399 research outputs found
Recent Progress in III-V based ferromagnetic semiconductors: Band structure, Fermi level, and tunneling transport
Spin-based electronics or spintronics is an emerging field, in which we try
to utilize spin degrees of freedom as well as charge transport in materials and
devices. While metal-based spin-devices, such as magnetic-field sensors and
magnetoresistive random access memory using giant magnetoresistance and
tunneling magnetoresistance, are already put to practical use,
semiconductor-based spintronics has greater potential for expansion because of
good compatibility with existing semiconductor technology. Many
semiconductor-based spintronics devices with useful functionalities have been
proposed and explored so far. To realize those devices and functionalities, we
definitely need appropriate materials which have both the properties of
semiconductors and ferromagnets. Ferromagnetic semiconductors (FMS), which are
alloy semiconductors containing magnetic atoms such as Mn and Fe, are one of
the most promising classes of materials for this purpose, and thus have been
intensively studied for the past two decades. Here, we review the recent
progress in the studies of the most prototypical III-V based FMS, p-type
(GaMn)As, and its heterostructures with focus on tunneling transport, Fermi
level, and bandstructure. Furthermore, we cover the properties of a new n-type
FMS, (InFe)As, which shows electron-induced ferromagnetism. These FMS materials
having zinc-blende crystal structure show excellent compatibility with
well-developed III-V heterostructures and devices.Comment: Accepted in Applied Physics Review
Control of ferromagnetism by manipulating the carrier wavefunction in ferromagnetic semiconductor (In,Fe)As quantum wells
We demonstrated the control of ferromagnetism in a surface quantum well
containing a 5-nm-thick n-type ferromagnetic semiconductor (In,Fe)As layer
sandwiched between two InAs layers, by manipulating the carrier wavefunction.
The Curie temperature (Tc) of the (In,Fe)As layer was effectively changed by up
to 12 K ({\Delta}Tc/Tc = 55%). Our calculation using the mean-field Zener
theory reveals an unexpectedly large s-d exchange interaction in (In,Fe)As. Our
results establish an effective way to control the ferromagnetism in quantum
heterostructures of n-type FMSs, as well as require reconsideration on the
current understanding of the s-d exchange interaction in narrow gap FMSs.Comment: 28 pages icluding both main text(15 pages, 4 figures) and
supplementary information (13 pages
Origin of the giant spin Hall effect in BiSb topological insulator
The giant spin Hall effect (SHE) at room temperature is one of the most
attractive feature of topological insulators (TIs) for applications to
nano-scale spin devices. Its origin, however, remains a controversial problem.
Here, we identify the origin of the giant SHE in BiSb thin films by measuring
the spin Hall angle under controllable contribution of surface
and bulk conduction. We found that of a BiSb TI
thin film takes colossal values (450 - 530 at 8 K, and 38 at 300 K), and is
almost governed by contribution from the topological surface states. Meanwhile,
in a BiSb semi-metallic thin film without
topological surface states drastically decreases. Our results provide a
quantitative tool for analysing the origin of the giant SHE in TI thin films,
as well as a strategy for designing spin current source utilizing the surface
states of TI in high-performance nano-scale spin devices
Spin-dependent transport properties in GaMnAs-based spin hot-carrier transistors
We have investigated the spin-dependent transport properties of GaMnAs-based
three-terminal semiconductor spin hot-carrier transistor (SSHCT) structures.
The emitter-base bias voltage VEB dependence of the collector current IC,
emitter current IE, and base current IB shows that the current transfer ratio
alpha (= IC / IE) and the current gain beta (= IC / IB) are 0.8-0.95 and 1-10,
respectively, which means that GaMnAs-based SSHCTs have current amplifiability.
In addition, we observed an oscillatory behavior of the tunneling
magnetoresistance (TMR) ratio with the increasing bias, which can be explained
by the resonant tunneling effect in the GaMnAs quantum well.Comment: 10 pages, 4 figures, submitted to AP
Second main theorems with weighted counting functions and its applications
The purpose of this article has two fold. The first is to generalize some
recent second main theorems for the mappings and moving hyperplanes of
\P^n(\C) to the case where the counting functions are truncated multiplicity
(by level ) and have different weights. As its application, the second
purpose of this article is to generalize and improve some algebraic dependence
theorems for meromorphic mappings having the same inverse images of some moving
hyperplanes to the case where the moving hyperplanes involve the assumption
with different roles.Comment: This article has been accepted for publication in the Indian Journal
of Pure and Applied Mathematics since August 201
Bias-field-free spin Hall nano-oscillators with an out-of-plane precession mode
Spin Hall nano-oscillators (SHNOs) are promising candidates for new microwave
oscillators with high durability due to a small driving current. However,
conventional SHNOs with an in-plane precession (IPP) mode require a bias field
for stable oscillations which is not favored in certain applications such as
neuromorphic computing. Here, we propose and theoretically analyze a
bias-field-free SHNO with an in-plane hard axis and an out-of-plane precession
(OPP) mode by solving the Landau-Lifshitz-Gilbert (LLG) equation analytically
and numerically. We derive formulas for driving currents and precession
frequency, and show that they are in good agreement with numerical simulation
results. We show that our proposed SHNOs can be driven by much smaller bias
current than conventional spin torque nano-oscillators
Comment on "Reconciling results of tunnelling experiments on (Ga,Mn)As" arXiv:1102.3267v2 by Dietl and Sztenkiel
We comment on the recent paper "Reconciling results of tunnelling experiments
on (Ga,Mn)As" arXiv:1102.3267v2 by Dietl and Sztenkiel. They claimed that the
oscillations observed in the d2I/dV2-V characteristics in our studies on the
resonant tunneling spectroscopy on GaMnAs, are not attributed to the resonant
levels in the GaMnAs layer but to the two-dimensional interfacial subbands in
the GaAs:Be layer. Here, we show that this interpretation is not able to
explain our experimental results and our conclusions remain unchanged.Comment: 5 pages, 2 figure
Heavily Fe-doped n-type ferromagnetic semiconductor (In,Fe)Sb with high Curie temperature and large magnetic anisotropy
We present high-temperature ferromagnetism and large magnetic anisotropy in
heavily Fe-doped n-type ferromagnetic semiconductor (In1-x,Fex)Sb (x = 20 -
35%) thin films grown by low-temperature molecular beam epitaxy. The
(In1-x,Fex)Sb thin films with x = 20 - 35% maintain the zinc-blende crystal and
band structure with single-phase ferromagnetism. The Curie temperature (TC) of
(In1-x,Fex)Sb reaches 390 K at x = 35%, which is significantly higher than room
temperature and the highest value so far reported in III-V based ferromagnetic
semiconductors. Moreover, large coercive force (HC = 160 Oe) and large remanent
magnetization (Mr/MS = 71%) have been observed for a (In1-x,Fex)Sb thin film
with x = 35%. Our results indicate that the n-type ferromagnetic semiconductor
(In1-x,Fex)Sb is very promising for spintronics devices operating at room
temperature.Comment: arXiv admin note: text overlap with arXiv:1706.0073
Giant unidirectional magnetoresistance in topological insulator -- ferromagnetic semiconductor heterostructures
The unidirectional magnetoresistance (UMR) is one of the most complex
spin-dependent transport phenomena in ferromagnet/non-magnet bilayers, which
involves spin injection and accumulation due to the spin Hall effect (SHE) or
Rashba-Edelstein effect (REE), spin-dependent scattering, and magnon scattering
at the interface or in the bulk of the ferromagnet. While UMR in metallic
bilayers has been studied extensively in very recent years, its magnitude is as
small as 10, which is too small for practical applications. Here, we
demonstrate a giant UMR effect in a heterostructure of BiSb topological
insulator -- GaMnAs ferromagnetic semiconductor. We obtained a large UMR ratio
of 1.1%, and found that this giant UMR is governed not by the giant
magnetoresistance (GMR)-like spin-dependent scattering, but by magnon
emission/absorption and strong spin-disorder scattering in the GaMnAs layer.
Our results provide new insight into the complex physics of UMR, as well as a
strategy for enhancing its magnitude for device applications
Spin-orbit torque as a method for field-free detection of in-plane magnetization switching
We proposed and demonstrated a simple method for detection of in-plane
magnetization switching by spin-orbit torque (SOT) in bilayers of non-magnetic
/ magnetic materials. In our method, SOT is used not only for magnetization
switching but also for detection. Our method can detect arbitrary Mx and My
component without an external magnetic field, which is useful for fast
characterization of type-X, type-Y, and type-XY SOT magnetization switching.
Our SOT detection scheme can be utilized not only for fast characterization of
SOT switching in bilayers, but also for electrical detection of in-plane
magnetic domains in race-track memory
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