Origin of the Early Mesozoic Granitic Rocks in the Hida Terrane, Japan, and Its Implication for Evolution of the Continental Crust

The early Mesozoic granitic rocks show Rb-Sr ages of 173 to 211 Ma and are intruded into three belts, Hida Gneiss Belt, Unazuki Belt and Hida Marginal Belt, being divided into Triassic ones and Jurassic ones. The granitic rocks exhibit spatial variation in chemical compositions of constituent minerals, whole-rock geochemistry and Sr and Nd isotopic data. Especially, based on Sr and Nd isotopic compositions of the granites, the Hida Terrane (Hida Gneiss Belt and Unazuki Belt) can be divided roughly into two zones, Outer Plutonic Zone (lower initial 87Sr86Sr ratios: 0.7045 to 0.7065 and higher initial εNd values: +3.1 to -4.2) and Inner Plutonic Zone (higher initial 87Sr/86Sr ratios: 0.7054 to 0.7105 and lower initial εNd values: +1.6 to -9.3). Gabbroic rocks indicate the same spatial variation in isotopic characteristics of the granitic rocks. The negative initial εNd values (-3.3 and -4.2) from Triassic Hayatsukigawa mass suggest that its formation was incorporated by significant amounts of older continental crust. The mass is characterized by low K2O/Na2O ratios, Rb and MgO contents and high Sr and Ba contents. The granites belong to the I-type and magnetite-series granitic rocks, which is the same in the Jurassic granitic rocks. The geochemical data indicate that the magma source of the Hayatsukigawa mass rocks is a granulite facies igneous lower crust. The main partial melting in the lower crust may be induced by adiabatic decompression resulting from the rapid uplifting occurred in the Outer Plutonic Zone. The geochemical criteria imply that the Jurassic granites was generated in a destructive plate margin. From the isotopic data and geochemical characteristics, the granitic rocks in the Outer Plutonic Zone may have been derived from Phanerozoic basic igneous rocks (e.g. basaltic composition) with island-arc or continental margin character. The granitic rocks in the Inner Plutonic Zone can be divided into two groups, Group I and Group II on the basis of their isotopic compositions. The source material of the Group Ⅰ is inferred to have been enriched in 87Sr than that of the granites in the Outer Plutonic Zone. The Group II rocks with higher initial 87Sr/86Sr ratios and lower εNd values appear to have primarily been derived from older (Proterozoic) crustal sources. Considering the isotopic and geochemical informations of the early Mesozoic granitic rocks and Hida metamorphic rocks, the Inner Plutoni Zone of the Hida Terrane would have been an island arc or a microcontinent which collided with the eastern edge of the Sino-Korean craton during the early Paleozoic

Artificial control of the bias-voltage dependence of tunnelling anisotropic magnetoresistance using quantization in a single-crystal ferromagnet

A major issue in the development of spintronic memory devices is the reduction of the power consumption for the magnetization reversal. For this purpose, the artificial control of the magnetic anisotropy of ferromagnetic materials is of great importance. Here, we demonstrate the control of the carrier-energy dependence of the magnetic anisotropy of the density of states (DOS) using the quantum size effect in a single-crystal ferromagnetic material, GaMnAs. We show that the mainly two-fold symmetry of the magnetic anisotropy of DOS, which is attributed to the impurity band, is changed to a four-fold symmetry by enhancing the quantum size effect in the valence band of the GaMnAs quantum wells. By combination with the gate-electric field control technique, our concept of the usage of the quantum size effect for the control of the magnetism will pave the way for the ultra-low-power manipulation of magnetization in future spintronic devices.Comment: 9 pages, 7 figure

Anomalous Fermi level behavior in GaMnAs at the onset of ferromagnetism

We present the systematic study of the resonant tunneling spectroscopy on a series of ferromagnetic-semiconductor Ga1-xMnxAs with the Mn content x from ~0.01 to 3.2%. The Fermi level of Ga1-xMnxAs exists in the band gap in the whole x region. The Fermi level is closest to the valence band (VB) at x=1.0% corresponding to the onset of ferromagnetism near the metal-insulator transition (MIT), but it moves away from the VB as x increasing or decreasing from 1.0%. This anomalous behavior of the Fermi level indicates that the ferromagnetism and MIT emerge in the Mn-derived impurity band.Comment: 4 pages, 4 figures, 1 table (minor revision

Properties and Curie Temperature (130 K) of Heavily Mn-doped Quaternary Alloy Ferromagnetic Semiconductor (InGaMn)As Grown on InP

We have studied magnetic properties of heavily Mn-doped [(In0.44Ga0.56)0.79Mn0.21]As thin films grown by low-temperature molecular-beam epitaxy (LT-MBE) on InP substrates. The (InGaMn)As with high Mn content (21%) was obtained by decreasing the growth temperature to 190 degC. When the thickness of the [(In0.44Ga0.56)0.79Mn0.21]As layer is equal or thinner than 10 nm, the reflection high-energy electron diffraction (RHEED) pattern and transmission electron microscopy (TEM) show no MnAs clustering, indicating that a homogeneous single crystal with good quality was grown. In the magnetic circular dicroism (MCD) measurement, large MCD intensity and high Curie temperature of 130 K were observed.Comment: 3 pages, 5 figure

Valence-band structure of ferromagnetic semiconductor (InGaMn)As

To clarify the whole picture of the valence-band structures of prototype ferromagnetic semiconductors (III,Mn)As (III: In and Ga), we perform systematic experiments of the resonant tunneling spectroscopy on [(In_0.53Ga_0.47)_1-x Mn_x]As (x=0.06-0.15) and In_0.87Mn_0.13As grown on AlAs/ In_0.53Ga_0.47As:Be/ p+InP(001). We show that the valence band of InGaMnAs almost remains unchanged from that of the host semiconductor InGaAs, that the Fermi level exists in the band gap, and that the p-d exchange splitting in the valence band is negligibly small in (InGaMn)As. In the In0.87Mn0.13As sample, although the resonant peaks are very weak due to the large strain induced by the lattice mismatch between InP and InMnAs, our results also indicate that the Fermi level exists in the band gap and that the p-d exchange splitting in the valence band is negligibly small. These results are quite similar to those of GaMnAs obtained by the same method, meaning that there are no holes in the valence band, and that the impurity-band holes dominate the transport and magnetism both in the InGaMnAs and In_0.87Mn_0.13As films. This band picture of (III,Mn)As is remarkably different from that of II-VI-based diluted magnetic semiconductors.Comment: 21 pages, 6 figures, accepted for publication in Phys. Rev.