Local control of spin polarization in a semiconductor by microscale current loops

Abstract

We demonstrate a method to electrically manipulate the spin polarization in a semiconductor on a micrometer length scale and a submicrosecond time scale. A variable magnetic field induced by a microscale current loop magnetizes the Mn2+ ions in a CdMnTe/CdMgTe diluted magnetic semiconductor quantum well, and via sp-d exchange interaction polarizes photogenerated electron-hole pairs. A maximum spin polarization degree of ±8.5% is obtained at 4.2 K without external magnetic field. The induced carrier spin polarization and the thermal heating of Mn2+ spins are resolved spatially and temporally by microphotoluminescence measurements.

Sub‐ns electrical control of spin polarization in a semiconductor by microscale current loops

“…1b) with an amplitude of 120 mA (corresponding to a magnetic field amplitude of about 10 mT [11]) is introduced and magnetizes the Mn 2þ ion spins, and thus, via sp-d exchange interaction, polarizes the spins of optically generated electron-hole pairs. In agreement with former results [8], a positive (negative) current pulse can generate a pronounced positive (negative) carrier spin polarization.…”

“…As the repetition time (35 ns) of the pulse sequence is much shorter than the typical phonon lifetime in the studied system [13], the Mn 2þ spin temperature can be regarded as constant within one period. This explains, why r saturates to a constant value of about AE2.5% instead of continuously decreasing due to thermal heating as observed in former experiments performed on a much longer time scale [8,11].…”

“…by intense optical laser pulses [9,10], on-chip microcoils provide the possibility to electrically control the spin polarization. Due to the low inductivity of such microstructured coils, a frequency range up to the gigahertz (GHz) regime is expected and compared with previous work [7,8], this allows one to study Mn 2þ spin dynamics in a magnetic semiconductor on a sub-nanosecond time scale.…”

“…By introducing a current pulse through the microcoil, a magnetic field pulse is generated, which magnetizes the Mn 2þ ion spins in the DMS QW. Via sp-d exchange interaction, photon-generated carriers can be efficiently polarized due to the giant Zeeman energy splitting between spin-up and spin-down states, which results in the emission of polarized photoluminescence (PL) [8]. Studying the spin polarization by means of time-resolved micro-PL spectroscopy, it is shown that the spin polarization can be switched electrically on a time scale clearly below 1 ns.…”

“…direct generation of spin polarized carriers by circularly polarized optical excitation [2], electrical control via spin-orbit coupling [3] as well as spin resonance experiments in spin blockade geometry [4]. The most straightforward way, however, is to use a magnetic field, either defined by nano-/microferromagnets atop the semiconductor [5,6], or generated by current loops [7,8]. The latter approaches offer the possibility to locally control the spin polarization on a micrometer scale or even below.…”