Light and Electric Field Control of Ferromagnetism in Magnetic Quantum Structures

Abstract

A strong influence of illumination and electric bias on the Curie temperature and saturation value of the magnetization is demonstrated for semiconductor structures containing a modulationdoped p-type Cd0.96Mn0.04Te quantum well placed in various built-in electric fields. It is shown that both light beam and bias voltage generate an isothermal and reversible cross-over between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design. The observed behavior is in quantitative agreement with the expectations for systems, in which ferromagnetic interactions are mediated by the weakly disordered two-dimensional hole liquid.Soon after the discovery of carrier-controlled ferromagnetism in Mn-doped III-V [1] and II-VI [2] semiconductor compounds, it has become clear that these systems offer unprecedented opportunities to exploit the powerful methods developed for tuning carrier densities in semiconductor quantum structures, in order to control the magnetic characteristics in these systems [2,3,4,5,6]. Such a control opens new prospects for information storage and processing, as well as it makes it possible to examine the behavior of strongly correlated systems as a function of externally controllable parameters. In the case of III-V magnetic semiconductors, Koshihara et al.[3] detected an enhancement of ferromagnetism by illumination of an (In,Mn)As/GaSb heterostructure, an effect assigned to the presence of an interfacial electric field that drives the photo-holes to the magnetically active (In,Mn)As layer. More recently, Ohno et al.[6] demonstrated that a gate voltage of ±125 V changes the Curie temperature T C by about 1 K in a field-effect transistor structure containing an (In,Mn)As quantum well (QW).In the case of II-VI diluted magnetic semiconductors (DMS), Mn does not introduce any carriers. Hence, holemediated ferromagnetic interactions can be induced by modulation-doping of heterostructures [7]. Due to the valence band structure, T C is typically lower in II-VI than in III-V DMS. At the same time, however, it may be expected [2,5] that, owing to the small background hole density, the strength of the carrier mediated ferromagnetic interactions can be tuned over a wider range in II-VI than in III-V DMS.In this paper, we present photoluminescence (PL) studies of modulation-doped p-type (Cd,Mn)Te QW. The (Cd,Zn,Mg)Te barriers are doped either p-or n-type, so that p-i-p or p-i-n structures are formed. The QW in these systems are ferromagnetic below about 3 K. We show that, depending of the sample layout, the ferromagnetism is either destroyed or enhanced during illumination by photons with energy greater than the band gap of the barrier material. In both cases, the switching process is isothermal and reversible. Moreover, we demonstrate that the reverse biasing of the p-i-n diode by a voltage smaller than 1 V turns the ferromagnet into a paramagnetic material. Importantly, this strong effect of light and electric field can be readily explained by considering the distributi...

Spintronics: Fundamentals and applications

“…It was also shown that the magnetic field generated by passing the current through a CPP giant magnetoresonance device could produce roomtemperature magnetization reversal (Bussmann et al, 1999). In the context of ferromagnetic semiconductors additional control of magnetization was demonstrated optically, by shining light (Koshihara et al, 1997;Boukari et al, 2002;Oiwa et al, 2002) and electrically, by applying gate voltage (Ohno, Chiba, et al, 2000;Boukari et al, 2002;Park et al, 2002) to perform switching between the ferromagnetic and paramagnetic states.…”

Semi-conducteurs magnétiques dilués

“…Dans ce cas, la mesure de l'aimantation locale dans le puits est obtenue par spectroscopie optique : une aimantation spontanée induit un effet Zeeman géant (et donc une décomposition de la raie de luminescence en deux raies, voir figure 4) en l'absence de champ appliqué [4].…”

Ferromagnetic semiconductor heterostructures

“…However, this antiferromagnetic coupling can be overcompensated by ferromagnetic interactions mediated by band holes [4][5][6]. In Ill-V compounds, Mn atoms when substituting trivalent metals supply both localized spins and holes, so Photon energy they enhance the magnitude of spontaneous magnetisation in the caseofa p-i-ndiode [10], as shown in Fig. 2.…”

“…2: Effect of temperature (a), bias voltage (b), and illumination (c) on photoluminescence of structure consisting of modulation doped p-(Cd.Mn)Te quantum well and n-type barrier. Zero-field line splitting (marked by red arrows) and shift on lowering temperature witness the appearance'of a ferromagnetic ordering at low temperatures (a), which does not show up if the quantum well is depleted from the holes by reverse bias of the pion diode (b),The low-temperature splitting is enhanced by additional illumination by white light which increases the hole concentration in the quantum well (after Boukari et al [10]). …”

“…Such tuning capabilities of the materials systems in question were put into the evidence in (In,Mn)As/(Al,Ga)Sb [8,9] and modulation doped p-(Cd,Mn)Te/(Cd,Mg,Zn)Te [5,10] heterostructures, as depicted in Figs. 1 and 2.…”