Modulation of the Curie temperature in ferromagnetic/ferroelectric hybrid double quantum wells

Abstract

We propose a ferromagnetic/ferroelectric hybrid double quantum well structure, and present an investigation of the Curie temperature (T c ) modulation in this quantum structure. The combined effects of applied electric fields and spontaneous electric polarization are considered for a system that consists of a Mn δ-doped well, a barrier, and a p-type ferroelectric well. We calculate the change in the envelope functions of carriers at the lowest energy subband, resulting from applied electric fields and switching the dipole polarization. By reversing the depolarizing field, we can achieve two different ferromagnetic transition temperatures of the ferromagnetic quantum well in a fixed applied electric field. The Curie temperature strongly depends on the position of the Mn δ-doped layer and the polarization strength of the ferroelectric well. * Electronic mail: nmikim@dongguk.edu 1The diluted magnetic semiconductor (DMS) has been generally known as one of the promising candidates for spintronic device materials in virtue of the coexistence of ferromagnetic and semiconducting properties in it. Ferroelectric material has also attracted significant interest because of its promising potential in various technological applications, such as binary data storage media in nonvolatile random access memories due to its spontaneous electric polarization. In both research fields, many experimental and theoretical studies have been performed.Because the spintronic devices should ultimately be operated at room temperature, much effort has been focused on increasing the ferromagnetic transition temperature (T c ) of DMS above room temperature. Among many materials, ZnMnO is considered to have T c above 300 K with 5% Mn per unit cell and 3 × 10 20 holes per cm 3 according to a theoretical based on the mean-field approximation. [5,6] The second class of approach is also carrierinduced ferromagnetism as a results of KKR-CPA-LDA (Korringa-Kohn-Rostoker coherentpotential approximation and local density approximation) calculations of the electronic structure of doped DMS alloys. [7,8] The third class of approach suggests the hole hopping mediated ferromagnetism between polarons having strongly localized charge carriers. [9,10] And the fourth one is ferromagnetism due to the ferromagnetic clusters or secondary phases. [11,12] Therefore, it is necessary to decide on a case-by-case basis which mechanism is applicable. In our work, we apply the first class of approach based on the mean-field theory for carrier-induced ferromagnetism in a DMS. [13,14,15] Using ideas based on the dependence of T c of DMS on the spatial distribution of magnetic ions, and envelope functions of carriers at the lowest energy subband in a confining potential [15,16,17], we model a hybrid double quantum well (HDQW) system shown in The lower well Zn 1−y Li y O is the p-type ferroelectric well with spontaneous polarization P.The inverse potential profile of a hole is shown in Fig. 1 We previously demonstrated electric field control of ferromagnetism in Mn δ-do...

Manipulation of spin distribution in double quantum disks with external magnetic field

“…There have been many studies on the control of the spin states in double quantum wells or double quantum dots by using bias voltage [1][2][3]. In our former study, we have demonstrated electric-field-controlled ferromagnetism in Mn δ-doped asymmetric conventional double quantum wells [2] and in hybrid double quantum wells [4]. However, in the previous work, our primary interest was the control of the ferromagnetic transition temperature by either applying electric field or reversing dipole polarization.…”