Ferromagnetic semiconductors (FMS), which inherit properties of both semiconductors
and ferromagnetic materials, are realized by doping a certain amount (several %) of magnetic
elements in semiconductors. In the past, most of the research has been dedicated to Mn-doped
III-V FMSs, which are only P-type and the highest Curie temperature (T C ) is 200 K. Recently,
we presented an alternative approach by using Fe instead of Mn as the magnetic dopants in
narrow-gap III-V semiconductors like InAs, GaSb, and InSb. Using low-temperature
molecular beam epitaxy (MBE), we have successfully grown both P-type FMS [(Ga,Fe)Sb] [1] and N-type FMSs [(In,Fe)As [2,3], (In,Fe)Sb [4]]. Intrinsic room-temperature
ferromagnetism has been observed in (Ga 1-x ,Fe x )Sb with x > 23% [1] and (In 1-x ,Fe x )Sb with x >
16% [4].
In this talk, we present new novel magnetotransport physics in bilayer structures of a
nonmagnetic (NM) material and an Fe-doped FMS, where a magnetic proximity effect (MPE)
from the FMS is expected to affect the NM channel. The sample structure consists of InAs
(thickness t = 15 – 40 nm)/(Ga,Fe)Sb (15 nm, 20% Fe) grown on AlSb buffer/semi-insulating
GaAs (100) substrates (Fig. 2a,b). We found that a strong and long-range MPE is induced at
the InAs/(Ga,Fe)Sb interface, resulting in a spontaneous spin splitting ΔE, as large as 18 meV,
in the InAs channel[5,6]. Furthermore, this spin splitting ΔE can be largely modulated by
applying a gate voltage V g . We observed a giant even-parity magnetoresistance (~80% at 14
T), which we call proximity magnetoresistance (PMR) [5,6], and a large odd-parity linear
magnetoresistance (OMR) [7], corresponding to a resistance change of 27% when the
perpendicular-to-plane magnetic field B (=10 T) direction is reversed. The unprecedented
large OMR was found to occur in the edge transport channels of the InAs thin film, due to
simultaneous breaking of both the space inversion symmetry (SIS) and the time reversal
symmetry (TRS) (Fig. 1a). These new features realized in the Fe-doped FMSs and their
quantum heterostructures are particularly important for the applications of low-power and
high-speed spin-based electronics. Furthermore, the gate-controllable spin splitting provides a
mechanism to locally access Majorana fermions in InAs-based Josephson junctions [8].
These works were partly supported by Grants-in-Aid for Scientific Research, the
CREST and PRESTO Programs of JST, the UTEC-UTokyo FSI program, Murata Science
Foundation and Spin-RNJ.

References
[1] N. T. Tu et al., Appl. Phys. Lett. 108, 192401 (2016).　
[2] P. N. Hai, L. D. Anh et al., Appl. Phys. Lett. 101, 252410 (2012).　
[3] L. D. Anh et al., Nat. Commun. 7, 13810 (2016).
[4] N. T. Tu, P. N. Hai, L. D. Anh, M. Tanaka, APEX 11 (6), 063005 (2018).　
[5] H. Shiratani et al., Comm. Phys. (2024, in press).　
[6] K. Takiguchi, L. D. Anh et al., Nature Phys. 15, 1134 (2019).
[7] K. Takiguchi, L. D. Anh et al., Nature Commun. 13, 6538 (2022).
[8] J. Alicea, Rep. Prog. Phys. 75, 076501 (2012).