][19][20][21] resulting from the nonlinear feedback of the stored charge in the quantum well. Interesting phenomena occur also in multiple quantum wells and superlattices, in which electric field domains form whose dynamics leads to current oscillations in the kHz-GHz range [22]. This effect has been exploited for spindependent transport by incorporating paramagnetic quantum wells [23,24].In this Letter we introduce a realistic model of a selfconsistently coupled transport, charge, and magnetic dynamics and apply it to generic asymmetric resonant diodes with a ferromagnetic quantum well to predict selfsustained, stable high-frequency oscillations of the electric current and quantum well magnetization. We formulate a qualitative explanation for the appearance of these magnetoelectric oscillations. In essence, ferromagnetic quantum ...

Electron spin relaxation in paramagnetic Ga(Mn)As quantum wells

“…1,2,3,4,5,6,7 Many new device conceptions and functionalities based on these materials are proposed, and the material properties together with the underlying physics are extensively studied. 4,8,9,10,11,12,13,14,15,16 Specifically, ferromagnetic Ga 1−x Mn x As has been used as a highly efficient source to inject spin polarization into GaAs 17 and magnetic tunneling junctions based on ferromagnetic Ga 1−x Mn x As can achieve very high magnetoresistance. 18 Besides, the ability to detect the magnetic moment via Hall measurements 4,19 and to control it via gate-voltage 20 and laser radiation 21 opens the way for incorporating optoelectronics with magnetism.…”

Perspectives in spintronics: magnetic resonant tunneling, spin-orbit coupling, and GaMnAs

“…These studies revealed that the exchange splitting of the carriers subbands essentially depends (i) on the spin polarization of the particle density in the well and (ii) on the overlap of the subband wave function with the magnetic impurity density profile. Based on these findings we recently proposed that the combined nonlinear feedback of Coulomb and magnetic interaction can lead to self-sustained high-frequency oscillations of the tunneling current and the quantum well magnetization over a large window of nominally dc-bias voltages [20], as illustrated in the upper panel of Fig. 2.…”

“…Based on these findings we recently proposed that the combined nonlinear feedback of Coulomb and magnetic interaction can lead to self-sustained high-frequency oscillations of the tunneling current and the quantum well magnetization over a large window of nominally dc-bias voltages [20], as illustrated in the upper panel of Fig. 2.…”

Phase diagrams and switching of voltage and magnetic field in dilute magnetic semiconductor nanostructures

“…Recently, spin transport through dilute magnetic semiconductor (DMS) diodes 7 and multi‐quantum well structures (MQWS) has been analyzed 8–10, especially the nonlinear features of the current (hysteresis, multistability) as a function of the external voltage. Under strong dc voltage bias V , electric field domains are formed in MQWS due to the interplay between electron–electron interaction and resonant tunneling 8.…”