Nanoscale Zeeman Localization of Charge Carriers in Diluted Magnetic Semiconductor–Permalloy Hybrids

Abstract

We investigate the possibility of charge carrier localization in magnetic semiconductors due to the presence of a highly inhomogeneous external magnetic field. As an example, we study in detail the properties of a magnetic semiconductor-permalloy disk hybrid system. We find that the giant Zeeman response of the magnetic semiconductor in conjunction with the highly non-uniform magnetic field created by the vortex state of a permalloy disk can lead to Zeeman localized states at the interface of the two materials. These trapped states are chiral, with chirality controlled by the orientation of the core magnetization of the permalloy disk. We calculate the energy spectrum and the eigenstates of these Zeeman localized states, and discuss their experimental signatures in spectroscopic probes. , below which they exhibit ferromagnetic order. In the ferromagnetic state, the charge carriers are spin-polarized, making these materials ideal sources of spin-polarized currents. To date, most suggested applications involving DMS are based on this property and therefore are restricted to operation in a range of temperatures T ≪ T c . On the other hand, in the paramagnetic phase T > T c both the III 1−x Mn x V and the more established II 1−x Mn x VI DMSs (which have even lower critical temperatures) show giant Zeeman response to external magnetic fields. In our opinion, this can lead to interesting applications in the paramagnetic state, and consequently at rather elevated temperatures.Convincing experimental evidence for Zeeman splitting in the range of 30 meV for external fields of a few Tesla is provided by photoluminesce spectroscopy studies [2]. Even relatively small external magnetic fields of 0.1 − 0.5 T can easily lead to a 15 meV splitting of electronic energy levels [3]. Comparing this to the vacuum Zeeman splitting of ∼ 0.06 meV (for B = 0.5T ) suggests that the effective gyromagnetic ratio of charge carriers in diluted magnetic semiconductors is g > 500. The origin of this hugely enhanced Zeeman effect is attributed [3] to the strong magnetic coupling i J sp−d ( r − R i ) s · S i between the spin s of the charge carrier and the spins S i of the Mn located at R i . In the paramagnetic state, a small magnetic field B induces a magnetization S i ∼ χ B of the Mn spins, resulting in an effective Zeeman-like s · B coupling between the charge carrier spin and the magnetic field, in addition to the regular Zeeman coupling −g 0 µ B s · B present in non-magnetic semiconductors. The scale of this additional coupling is set by the large exchange energy J sp−d and results in a large effective g-value. This also implies that g(T ) has a strong T-dependence through the magnetic susceptibility, and therefore can be tuned over a large range of values. This scenario is strongly supported by magneto-optical absorption measurements [4] of the Zeeman splitting at the band edge, which clearly exhibits a Brillouin-type dependence on the magnetic field.The presence of giant Zeeman response in DMS implies that a moderate external magnetic fi...

Spintronics: Fundamentals and applications

“…In experiments of 65 At low temperatures (ϳ1 K) Cd 0.95 Mn 0.05 Se has ͉g*͉Ͼ500 (Dietl, 1994), while in n-doped (In,Mn)As ͉g*͉Ͼ100 at 30 K (Zudov et al, 2002). Such large g factors, in the presence of a highly inhomogeneous magnetic field could lead to the charge carrier localization (Berciu and Jankó , 2003). et al (1999) and Jonker et al (2000), at B Ϸ1 T, TϷ4 K, and forward bias, electrons entering from the n contact were almost completely polarized in the spin-down state as they left the spin aligner and were injected across the (II,Mn)VI/AlGaAs interface.…”

Scattering by magnetic nanocylinders and the method of distorted waves in noncollinear fields

“…In [6], the analytic dependences of the magnetization distribution in a disk with a small thickness H were given by…”

Рассеяние На Магнитных Наноцилиндрах И Метод Искаженных Волн В Неколлинеарных Полях

“…Пример конкретного расчета. В работе [6] приведены аналитические зависимости распределения намагниченности в диске малой толщины H:…”