High-field magnetic circular dichroism in ferromagnetic InMnSb and InMnAs: Spin-orbit-split hole bands andgfactors

Abstract

Carrier-induced ferromagnetism in magnetic III-V semiconductors has opened up several opportunities for spintronic device applications as well as for fundamental studies of a material system in which itinerant carriers interact with the localized spins of magnetic impurities. In order to understand the hole mediated ferromagnetism, probing the band structure in these material systems is crucial. Here we present magnetic circular dichroism (MCD) studies on MOVPE grown InMnSb and InMnAs, both with the Curie temperatures above 300 K. The measurements were performed on samples with different Mn contents with the excitation energy tuned from 0.92-1.42 eV and external magnetic fields up to 31 Tesla. The large g-factors in these systems allow us to measure the MCD at relatively high temperatures (190 K). These measurements are compared with MCD calculations based on an 8 band Pidgeon-Brown model which is generalized to include the coupling between the electron/hole and the Mn spin in a ferromagnetic state. Comparison of the observed MCD with the theoretical calculations provides a direct method to probe the band structure including the temperature dependence of the spin-orbit split-off gap and g-factors, and to estimate the sp-d coupling constants.

Magnetic field tunability of spin-polarized excitations in a high-temperature magnet

“…Figure 2(d) displays constant energy cuts of the dichroic response vs. magnetic field. The resulting curves display a non-linear progression akin to magnetization, 9,28 although saturation occurs much more slowly due to the local nature of this probe 29 and with some asymmetry compared with M (B) that is accounted for by the metamagnetic transition (discussed below). Optical tracking of M (B) is extremely important for optical data storage and advanced sensing.…”

“…The effects discussed here differ significantly from those that arise in dilute magnetic semiconductors and many of the chalcogenides. The unusual electronic properties of the former are generally attributed to impurity band interactions, 22,28 whereas the latter emanate from strong spin-orbit coupling and include spin-split bands, Rashba splitting, and topologically-protected surface states. 33,34 The character of NiFe 2 O 4 's spin-polarized excitations instead emerges from the two independent magnetic sublattices -an aspect of the crystal, chemical, and electronic structure that will be replicated (in some form) in other spinel ferrites.…”

Ultrafast demagnetization of ferromagnetic semiconductor InMnAs by dual terahertz and infrared excitations

“…According to previous studies, electronic transitions launched by the low-energy photon of the THz pump can be attributed to impurity band transition 18,19 and/ or heavy-hole, light-hole, and split-off valence band transitions. 20,21 However, one cannot exclude that the THz pulse simply pumps intraband transitions, resulting in a heating of free charge carriers in the semiconductor (holes). The sample was in a cold-finger cryostat, and it was cooled down well below T C .…”

“…24, the degree of the demagnetization is determined by laser-induced heating of holes and our work strongly supports this mechanism. Although several interband transitions are expected in the spectral range of the THz pulse, [18][19][20][21] it is safe to assume that the interaction of the pulse with a heavily p-doped semiconductor is described by the Drude theory 25 and the light-matter interaction is dominated by the interaction of the electric field of light with holes. The energy of the THz photon is fully used to increase the kinetic energy (i.e., temperature) of holes, while a substantial part of the energy of the IR photons is used to trigger interband transitions and, thus, increase the potential energy of electrons without any contribution to ultrafast heating of holes.…”

Magnetic field control of charge excitations in CoFe2O4

“…The signal-to-noise ratio was increased by chopping the light; likewise, by passing linearly polarized light through a photoelastic modulator, right-circularly polarized light and left-circularly polarized light were dynamically separated as δ ( t ) = λ /4 sin( ωt ). 43 All signals were separated by lock-in amplifiers. In addition to the epitaxial CoFe 2 O 4 films, we also measured the dichroic response of MgAl 2 O 4 as a function of energy and magnetic field.…”