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Register a new userHeavily Fe-doped n-type ferromagnetic semiconductor (In,Fe)Sb with high Curie temperature and large magnetic anisotropy
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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.
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(Ga$_{1-x}$,Fe$_x$)Sb is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature ($T_{rm C}$) is above 300 K when the Fe concentration $x$ is equal to or higher than ~0.20. However, the origin of the high $T_{rm C}$ in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the $x$ dependence of the Fe 3$d$ states in (Ga$_{1-x}$,Fe$_x$)Sb ($x$ = 0.05, 0.15, and 0.25) thin films. The observed Fe 2$p$-3$d$ RPES spectra reveal that the Fe-3$d$ impurity band (IB) crossing the Fermi level becomes broader with increasing $x$, which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3$d$ partial density of states and the first-principles calculations suggests that the Fe-3$d$ IB originates from the minority-spin ($downarrow$) $e$ states. The results indicate that enhancement of the interaction between $e_downarrow$ electrons with increasing $x$ is the origin of the high $T_{rm C}$ in (Ga,Fe)Sb.
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.
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).
Room temperature ferromagnetism was observed in n-type Fe-doped In2O3 thin films deposited on c-cut sapphire substrates by pulsed laser deposition. Structure, magnetism, composition, and transport studies indicated that Fe occupied the In sites of the In2O3 lattice rather than formed any metallic Fe or other magnetic impurity phases. Magnetic moments of films were proved to be intrinsic and showed to have a strong dependence on the carrier densities which depended on the Fe concentration and its valance state as well as oxygen pressure.
We show that by introducing isoelectronic iron (Fe) magnetic impurities and Beryllium (Be) double-donor atoms into InAs, it is possible to grow a n-type ferromagnetic semiconductor (FMS) with the ability to control ferromagnetism by both Fe and independent carrier doping by low-temperature molecular-beam epitaxy. We demonstrate that (In,Fe)As doped with electrons behaves as an n-type electron-induced FMS. This achievement opens the way to realize novel spin-devices such as spin light-emitting diodes or spin field-effect transistors, as well as helps understand the mechanism of carrier-mediated ferromagnetism in FMSs.
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