Positive Junction Magnetoresistance Research Articles

Enhanced Spin Accumulation in Semiconductor at Room Temperature Using Ni0.65Zn0.35Fe2O4(NZFO) as Spin Injector in NZFO/MgO/p-Si Device

In this article, the fabrication of a Ni0.65Zn0.35Fe2O4/MgO/p-Si heterostructure device has been optimized using the pulsed laser deposition (PLD) technique, and a detailed investigation of its structural, electrical, and magnetic features has been performed experimentally. The electronic and magneto-transport characteristics have been explored in the temperature range of 100–300 K. The current-voltage (I-V) characteristics of the heterojunction have been recorded, which displayed an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The application of an external magnetic field parallel to the plane of the NZFO film causes the current (I) across the junction to decrease, clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. The root of displaying positive magnetoresistance in our heterojunction has been well justified using the standard spin injection model. The electrical injection of spin-polarized carriers and its accumulation and detection in a p-Si channel have been demonstrated using the NZFO/MgO tunnel contact using a three-terminal (3-T) Hanle device. The parameters such as spin lifetime (99 ps), spin diffusion length (276 nm), and spin polarization (0.44) have been estimated from the Hanle curve detected in our heterostructure at room temperature, making the Ni0.65Zn0.35Fe2O4/MgO/p-Si device a very favorable promising junction structure in the field of spintronics for several device appliances in the future.

Spin valve-like magnetic tunnel diode exhibiting giant positive junction magnetoresistance at low temperature in Co2MnSi/SiO2/p-Si heterostructure

The rectifying magnetic tunnel diode has been fabricated by growing Co2MnSi (CMS) Heusler alloy film carefully on a properly cleaned p-Si (100) substrate with the help of electron beam physical vapor deposition technique and its structural, electrical and magnetic properties have been experimentally investigated in details. The electronic- and magneto-transport properties at various isothermal conditions have been studied in the temperature regime of 78–300 K. The current–voltage (I–V) characteristics of the junction show an excellent rectifying magnetic tunnel diode-like behavior throughout that temperature regime. The current (I) across the junction has been found to decrease with the application of a magnetic field parallel to the plane of the CMS film clearly indicating positive junction magnetoresistance (JMR) of the heterostructure. When forward dc bias is applied to the heterostructure, the I–V characteristics are highly influenced on turning on the field B = 0.5 T at 78 K, and the forward current reduces abruptly (99.2% current reduction at 3 V) which is nearly equal to the order of the magnitude of the current observed in the reverse bias. Hence, our Co2MnSi/SiO2/p-Si heterostructure can perform in off (Ioff)/on (Ion) states with the application of non-zero/zero magnetic field like a spin valve at low temperature (78 K).

Spin transport and temperature-dependent giant positive junction magnetoresistance in CoFe2O4/SiO2/p-Si heterostructure

The observation of giant positive junction magnetoresistance (JMR) in our cobalt ferrite (CFO)/p-Si heterojunction has been reported here. The pulsed laser deposition technique has been used for fabrication of the heterojunction. The junction confirms a very good rectifying magnetic diode like behavior at low temperature, whereas at high temperatures the junction shows nonlinear I–V characteristics. The magnetic field-dependent magnetoresistance (MR) of both CFO film and across the heterojunction have been studied in detail. The CFO film shows negative MR behavior, whereas the junction shows large positive JMR behavior throughout the temperature range. The spin lifetime (142 ps) and spin diffusion length (331 nm) have been estimated of the heterostructure at 10 K. The highest JMR value (~1600 %) has been observed at 10 K, and it gradually decreases at higher temperature range. The origin of positive JMR in our heterojunction has been best explained by the standard spin injection theory.

Low temperature junction magnetoresistance properties of Co0.65Zn0.35Fe2O4/SiO2/p-Si magnetic diode like heterostructure for spin-electronics

The magnetic heterojunction diode has been fabricated by growing Co0.65Zn0.35Fe2O4 (CZFO) on well cleaned p-Si substrate using pulsed laser deposition technique, and its behavior under magnetic field is experimentally studied in details. The magnetic field dependent current–voltage characteristics (I–V) have been studied at different isothermal conditions in the range of 5–300K. The junction shows magnetic diode like rectifying behavior at low temperature, whereas at high temperatures the junction shows nonlinear I–V characteristics. Magnetic field shows a strong effect on junction resistance (CZFO/p-Si). It is interesting that the positive junction magnetoresistance (MR) thus produced, remains very large at low temperature regime (590% at 5K) and gradually decreases at higher temperatures. In contrast, CZFO magnetic thin film shows negative MR behavior, whereas the junction shows large positive junction magnetoresistance (JMR) behavior throughout the temperature range. The origin of JMR has been best explained by standard spin injection theory. The temperature dependent spin life time (τ) has been estimated for our heterostructure. The value of τ decreases with increasing temperature. The spin life time (183ps), spin polarization (0.71) and spin diffusion length (375nm) have been estimated of the heterostructure at 10K.

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.

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.

Room temperature giant positive junction magnetoresistance of NiFe2O4/n-Si heterojunction for spintronics application

Electronic- and magnetic-transport properties of NiFe2O4 (NFO)–SiO2–Si heterojunction fabricated by depositing NFO thin films on silicon substrates with the intermediate native oxide (SiO2) layer have been investigated in details. The current–voltage (I–V) characteristics across the junction have been recorded in the temperature range of 10–300K. All I–V curves show non-linear behavior throughout the temperature range. The dominating current transport mechanism is found to be temperature dependent tunneling assisted by Frenkel–Poole type emission. In this paper, we report the junction magnetoresistance (JMR) properties of this heterojunction in the temperature range of 10–300K. With increasing temperature, the JMR of the heterojunction increases accordingly. The high positive JMR (~54%) has been observed at room temperature (RT). The origin of high positive JMR at RT is attributed to efficient spin-polarized carrier transport across the junction.

Temperature dependent spin injection properties of the Ni nanodots embedded metallic TiN matrix and p-Si heterojunction

A detailed experimental investigation on magnetic field dependent electronic transport across epitaxial Ni nanoparticles embedded in metallic epitaxial TiN matrix grown on p-type (001) Si substrate heterojunction employing sequential exposure of pulsed excimer laser is reported here. The non-linear current–voltage characteristics along with good rectifying diode like behavior of the junction have been obtained in the range of 100–300K. The ideality factor, reverse saturation current, series resistance and turn-on voltages have been estimated for the heterojunction at different operating temperatures. The dominating current transport mechanism is found to be temperature dependent tunneling assisted Frenkel–Poole type emission. A crossover from negative to positive junction magnetoresistance (JMR) has been observed at ~190K (blocking temperature of the Ni nanodots). The JMR attains a peak with high positive JMR value at 250K, the origin of which has been best explained using standard spin injection theory.

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 highest spin relaxation near 250 K. The junction magnetoresistive properties have been explained using the standard spin injection mechanism through the magnetic p-n junction. Junction magnetoresistance dies out with the increase of doping concentrations in all the three type of metal-semiconductor type junctions due to the less non equilibrium population of polarized electrons.

Sign Reversal of Junction Magnetoresistance in p-La0.7Ca0.3MnO3/SiO2/n-Si Heterostructure: A Possibility in Spintronics Application

We have fabricated a p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure, consisting of a p-type manganite (La0.7Ca0.3MnO3) and n-type Si with a interfacial layer of SiO2 with typical thickness of about 9 nm using pulsed laser deposition technique. The junction exhibits rectifying behavior over the temperature range of 10-300 K with rectification factor 52 at room temperature. Investigation on the electrical properties of p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure exhibits nonlinear J-V characteristics in a wide temperature range. A crossover from negative to positive junction magnetoresistance (JMR) is observed in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure in current perpendicular to film plane (CPP) geometry. The temperature dependent sign of junction magnetoresistance of the heterojunction has been investigated carefully in details. It is found that the junction exhibits the positive junction magnetoresistance when the temperature is greater than the ferromagnetic to paramagnetic transition temperature (Tc) of the top highly spin-polarized half-metallic ferromagnetic La0.7Ca0.3MnO3 manganite film layer. The relation between junction magnetoresistance and external magnetic field is found to be of (delta rho/rho approximately equal alphaHbeta) type having both alpha and beta temperature dependent. We attribute the emergence of negative JMR at lower temperature (< Tc) and positive JMR at higher temperature (> Tc) to the quantum mechanical tunneling transport mechanism across the heterojunction. Our results might be very useful to fabricate artificial devices using the manganite-based heterojunction grown on single crystalline n-Si (100) in spintronics device applications.

Magnetic Schottky diode exploiting spin polarized transport in Co/p-Si heterostructure

Magnetic Schottky heterojunction fabricated from Co/p-Si is investigated. The diode showed proper rectifying property at all temperatures and evolution of a giant positive junction magnetoresistance is observed at temperatures below 50 K. Based on a simplified band structure, the spin polarization of the device is determined to be ∼31% at 10 K. A phenomenological model is proposed to explain the observed spintronic behavior of the device.

Magnetic diode exploiting giant positive magnetoresistance in ferrite/semiconductor heterostructures

Fe 3 O 4 / p-Si and NiFe2O4/p-Si heterostructures were fabricated and their electrotransport and magnetotransport properties were studied. Both heterostructures showed rectifying as well as spin valve property below a critical temperature of 50 K which is independent of Curie temperature of magnetic films. Fe3O4/p-Si and NiFe2O4/p-Si heterostructures show giant positive junction magnetoresistance (JMR) of 2000% and 200% at 10 K, respectively. The JMR for Fe3O4/p-Si saturates at a much lower magnetic field compared to the other heterostructures, thus making it a better choice for magnetic diode.

Room temperature enhanced positive magnetoresistance in Pt and carrier induced Zn(Fe)O and Zn(Fe,Al)O dilute magnetic semiconductors junction

Epitaxial films of ZnO doped with magnetic ion Fe and, in some cases, with 1% Al show clear evidence of room temperature ferromagnetic ordering. The dilute magnetic semiconducting films are n-type in nature. The magnetic moment depends on the carrier concentration of the films. All the films show non-ohmic behavior with Pt metal junction. The observed J–V behavior of Al incorporated films are found to be mainly due to thermionic emission. Except pure ZnO, the junction J–V changes under magnetic field for all the junctions, and shows reasonably high positive junction magnetoresistance at room temperature. The magnitude of junction magnetoresistance is found to depend on the magnitude of the magnetic moment of the dilute magnetic semiconductor films. These properties have been best explained through the standard spin injection theory.