Caitlin Feeser

Ferromagnetic InMnSb multi-phase films study by aberration-corrected (scanning) transmission electron microscopy

In this work we report a structural and compositional study of ferromagnetic In0.78Mn0.22Sb films correlated to the magnetic properties as determined by superconducting quantum interference device magnetometer. The epilayers grown by metalorganic vapor phase epitaxy on GaAs(001) substrates showed two active magnetic components with Curie temperatures of approximately 300 K and in excess of 570 K. Secondary phases driven by the high manganese concentration (10 at. %) were identified by high-resolution (scanning) transmission electron microscopy imaging and energy dispersive X-ray spectroscopy. Most of the Mn was found to be incorporated in metallic manganese nanoprecipitates surrounded by an InMnSb matrix with Mn at 1 at. % concentration. The origin of the two Curie temperatures of the film is associated with the presence of three magnetic components: hexagonal MnSb nanoprecipitates, non-stoichiometric MnAsSb, and the InMnSb matrix.

Spin-dependent magnetotransport in a p-InMnSb/n-InSb magnetic semiconductor heterojunction

The spin-dependent transport properties in p-InMnSb/n-InSb magnetic semiconductor heterojunctions are presented. A positive junction giant magnetoresistance is observed from 75 to 298 K. The magnetoresistance is attributed to conduction via two spin channels resulting from p-d exchange interaction. The magnetoconductance of the heterojunction and its magnetic field dependence are well-described by a two-band model where the bands are spin-polarized. At 75 K and zero field, the spin polarization in the alloy is 90% and decreases to 48% at 298 K. The large spin polarization indicates that InMnSb should be suitable for spin-based transistors that operate at room temperature.

Structural and magnetic properties of epitaxial In1–xMnxSb semiconductor alloys with x > 0.08

High temperature ferromagnetic In1−xMnxSb semiconductor alloys with a Curie temperature (TC) above 400 K were investigated. Alloys with x ranging from 0.08 to 0.22 deposited by metalorganic vapor phase epitaxy were examined. X-ray diffraction indicated alloys are primarily two phase consisting of a zinc blende InMnSb solid solution and hexagonal MnSb precipitates. Transmission electron microscopy analysis confirmed the presence of hex-MnSb nanoprecipitates as well as the presence of the additional minority phases Mn3Sb, metallic Mn, and MnAs1−xSbx. Magnetization measurements indicate that the alloy films are ferromagnetic, showing clear hysteresis in field dependent measurements from 5 to 400 K. Magnetization values as high as 47 emu/cm3 for an alloy with x = 0.22 were measured at room temperature. Irreversibility is observed between field-cooled and zero-field-cooled magnetization curves that is attributed to inhomogeneous magnetic order arising from randomly distributed ferromagnetic nanoprecipitates. T...

Mn doped InSb studied at the atomic scale by cross-sectional scanning tunneling microscopy

We present an atomically resolved study of metal-organic vapor epitaxy grown Mn doped InSb. Both topographic and spectroscopic measurements have been performed by cross-sectional scanning tunneling microscopy (STM). The measurements on the Mn doped InSb samples show a perfect crystal structure without any precipitates and reveal that Mn acts as a shallow acceptor. The Mn concentration of the order of ∼1020 cm−3 obtained from the cross-sectional STM data compare well with the intended doping concentration. While the pair correlation function of the Mn atoms showed that their local distribution is uncorrelated beyond the STM resolution for observing individual dopants, disorder in the Mn ion location giving rise to percolation pathways is clearly noted. The amount of clustering that we see is thus as expected for a fully randomly disordered distribution of the Mn atoms and no enhanced clustering or second phase material was observed.

Characterization of InMnSb epitaxial films for spintronics

Dilute (III, Mn)V ferromagnetic magnetic semiconductors have potential applications in spintronic devices as magnetic field sensors, spin transistors and reconfigurable logic devices. For such applications ferromagnetism at room temperature is a practical requirement. Previous work has shown that In1−xMnxSb films grown on GaAs (100) substrates by atmospheric pressure metalorganic vapour phase epitaxy were single phase and had high temperature ferromagnetism for Mn concentrations up to 2%. Here we present a study of InMnSb thin films at higher Mn concentration (10 at%) showing ferromagnetic properties at room temperature. Aberration corrected and analytical (scanning) transmission electron microscopy techniques were used to study the structure and elemental distribution of the In1−xMnxSb/GaAs system. The crystalline quality of the film and the presence of phase separation is evaluated in the context of a cluster-mediated ferromagnetism model.

Time Resolved Spectroscopy in Narrow Gap MOVPE Grown Ferromagnetic Semiconductors

We report on time resolved experiments that provide insight into the time scales and the nature of the interactions in ferromagnetic InMnAs and InMnSb. Theoretical calculations are performed using an 8 band k·p model including non-parabolicity, band-mixing, and the interaction of magnetic Mn impurities with itinerant electrons and holes.

Time-resolved spectroscopy of MOVPE-grown III-Mn-V ferromagnetic semiconductors

In this work we investigate carrier dynamics of narrow gap ferromagnetic alloys grown by MOVPE. We determine the intraband and interband relaxation times in these material systems where the samples are excited with photon energies above the band gap of InMnAs and InMnSb films. Our results are important for understanding the electronic states and the relaxation mechanisms in these ferromagnetic materials.

Time Resolved Spectroscopy of MOVPE Grown Narrow Gap Ferromagnetic Semiconductors

We report on time resolved differential transmission experiments to provide insight into both the time scales and the nature of the microscopic interactions and carrier dynamics in MOVPE grown ferromagnetic InMnAs and InMnSb. Theoretical calculations of the electronic structure for InMnAs are performed using an 8 band k⋅p model which includes non‐parabolicity of the conduction bands; strong band‐mixing of the valence bands; as well as coupling of Mn impurities to the electrons and holes. Our preliminary theoretical results explain the sign change in the differential transmission signal as a function of probe wavelength.

Probe of coherent and quantum states in narrow-gap based semiconductors with strong spin-orbit coupling

In light of the growing interest in spin-related phenomena and devices, there is now renewed interest in the science and engineering of narrow gap semiconductors. In this work, time resolved spectroscopy of InSb-based parabolic multi-quantum wells and narrow gap ferromagnetic alloys grown by MOVPE, have been pursued. In addition, in this study, we report on CR experiments carried out on the ferromagnetic InMnAs film, on which clear resonance signals have been successfully observed in high magnetic fields. Investigation of the electronic structure of III-Mn-V alloys by techniques such as the cyclotron resonance can shed important light on the origin of ferromagnetism and the p-d exchange interaction in III-Mn-V systems. Our results are important for understanding the electronic and magnetic states in these material systems.