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Register a new userControl of ferromagnetism by manipulating the carrier wavefunction in ferromagnetic semiconductor (In,Fe)As quantum wells
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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.
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We demonstrate electrical control of ferromagnetism in field-effect transistors with a trilayer quantum well (QW) channel containing an ultrathin n-type ferromagnetic semiconductor (In,Fe)As layer. A gate voltage is applied to control the electron wavefunctions {phi}i in the QW, such that the overlap of {phi}i and the (In,Fe)As layer is modified. The Curie temperature is largely changed by 42%, whereas the change in sheet carrier concentration is 2 - 3 orders of magnitude smaller than that of previous gating experiments. This result provides a new approach for versatile, low power, and ultrafast manipulation of magnetization.
The electronic and magnetic properties of Fe atoms in the ferromagnetic semiconductor (In,Fe)As codoped with Be have been studied by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe $L_{2,3}$ edge. The XAS and XMCD spectra showed simple spectral line shapes similar to Fe metal, but the ratio of the orbital and spin magnetic moments ($M_mathrm{orb}$/$M_mathrm{spin}$) estimated using the XMCD sum rules was significantly larger than that of Fe metal, indicating a significant orbital moment of Fe $3d$ electrons in (In,Fe)As:Be. The positive value of $M_mathrm{orb}$/$M_mathrm{spin}$ implies that the Fe $3d$ shell is more than half-filled, which arises from the hybridization of the Fe$^{3+}$ ($d^5$) state with the charge-transfer $d^6underline{L}$ states, where $underline{L}$ is a ligand hole in the host valence band. The XMCD intensity as a function of magnetic field indicated hysteretic behavior of the superparamagnetic-like component due to discrete ferromagnetic domains.
We report single-color, time resolved magneto-optical measurements in ferromagnetic semiconductor (Ga,Mn)As. We demonstrate coherent optical control of the magnetization precession by applying two successive ultrashort laser pulses. The magnetic field and temperature dependent experiments reveal the collective Mn-moment nature of the oscillatory part of the time-dependent Kerr rotation, as well as contributions to the magneto-optical signal that are not connected with the magnetization dynamics.
Spatially indirect Type-II band alignment in magnetically-doped quantum dot (QD) structures provides unexplored opportunities to control the magnetic interaction between carrier wavefunction in the QD and magnetic impurities. Unlike the extensively studied, spatially direct, QDs with Type-I band alignment where both electrons and holes are confined in the QD, in ZnTe QDs embedded in a (Zn,Mn)Se matrix only the holes are confined in the QDs. Photoexcitation with photon energy 3.06 eV (2.54 eV) generates electron-hole pairs predominantly in the (Zn,Mn)Se matrix (ZnTe QDs). The photoluminescence (PL) at 7 K in the presence of an external magnetic field exhibits an up to three-fold increase in the saturation red shift with the 2.54 eV excitation compared to the shift observed with 3.06 eV excitation. This unexpected result is attributed to multiple hole occupancy of the QD and the resulting increased penetration of the hole wavefunction tail further into the (Zn,Mn)Se matrix. The proposed model is supported by microscopic calculations which accurately include the role of hole-hole Coulomb interactions as well as the hole-Mn spin exchange interactions.
The (In,Fe)Sb layers with the Fe content up to 13 at. % have been grown on (001) GaAs substrates using the pulsed laser deposition. The TEM investigations show that the (In,Fe)Sb layers are epitaxial and free of the inclusions of a second phase. The observation of the hysteretic magnetoresistance curves at temperatures up to 300 K reveals that the Curie point is above room temperature. The resonant character of magnetic circular dichroism confirms the intrinsic ferromagnetism in the (In,Fe)Sb layers. We suggest that the ferromagnetism of the (In,Fe)Sb matrix is not carrier-mediated and apparently is determined by the mechanism of superexchange interaction between Fe atoms (This work was presented at the XXI Symposium Nanophysics and Nanoelectronics, Nizhny Novgorod, March, 13-16, 2017 (book of proceedings v.1, p. 195), http://nanosymp.ru/UserFiles/Symp/2017_v1.pdf).
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