Fangzhi Li

Thermal stability of Ir-Mn∕Co-Fe-B∕Al-O∕Co-Fe-B tunnel junctions

The thermal stability of magnetic tunnel junctions with structures of Ta(5)∕Cu(30)∕Ta(5)∕Ni79Fe21(5)∕Ir22Mn78(12)∕Co62Fe20B18(4)∕Al(0.8)-oxide∕Co62Fe20B18(4)∕Cu(30)∕Ta(5) (thicknesses unit in nanometers) has been investigated. The tunnel magnetoresistance (TMR) shows a large increase up to 54.4% after annealing at 265 °C due to the improved characteristic properties of the barrier and the interface between the barrier and the ferromagnetic electrodes. The TMR was observed to decrease drastically above the annealing temperature of 310 °C accompanied by a notable increase of junction resistance and coercivity of the free layer. The amorphous Co62Fe20B18 layers seem to behave as a barrier of diffusion, preventing the migration of Mn or Cu atoms into the interface between the barrier and the ferromagnetic layers. This may cause the drastic decrease of TMR due to the deterioration of the barrier and its interface with Co62Fe20B18 layers. The observed crystallization in the amorphous Co62Fe20B18 layers is consi...

Raman spectrometry study of phase stability and phonon anharmonicity of Al3BC3 at elevated temperatures and high pressures

In situ Raman spectra of Al3BC3 have been measured at elevated temperatures of up to 1000 °C and high pressures of up to 32 GPa. It is shown that there are no abnormal phonon shifts when the measurement conditions were up to 1000 °C or up to 27 GPa, which indicates a good structural stability of Al3BC3 at high temperatures and pressures. The Raman active phonon modes were assigned comprehensively to the corresponding vibration modes by first-principles calculations. Interestingly, an abnormal softening of the E1g(559 cm–1) and E2g(578 cm–1) phonon modes were observed when the pressure was higher than 27 GPa. Correlating the results with previous theoretical predictions of polymorphism in Al3BC3, the mode softening at higher pressures might originate from the structural transformation (from hexagonal to tetragonal symmetry) involving changes of Al and C coordination numbers. In addition, the phonon anharmonicity has been investigated by studying the temperature and pressure dependence of the Raman peak shi...

Developments in hot pressing (HP) and hot isostatic pressing (HIP) of ceramic matrix composites

Abstract: This chapter introduces the hot pressing (HP) and hot isostatic pressing (HIP) methods and their application to produce advanced ceramics. Typical oxides, carbides, borides and nitrides are selected to describe the synthesis process. The conclusion is that HP and HIP are good technologies for fabricating dense or single-phase ceramics. Their advantages, disadvantages and future improvements are discussed.