J. Panda

Electrical spin extraction and giant positive junction magnetoresistance in a Fe3O4/MgO/n-Si magnetic diode like heterostructure

We have demonstrated here the electrical spin extraction and origin of giant positive junction magnetoresistance (JMR) in our Fe3O4/MgO/n-Si (0 0 1) heterostucture. The heterostructure has been fabricated using pulsed laser deposition technique. The electrical transport properties of this heterostructure have been investigated in the temperature range 10–300 K. The current–voltage characteristics of the heterojunction with and without an applied 6 T magnetic field shows very good rectifying magnetic diode like behaviour throughout the temperature range. The magnetic field dependent JMR behaviour of our heterostucture has been measured in the same temperature range. The heterostructure shows a giant positive JMR at 10 K (~2279%) that gradually decreases at higher temperatures. The temperature dependent spin polarization, spin diffusion length and spin life time have been estimated for our heterostructure showing a maximum at 60 K (~0.77, 470 nm and 127 ps, respectively). The origin of the JMR has been best explained by standard spin injection/extraction and spin accumulation theory in n-Si. The JMR value for our heterostructure saturates at a much lower external magnetic field as compared to reported other heterostructures, thus making it a better choice for magnetic diodes in spintronics.

Magnetic and optical properties of Mn-doped ZnO vertically aligned nanorods synthesized by hydrothermal technique

In this paper we have reported the synthesis of high quality vertically aligned undoped and Mn-doped ZnO single crystalline nanorods arrays on Si (100) substrates using two steps process, namely, initial slow seed layer formation followed by solution growth employing wet chemical hydrothermal method. The shapes of the as grown single crystalline nanorods are hexagonal. The diameter and length of the as grown undoped ZnO nanorods varies in the range of 80-150 nm and 1.0 - 1.4 μm, respectively. Along with the lattice parameters of the hexagonal crystal structure, the diameter and length of Mn doped ZnO nanorods are found to increase slightly as compared to the undoped ZnO nanorods. The X-ray photoelectron spectroscopy confirms the presence of Mn atoms in Mn2+ state in the single crystalline ZnO nanorods. The recorded photoluminescence spectrum contains two emissions peaks having UV exciton emissions along with a green-yellow emission. The green-yellow emissions provide the evidence of singly ionized oxygen ...

Structural and magnetization behavior of highly spin polarized Co2CrAl full Heusler alloy

The half metallic ferromagnet Co2CrAl full Huesler alloy was successfully prepared by arc melting process. The electrical and magnetic properties of Co2CrAl alloy have been studied in the temperature range of 5 – 300 K. The ferromagnetic Curie temperature Tc of the same alloy has been observed at 329.8 K. The alloy shows semiconducting like electronic transport behavior throughout the studied temperature range. The origin of the semiconducting behavior of Co2CrAl alloy can be best explained by the localization of conduction electrons and the presence of an energy gap in the electronic spectrum near the Fermi level EF.

Enhanced temperature dependent junction magnetoresistance in La0.7Sr0.3MnO3/Zn(Fe, Al)O carrier induced dilute magnetic semiconductor junctions

Metal-semiconductor type junction based on p-type La0.7Sr0.3MnO3 and n-type ZnO, Zn(Fe)O or Zn(Fe,Al)O with different Fe concentrations have been fabricated on (0001) sapphire substrate using pulsed laser deposition technique. While the metal-semiconductor type junction with La0.7Sr0.3MnO3 (LSMO) and ZnO or Zn(Fe)O show very good rectifying behavior, the heterojunction with La0.7Sr0.3MnO3 and Zn(Fe,Al)O fails to show such rectifying characteristics which most likely due to the much higher carrier concentration and thin depletion width. These metal-semiconductor type junctions show reasonably high temperature dependent junction magnetoresistive behavior. At 77 and 300 K all the junctions show negative junction magnetoresistance, whereas they show positive junction magnetoresistance at certain temperature range (150–280 K). The junction MR attains a peak with high positive value ∼76%, 38%, and 25% for LSMO/Zn(Fe,Al)O, LSMO/Zn(Fe)O, and LSMO/ZnO junctions, respectively, near 250 K, where La0.7Sr0.3MnO3 shows...

Investigation of junction magnetoresistance in Co0.65Zn0.35Fe2O4/p-Si heterostructure for spintronics

The zinc doped cobalt ferrite (Co0.65Zn0.35Fe2O4) thin film has been fabricated on p-Si substrate (100) using pulsed laser deposition technique. The Current-Voltage characteristics without and with external 6 T magnetic field have been measured at different temperatures in the range of 5-300 K across the junction (CZFO/p-Si). The junction shows good rectifying behavior throughout the temperature range. The magnetic field dependent junction magnetoresistance (JMR) behavior of the heterojunction (CZFO/p-Si) have been studied at a constant temperature. The heterojunction shows positive JMR throughout the temperature range. The highest positive JMR observed at low temperature 5 K and decreases at higher temperatures.

Electrical spin injection from CoFe2O4 into p-Si semiconductor across MgO tunnel barrier for spin electronics

The room temperature spin injection and detection in non magnetic p-Si semiconductor have been studied in details in our CoFe2O4 (CFO)/MgO/p-Si heterojunction. The 3-terminal tunnel contacts have been made on the device for transport measurements. The electrical transport properties have been investigated at different isothermal conditions in the temperature range of 10-300 K. The spin accumulation in non magnetic p-Si semiconductor has been observed at different bias current under the applied magnetic field parallel to the film plane in the temperature range of 40-300 K. We have observed a giant spin accumulation in p-Si semiconductor using MgO/CFO tunnel contact. The Hanley effect is used to control the reduction of spin accumulation by applying magnetic field perpendicular to the carrier spin in the p-Si. The accumulated spin signal decays as a function of applied magnetic field for fixed bias current. These results will enable utilization of the spin degree of freedom in complementary Si devices and i...

Electronic and magneto transport property of Pr0.7Sr0.3MnO3 system in nanometric gran size modulation

Grain size effect on electronic- and magnto-transport properties of hole doped manganite Pr0.7Sr0.3MnO3 (PSMO) in nanometric dimension has been thoroughly investigated under external magnetic field range from zero to ± 8 Tesla down to 4 K. Metal-insulator transition temperature (Tp) which is observed for all the PSMO nanometric samples, differs from the ferromagnetic to paramagnetic transition temperature (Tc) in the nanometric regime compare to its reported bulk counterpart mainly due to the enhanced surface disorder effect. Temperature dependent low field complex magneto- impedance (LFMI) behaviour has also been studied in presence of external magnetic field range of 0 – 800 Oe down to 77 K.

Electrical and Magneto-electronic Properties of p-La0.7Ca0.3MnO3/ SrTiO3/n-Si Heterostructure for Spintronics Application

An experimental study of p-La0.7Ca0.3MnO3/ SrTiO3/n-Si heterostructure in which the LCMO and Si are separated by a thin interfacial SrTiO3 (STO) layer with typical thickness of about 15 nm, has been in situ fabricated with the Pulsed laser deposition technique. The La0.7Ca0.3MnO3 (LCMO) film of about 70 nm has been grown on STO at substrate (n-Si) temperature of 800°C in 0.5 mbar oxygen pressure. The junction exhibits good rectifying behavior over the temperature range of 10 – 300 K. Electrical properties of p-La0.7Ca0.3MnO3/STO/n-Si MOS like heterostructure exhibits nonlinear I-V characteristics in a wide temperature range. The heterostructure also exhibits MOS-diode like behavior with all type of possible current flow mechanisms (such as thermionic emission, tunneling, recombination, degeneration, etc.) through the heterojunction. The ideality factor, reverse saturation current, series resistances and turn-on voltages of the heterojunction have been estimated at different operating temperatures. The junction magnetoresistance (JMR) properties of p-LCMO/STO/n-Si heterostructure have been studied over the temperature range of 100-300 K. The current-voltage characteristics at all temperatures conclusively show the high sensitivity junction magnetoresistance (JMR – 48% at 150 K and ~ 30% at 300 K) under the external 7 T magnetic field. The JMR is positive and strongly depends on temperature at an applied forward bias voltage (3 V). The relation between JMR and external magnetic field is found to be of (Δρ/ρ ≈ α Hβ) type having both α and β temperature dependent. We attribute the emergence of positive JMR to the quantum mechanical tunneling transport mechanism along with the modification of barrier height across the heterojunction.

Electronic transport, ac-susceptibility, and magnetotransport studies of Pr0.6Sr0.4MnO3 manganite nanoparticles

We investigated the electronic transport, magnetic, and magneto-transport properties of perovskite Pr0.6Sr0.4MnO3 (PSMO) manganite in nanometric grain size modulations in the range of 32-50 nm. Structural property confirms all samples are in single phase well crystallined with Pbnm space group. In the electronic transport nanometric sample shows a metal-insulator transition varying from 215 K to 275 K. The low field magnetoresistance (LFMR) (upto 1 Tesla) of the lowest nanometric sample is found maximum (∼55%) at 10 K compared to other nanometric samples. However, in nanometric dimension, paramagnetic to ferromagnetic transition temperatures are increased rather than its reported bulk counterpart value (∼300 K). The micro-structural, ac-susceptibility, electronic-, magneto-transport properties in nano manganites is analyzed on the basis of enhanced surface disorder at the grain surface in order to explain the appearance of metallicity, LFMR and modified magnetic properties.

Temperature dependent spin injection properties of self-assembled epitaxial Ni nanoparticles embedded metallic TiN matrix/p-Si heterojunction

The epitaxial Ni nanoparticles embedded in metallic TiN matrix [TiN(Ni)] on p-type (001) Si heterojunction [TiN(Ni)/(001)p-Si] has been fabricated using pulsed laser deposition technique. The I-V characteriatics of TiN(Ni)/p-Si heterojunction have been studied at different temperatures in the range of 100-300 K. The heterojunction shows reasonably good diode like rectifying behavior in this temperature range. The ideality factor, reverse saturation current, series resistance and turn-on voltages have been estimated at different operating temperatures. The magnetoresistance (MR) properties of TiN(Ni) film and the junction MR of TiN(Ni)/p-Si heterojunction have been studied up to a magnetic field of 8 Tesla. The junction MR attains a peak with high positive junction MR value at 250 K. The origin of high value of junction MR has been best explained using standard spin injection theory.