Orientation of electron spins in hybrid ferromagnet–semiconductor nanostructures

Abstract

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.The spin orientation of electrons is studied in ferromagnet (FM)-semiconductor (SC) hybrid structures composed of a (Ga,Mn)As ferromagnetic layer, which is placed in the direct vicinity of a non-magnetic SC (In,Ga)As quantum well (QW). It is shown that the polarization of carriers in the SC QW is achieved by spin-dependent tunnelling into the magnetized ferromagnetic layer. This leads to dynamical spin polarization of the electrons, which can be directly observed by means of time-resolved photoluminescence. We find that the electron spin polarization grows in time after excitation with an optical pulse and may reach values as large as 30%. The rate of spindependent capture grows exponentially steeply with decreasing thickness of the spacer between ferromagnetic layer and QW, and it persists up to the Curie temperature of the (Ga,Mn)As layer. From time-resolved pump-probe Kerr rotation data, we evaluate a value of only a few μeV for the energy splitting between the electron Zeeman sublevels due to interaction with the ferromagnetic (Ga,Mn)As layer, indicating that the equilibrium spin polarization is negligible.Schematic presentation of electron spin orientation in a semiconductor quantum well (QW) under linearly polarized excitation due to spin-dependent capture of electrons in the ferromagnetic layer (FM). The arrows in the FM box indicate the orientation of the magnetization M. The effect is detected by appearance of a circular polarization degree of photoluminescence after pulsed optical excitation (right). The data are shown for a spacer thickness of 5 nm.

Spin-dependent tunneling in semiconductor heterostructures with a magnetic layer

“…The theoretical description developed further is rather general and can be applied to various semiconductor heterostructures with a similar design. However, in the rest of the paper we will concentrate on a particular heterostructure for which a set of experimental data on time-resolved PL has been obtained allowing the comparison with the theoretical analysis 14,15 . The width of the QW under consideration is a = 10 nm and its depth is controlled by In composition.…”

Спин-Зависимое Туннелирование В Гетероструктурах С Магнитным Слоем

“…Применим развитую теорию для анализа эксперимен-тов по фотолюминесценции с временным разрешением в гетероструктурах на основе In x Ga 1−x As с мелкой леги-рованной КЯ и отдаленным δ-слоем Mn [18,19]. В этих экспериментах наблюдалось сверхбыстрое гашение ФЛ из КЯ после прохождения одиночного неполяризованно-го импульса накачки.…”

“…Излучательная электронно-дырочная ре-комбинация в обсуждаемых структурах является доста-точно медленным процессом с характерным временем τ rad ∼ 10 нс. В [18] показано, что спин неравновесных электронов не успевает полностью исчезнуть за время жизни носителей, тем самым время спиновой релакса-ции оказывается τ s ≥ τ rad . Процесс туннельной безыз-лучательной рекомбинации является быстрым на фоне времен τ s , τ rad , поэтому спин-зависимое туннелирование будет приводить к электронной спиновой поляризации, существующей на временах вплоть до τ s .…”

Indução ótica de magnetização em semicondutores magnéticos

“…O efeito do ferromagnetismo do Mn sobre os elétrons fotoexcitados no poço quântico foram observados em medidas de fotoluminescência e efeito Kerr com resolução temporal em uma amostra com a camada de espaçamento com d e = 10 nm [43,44]. As medidas de fotoluminescência mostraram que, ao aplicar-se um campo magnético normal ao plano da amostra, a luz emitida tem uma polarização circular destra ou sinistra, dependendo da direção do campo.…”

“…O campo magnético foi aplicado na geometria de Voigt. Nossas amostras diferem das estudadas nas referências [42], [43] e [44] pela quantidade de In no poço quântico. Nossas medidas de rotação de Kerr têm máxima amplitude em torno de E = 1, 38 eV (figura 3.11à direita), que coincide com a transição do poço quântico identificada por medidas de PLE das mesmas amostras na referência [48] (figura 3.11à esquerda).…”