Liu Yong-Sheng

Fabrication, Structural and Magnetic Properties for Aligned MnBi

MnBi compound is fabricated under a magnetic field of 1T, and the c-axis of hexagonal MnBi crystal is aligned parallel to the magnetic field direction. The saturation magnetization Ms decreases with the increase of temperature. At temperatures below 200 K, the coercive field Hc is about 150 Oe, while the coercive field Hc increases with temperature above 200K. From 200K to 300K, the remnant magnetization Mr and the Mr/Ms increase with the temperature. Below 200 K, Mr and Mr/Ms reach roughly a constant value. However, there is an abnormal increase at 100 K in Hc, Mr and Mr/Ms, which comes from a spin-reorientation in MnBi. Magnetization results show the spin-reorientation for MnBi at about 91 K due to the variations of the anisotropy constants.

Influence of Magnetic Scattering and Interface Transparency on Superconductivity Based on a Ferromagnet/Superconductor Heterostructure

We investigate an antiferromagnet/ferromagnet/superconductor/ferromagnet (AF/F/S/F) spin-valve system with nanoscopic scale, described by Usadel equations in the dirty limit. The results show that the superconducting characteristics in the system strongly depend not only on the mutual orientation and thickness of two ferromagnetic layers, but also on the interface transparency and the magnetic scattering. The superconducting critical temperature can exhibit three types of characteristic behaviors with a variation of interface transparency. In particular, the reentrance phenomenon of the superconductivity is observed at the interface transparency ?B?n/?f = 7.1, while the reentrance phenomenon disappears in the presence of magnetic scattering. In addition, it is also found that the introduction of magnetic scattering results in the decrease of the spin-valve effect. The obtained results could provide some practical recommendations for the spin-valve effect in experimental observation.

Crystalline and Magnetic Enhancement of Nanocrystalline MnZn Ferrites Fabricated under a High Magnetic Field

Nanocrystalline Mn0.6Zn0.4Fe2O4 particles are synthesized under magnetic fields of 0 and 6 T, and their structural and magnetic properties are investigated. The magnetic field enhances the grain size and the lattice strain. Magnetic measurements show that the majority of the 6 T nanoparticles are superparamagnetic nearly from 40 to 300 K. It is interesting that the saturation magnetization of the 6 T sample is about 18% and 16% higher than that of the 0 T sample at 120 and 300 K, respectively.

In-Situ Alignment of MnBi Crystals Induced by High Magnetic Field above Curie Temperature

Above Curie temperature, MnBi crystals are aligned in situ along the c-axis in a Bi matrix by a high fabrication magnetic field Hf of 10 T. Magnetic testing shows a pronounced anisotropy in magnetization in directions normal and parallel to the fabrication field, resulting from the alignment. The successful alignment may result from the fact that the easy magnetization direction is along the c-axis of MnBi and the high fabrication field of 10 T is large enough to rotate the MnBi crystal to this direction even though the temperature is above the Curie temperature.

Observation of Dynamic Behavior in YBa 2 Cu 3 O 7−δ /La 0.88 Ca 0.12 MnO 3 Using Femtosecond Optical Pulses

Ultrafast pump-optical probe spectroscopy is used to analyze the carrier dynamic behavior in YBa2Cu3O7—δ/La0.88 Ca0.12MnO3 (YBCO/LCMO) heterostructure. The change in reflectivity ΔR/R is induced and is probed by using pulses of 120 fs duration and photon energy 1.55 eV from a Ti:sapphire laser. For higher laser power fluence (such as 0.5mJ/cm2), the time evolution in transient reflectivity change ΔR/R exhibits three long relaxation processes. We extract the characteristic relaxation time of the different processes by fitting the data and obtain the long characteristic relaxation time which indicates the enhanced proximity effect of the YBCO/LCMO.