Jifan Hu

Room-temperature ferromagnetism in MgO nanocrystalline powders

MgO nanocrystalline powders prepared by sol-gel method present room-temperature ferromagnetism, whereas MgO bulk exhibits diamagnetism. The vacuum annealing of MgO nanocrystalline powders reduces ferromagnetism. The observed room-temperature ferromagnetism in MgO nanocrystalline powders possibly originates from Mg vacancies at/near the surfaces of nanograins. Mg vacancies can induce local magnetic moments. Large concentrations of Mg vacancies at the surfaces of nanograins possibly establish magnetic percolation.

Structure and magnetic properties of TbMn6−xAlxSn6 compounds

In the present work, the influence of the substitution of Al for Mn on the structure and magnetic properties of TbMn6−xAlxSn6 compounds was investigated. With increasing Al concentration the lattice constants a, c, and the unit-cell volume V decrease monotonically. The TbMn6−xAlxSn6 compounds exhibit ferrimagnetic ordering. The magnetic ordering temperature first decreases with increasing Al content up to x=1.5, then increases with further increasing Al content. As for the unsubstituted material, it was found that this series of compounds exhibits a second magnetic transition at lower temperature that is attributed to spin reorientation. The spin-reorientation temperature and the magnetic anisotropy field first decrease with increasing Al content, go through a minimum at x=0.5, then increase with further increasing Al content. The saturation magnetization decreases monotonically with increasing Al content. Two metamagnetic transitions are found in TbMn6Sn6 compounds, one at 0.44 T, and the other at about ...

Giant magnetoimpedance and colossal magnetoresistance in La0.75Sr0.25MnO3 at room temperature

The impedance as well as the resistance and reactance of the La0.75Sr0.25MnO3 manganite increase with increasing ac frequency due to the skin effect of the metal state below Curie temperature. The manganite La0.75Sr0.25MnO3 shows not only the colossal magnetoresistance effect but also the giant magnetoimpedance effect. For the giant magnetoimpedance, the magnetic field influences the impedance by affecting the penetration depth via the transverse permeability, whereas for the colossal magnetoresistance the magnetic field tends to align the local spins, leading to the decrease of the dc resistance via the interplay between a strong electron–phonon coupling and the double exchange effect of spin alignment on electron kinetic energy.

Magnetoimpedance effect in La0.67Ba0.33MnO3 under low dc magnetic fields

Abstract We report the magnetoimpedance effect under dc magnetic fields of tens of Oersteds in La0.67Ba0.33MnO3 polycrystalline sample prepared using the conventional solid state reaction method. The magnetoimpedance, magnetoresistance, and magnetoreactance of La0.67Ba0.33MnO3 have been found to vary sensitively on both the dc magnetic field and ac current frequency. The magnetoimpedance effect observed in the present work reveals a novel aspect of the interplay between magnetism and electronic transport in perovskite Mn oxides, which is of great scientific and technological interest.

Room temperature magnetoresistance in La0.67Sr0.33Mn1-xAlxO3 manganites (x≤0.25)

Abstract An enhancement of the room temperature magnetoresistance induced by the Al substitution in La 0.67 Sr 0.33 Mn 1− x Al x O 3 was observed. A peak of the room temperature magnetoresistance occurs at Al content of x ≈0.05. This enhancement is correlated with the shift of the Curie temperature and metal–insulator transition temperature to near room temperature through the Al substitution. The room temperature magnetoresistance drops again at a large Al content x ⩾0.10, which may be due to the lower metal–insulator transition temperature far from the room temperature.

Coexistence of electric field controlled ferromagnetism and resistive switching for TiO2 film at room temperature

The Ag/TiO2/Nb:SrTiO3/Ag device exhibits the coexistence of electric field controlled ferromagnetism and resistive switching at room temperature. The bipolar resistive switching in Ag/TiO2/Nb:SrTiO3/Ag device may be dominated by the modulation of Schottky-like barrier with the electron injection-trapped/detrapped process at the interface of TiO2/Nb:SrTiO3. We suggest that the electric field-induced magnetization modulation originates mainly from the creation/annihilation of lots of oxygen vacancies in TiO2.

Enhancement of room temperature magnetoresistance in La0.65Sr0.35Mn1−xTxO3 (T=Fe and Ni) manganites

Abstract An enhancement of the room temperature magnetoresistance is induced by the substitution of Fe or Ni for Mn with appropriate content x in La0.65Sr0.35Mn1−xTxO3 (T=Fe and Ni) manganites, since the temperature of metal–insulator transition of La0.65Sr0.35Mn1−xTxO3 can be shifted from a high temperature to near room temperature through the substitution.

The intrinsic magnetic properties of novel R3(Fe,Mo)29 compounds (R=Ce, Nd, Sm, Gd and Y)

Pb(Zr0.53Ti0.47)O-3 (PZT 53/47) is a polycrystalline film with coarse square-shaped grains. The surface morphology can be improved by reducing the cooling rate at the Curie temperature region; however this morphology still does not meet the requirement of device engineering. Pb(Zr0.2Ti0.8)O-3 (PZT 20/80) film has been synthesized, to reduce the lattice mismatch between PZT and substrate. This film has a smooth surface without any evident crystalline features. A TEM of the cross-sectional PZT/YBa2Cu3O7 (YBCO) integrated film shows there is no interaction between the PZT, YBCO and substrate. ZrO2 particles are detected in the PZT film.

Giant magnetoimpedance and permeability in CoFeNiSiB amorphous ribbon

In the present work, the effect of longitudinal and transverse magnetoimpedances connected with the transverse permeability and longitudinal permeability for amorphous ribbons of CoFeNiSiB has been investigated in detail. Our results strongly show that there exists a correlation between the magnetic field dependences of the magnetoimpedance and the magnetic permeability.

Magnetic properties of transition metal doped AlN nanosheet: First-principle studies

We carry out our first-principles calculations within density functional theory to study the 3d transition metal (TM) doped AlN nanosheets. The calculated results indicate that a stoichiometric AlN nanosheet is graphene-like structure and nonmagnetic. The TM impurities can induce magnetic moments, localized mainly on the 3d TM atoms and neighboring N atoms. Our calculated results of TM-doped nanosheet systems indicate a strong interaction between 3d orbit of TM atom and the 2p orbit of N atoms. In addition, the Mn- and Ni-doped AlN nanosheet with half-metal characters seems to be good candidates for spintronic applications. When substituting two Al atoms, the relative energies of the states between ferromagnetic and antiferromagnetic coupling are investigated sufficiently. The exchange coupling of Co- and Ni-doped AlN nanosheets exhibits a transformation with different distances of two TM atoms and that of Cr-, Mn-, and Fe-doped AlN nanosheets is not changed.