Nguyen Thanh Tu

High-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb

We show high-temperature ferromagnetism in heavily Fe-doped ferromagnetic semiconductor (Ga1-x,Fex)Sb (x = 23% and 25%) thin films grown by low-temperature molecular beam epitaxy (LT-MBE). Our crystal structure analysis by scanning transmission electron microscopy (STEM) indicates that the (Ga1-x,Fex)Sb thin films maintain the zinc-blende crystal structure at x = 25%. The intrinsic ferromagnetism was confirmed by magnetic circular dichroism (MCD) spectroscopy and anomalous Hall effect (AHE) measurements. The Curie temperature reaches 300 K and 340 K for x = 23% and 25%, respectively, which are the highest values reported so far in intrinsic III-V ferromagnetic semiconductors.

(Ga,Fe)Sb: A p-type ferromagnetic semiconductor

A p-type ferromagnetic semiconductor (Ga1−x,Fex)Sb (x = 3.9%–13.7%) has been grown by low-temperature molecular beam epitaxy (MBE) on GaAs(001) substrates. Reflection high energy electron diffraction patterns during the MBE growth and X-ray diffraction spectra indicate that (Ga,Fe)Sb layers have the zinc-blende crystal structure without any other crystallographic phase of precipitates. Magnetic circular dichroism (MCD) spectroscopy characterizations indicate that (Ga,Fe)Sb has the zinc-blende band structure with spin-splitting induced by s,p-d exchange interactions. The magnetic field dependence of the MCD intensity and anomalous Hall resistance of (Ga,Fe)Sb show clear hysteresis, demonstrating the presence of ferromagnetic order. The Curie temperature (TC) increases with increasing x and reaches 140 K at x = 13.7%. The crystal structure analyses, magneto-transport, and magneto-optical properties indicate that (Ga,Fe)Sb is an intrinsic ferromagnetic semiconductor.

Electrical control of ferromagnetism in the n-type ferromagnetic semiconductor (In,Fe)Sb with high Curie temperature

By studying the electrical control of the magnetic properties of ferromagnetic semiconductors (FMSs), we can understand many fundamental aspects of carrier-induced ferromagnetism and explore the possibilities of device applications. Previous experiments on the electrical control of ferromagnetism in Mn-doped FMSs were limited to very low temperatures due to their low Curie temperature (TC). Here, we demonstrate electrical control ferromagnetism at high temperature (210 K) in an electric double layer transistor with an n-type high-TC FMS (In0.89,Fe0.11)Sb thin film channel. A liquid electrolyte is used instead of a conventional solid gate to obtain a large change (40%) of the electron density in the (In0.89,Fe0.11)Sb channel. By applying a small gate voltage (0 → +5 V), TC of the (In,Fe)Sb thin film can be changed by 7 K, indicating that the magnetization as well as ferromagnetic phase transition in (In,Fe)Sb can be controlled at high temperature by the gate electric field despite a small change of electron concentration Δn = 2.2 × 1017 cm−3. Our result paves a way for realizing semiconductor spintronic devices operating at room temperature with low power consumption.By studying the electrical control of the magnetic properties of ferromagnetic semiconductors (FMSs), we can understand many fundamental aspects of carrier-induced ferromagnetism and explore the possibilities of device applications. Previous experiments on the electrical control of ferromagnetism in Mn-doped FMSs were limited to very low temperatures due to their low Curie temperature (TC). Here, we demonstrate electrical control ferromagnetism at high temperature (210 K) in an electric double layer transistor with an n-type high-TC FMS (In0.89,Fe0.11)Sb thin film channel. A liquid electrolyte is used instead of a conventional solid gate to obtain a large change (40%) of the electron density in the (In0.89,Fe0.11)Sb channel. By applying a small gate voltage (0 → +5 V), TC of the (In,Fe)Sb thin film can be changed by 7 K, indicating that the magnetization as well as ferromagnetic phase transition in (In,Fe)Sb can be controlled at high temperature by the gate electric field despite a small change of electro...

Epitaxial growth and characterization of n-type magnetic semiconductor (In,Co)As

A new n-type magnetic semiconductor (In1−x,Cox)As (x = 3–18%) has been successfully grown by low-temperature molecular beam epitaxy (LT-MBE) on GaAs(001) substrates. Reflection high energy electron diffraction (RHEED) patterns during the MBE growth and transmission electron microscopy (TEM) images indicate that (In,Co)As layers have zinc-blende crystal structure with a small fraction of embedded CoAs nanoclusters. The electron concentration of the (In,Co)As layers can be changed in the range of 1.9 × 1018–2.4 × 1019 cm−3 by changing the Co concentration. The metal–insulator transition (MIT) is observed at x = 5%. Large negative magnetoresistance (up to −17.5% at 0.95 T) is observed at low temperature and can be attributed to spin-disorder scattering in the (In,Co)As matrix.

Planar Nernst effect and Mott relation in (In,Fe)Sb ferromagnetic semiconductor

Transverse magneto-thermoelectric effects were studied in an (In,Fe)Sb ferromagnetic semiconductor thin film under an in-plane magnetic field. We find that the thermal voltage is governed by the planar Nernst effect. We show that the magnetic field intensity dependence, magnetic field direction dependence, and temperature dependence of the transverse Seebeck coefficient can be explained by assuming a Mott relation between the in-plane magneto-transport and magneto-thermoelectric phenomena in (In,Fe)Sb.