We report on the marked change in magnetic anisotropy and magnetization reversal in Co 50 Fe 50 /[Pb(Mg 1/3 Nb 2/3 O 3 )] 1%x -[PbTiO 3 ] x (PMN-PT) and Co 43 Ni 57 /PMN-PT heterostructures under an electric field. For the Co 50 Fe 50 /PMN-PT structure, the electric-field-induced magnetic anisotropy field can be as large as 1.2 kOe at 12 kV/cm, corresponding to a magnetoelectric coefficient of 100 Oe cm/kV. In the Co 43 Ni 57 /PMN-PT heterostructure, the electric-field-induced anisotropy has a sign opposite to that in Co 50 Fe 50 /PMN-PT. As a result, in the [CoNi/Cu/CoFe/Cu] n / PMN-PT heterostructure, the parallel magnetic moment between two magnetic layers in the initial state may become perpendicular under an electric field. On the basis of these discussions, a voltage-write magnetoelectric memory device model is proposed.
The effect of electric field (E-field) on the magnetism of FePt thin films in FePt/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) heterostructures was investigated by anomalous Hall effect measurement. For FePt films of different thicknesses, the coercivity vs E-field curves show a typical butterfly-like loop behavior. Further results indicate that the coercivity variation is composed of the volatile symmetrical butterfly-like loop and nonvolatile hysteresis loop-like parts, which originate from the volatile and nonvolatile strains induced by the E-field in the PMN–PT(001) substrate, respectively. No significant difference has been observed after inserting a 2 nm W interlayer, suggesting that the charge-mediated coercivity variation is negligible in FePt/PMN–PT heterostructures.
Films with a structure of Ta (5 nm)/Co20Fe60B20 (0.8–1.5 nm)/MgO (1 nm)/Ta (1 nm) were deposited on Corning glass substrates by magnetron sputtering. The as-deposited films with CoFeB layer thickness from 0.8 to 1.3 nm show perpendicular magnetic anisotropy (PMA). After annealing at a proper temperature, the PMA of the films can be enhanced remarkably. A maximum effective anisotropy field of up to 9 kOe was obtained for 1.0- and 1.1-nm-thick CoFeB layers annealed at an optimum temperature of 300 °C. A 4-kOe magnetic field was applied during annealing to study its effect on the PMA of the CoFeB layers. The results confirmed that applying a perpendicular magnetic field during annealing did not improve the maximum PMA of the films, but it did enhance the PMA of the thinner films at a lower annealing temperature.
A superconducting
joint architecture to join unreacted carbon-doped
multifilament magnesium diboride (MgB2) wires with the
functionality to screen external magnetic fields for magnetic resonance
imaging (MRI) magnet applications is proposed. The intrinsic diamagnetic
property of a superconducting MgB2 bulk was exploited to
produce a magnetic field screening effect around the current transfer
path within the joint. Unprecedentedly, the joint fabricated using
this novel architecture was able to screen magnetic fields up to 1.5
T at 20 K and up to 2 T at 15 K and thereby almost nullified the effect
of the applied magnetic field by maintaining a constant critical current
(I
c). The joint showed an I
c of 30.8 A in 1.5 T at 20 K and an ultralow resistance
of about 3.32 × 10–14 Ω at 20 K in a
self-field. The magnetic field screening effect shown by the MgB2 joint is expected to be extremely valuable for MRI magnet
applications, where the I
c of the joints
is lower than the I
c of the connected
MgB2 wires in a given magnetic field and temperature.
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