H.L. Ge

Influence of bath composition on the electrodeposition of cobalt-molybdenum amorphous alloy thin films

Abstract Cobalt-molybdenum (Co-Mo) amorphous alloy thin films were deposited on copper substrates by the electrochemical method at pH 4.0. Among the experimental electrodeposition parameters, only the concentration ratio of molybdate to cobalt ions ([MoO42−]/[Co2−]) was varied to analyze its influence on the mechanism of induced cobalt-molybdenum codeposition. Voltammetry was one of the main techniques, which was used to examine the voltammetric response, revealing that cobalt-molybdenum codeposition depended on the nature of the species in solution. To correlate the type of the film to the electrochemical response, various cobalt-molybdenum alloy thin films obtained from different [MoO42−]/[Co2+] solutions were tested. Crack-free homogeneous films could be easily obtained from the low molybdate concentrations ([MoO42−]/[Co2+]) ≈0.05) applying low deposition potentials. Moreover, the content of molybdenum up to 30wt% could be obtained from high molybdate concentration; in this case, the films showed cracks. The formation of these cracked films could be predicted from the observed distortions in the curves of electric current-time (j-t) deposition transients. The films with amorphous structure were obtained. The hysteresis loops suggested that the easily magnetized axis was parallel to the surface of the films. A saturation magnetization of 137 emu.g−1 and a coercivity of 87 Oe of the film were obtained when the deposition potential was −1025 mV, and ([MoO42−]/[Co2+]) was 0.05 in solution, which exhibited a nicer soft-magnetic response.

Electrical modulation of magnetism in multiferroic heterostructures at room temperature

Multiferroic heterostructures CoPd/0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (001) (CoPd/PMN–PT) with the thickness of 10xa0nm were fabricated via magnetron sputtering. The effect of electric field on remanent magnetization, coercivity, and magnetization reversal have been subsequently investigated. A large electric field modulation of magnetism is obtained in strain-mediated CoPd/PMN–PT multiferroic heterostructures. Not only the remanent magnetization but also the magnetic coercivity of CoPd film can be effectively modulated by an electric field. Up to 30.7% of magnetization difference is observed by electric field at the vicinity of the magnetic coercivity. Taking the advantage of the different coercivity controlled by electric field, the magnetization reversal can be assisted by electric field. The magnetization reversal process of the CoPd/PMN–PT heterostructure is dominated by the Kondorsky model. Our results provide great opportunities for electric field-controlled magnetic devices.

Surface-effect enhanced magneto-electric coupling in FePt/PMN-PT multiferroic heterostructures

A series of FePt films with different film thickness are deposited on Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) substrates. A standard symmetric ‘Butterfly’ shaped ΔM/M-Edc loops is obtained in 8 nm FePt/PMN-PT heterostrucuture via strain mediated magnetoelectric coupling. For the 3 nm FePt/PMN-PT heterostructure, the loop-like in-plane magnetization (M) -E curve shares a similar shape with the electric polarization of PMN-PT as a function of electric field. The value of MS shows a dramatic change of 30.9% with Edc changing from 0 to 8 kV/cm, this giant magnetoelectric effect in 3 nm FePt/PMN-PT heterostructure results from the remnant polarization induced charge on FePt/PMN-PT interface via the screening charge effect. The enhanced magnetoelectric coupling in thin magnetic/ferroelectric heterostructures opens a promising avenue for the design of ultralow power magnetoelectric devices and information storage devices.

Structure and magnetic properties of L10-MnGa nanoparticles prepared using direct reactions between Mn nanoparticles and Ga

The tetragonal L10-Mn1+xGa (x<0.8) nanoparticles and bcc-Mn23Ga77 nanoparticles with large coercivity were prepared using direct reactions between Mn nanoparticles and Ga at elevated temperatures. The Mn23Ga77 phase was formed at ∼573 K while the L10-structured Mn1+xGa was formed at ∼850 K. After ball-milling, the L10-Mn1+xGa nanoparticles transformed into nano-flakes with enhanced coercivity. The size of the as-prepared Mn23Ga77 nanoparticles is comparable to that of the precursor Mn nanoparticles. An aggregation of the nanoparticles and thus a larger particle size were observed in the L10-Mn1+xGa nanoparticles obtained at 850 K. The size of the L10-Mn1+xGa nano-flakes is reduced to about 200-400 nm with a thickness of ∼20 nm. The coercivity of the Mn23Ga77 nanoparticles and the L10-Mn1+xGa nanoparticles at 300 K reached up to 0.2 T and 0.43 T, respectively. The coercivity of L10-Mn1+xGa ball-milled nano-flakes is 0.59 T at 300 K.