The perpendicular magnetic anisotropy (PMA) properties of Pt/Co/MgO trilayers are investigated as a function of the MgO sputtering power (PMgO) and its thickness (tMgO), both of which are important parameters affecting the degree of oxygen interpenetration into Co during sputtering. A strong PMA is achieved at small values of PMgO and tMgO, where the oxygen interpenetration into Co is expected to be small. The range of oxygen interpenetration is relatively extended in such a way that it affects both the Pt/Co and Co/MgO interfaces. The PMA properties of as-deposited samples are improved by post-annealing for temperatures up to 400 °C examined in this study, probably due to the diffusion of the interpenetrated oxygen atoms toward the Co/MgO interface. In a structure of Pt/Co (0.6 nm)/MgO (2 nm), which is fabricated at PMgO = 50 W and then annealed at 400 °C, a huge saturation field is achieved (over 40 kOe) indicating a very strong PMA. Between the two interfaces of Pt/Co and Co/MgO, the PMA is mainly due to the former in the as-deposited state, but the contribution of the latter increases with the increase in the annealing temperature.

A strong perpendicular magnetic anisotropy is formed in unit structures containing a thick CoFeB layer (2 nm) that are suitable for an MgO-based magnetic tunnel junction. The value of the coercivity, measured under perpendicular applied magnetic fields, is as high as 1050 Oe after annealing under optimum conditions. The intermixing between the Pd and the CoFeB and a low saturation magnetization of the Co-rich CoFeB layer are considered to be responsible for the strong perpendicular magnetic anisotropy.

The changes in the magnetic dead layer (MDL) and saturation magnetization of the CoFeB layers are investigated as a function of the annealing temperature for four different unit structures, that are relevant to the synthetic ferrimagnetic free structure in MgO-based magnetic tunnel junctions. The MDL results for these unit structures are then converted into those for the constituent interfaces of the free structure. Most of the changes in the MDL thickness occur during annealing at a low temperature of 150 °C while those in the saturation magnetization occur at a high annealing temperature of 350 °C. These results for the MDL and saturation magnetization are critically tested by using the synthetic ferrimagnetic free structures with various thickness asymmetries. The observed switching properties of these tested structures are in good agreement with those expected from the results for the MDL and saturation magnetization, confirming the accuracy of the present results. The accuracy of the saturation magnetization is further confirmed by ferromagnetic resonance experiments.

Three-dimensional numerical calculations based on the finite element method are performed to calculate the increase of temperature caused by Joule heating during the current-induced magnetization switching of an MgO-based magnetic tunnel junction. The increase of temperature is found to be significantly large (the maximum being 145K) at critical conditions for the current-induced magnetization switching. The temperature increase also differs greatly, depending on the critical condition, requiring a correction in calculating the thermal stability parameter using the Slonczewski equation. After the correction, the thermal stability parameter increases substantially from 67 to 76.

ABSTRACT:A new mixing process was explored to increase further the fracture toughness and to investigate the toughening mechanisms of epoxy/nylon blend. In this process, without mechanical mixing, the mixtures of epoxy and premade nylon 6 powder were heated without the curing agent to specific temperatures, referred to as the "mixing temperature." For epoxy/nylon blends, at sufficiently high temperatures, a semi-interpenetrating network-like structure can be developed at the interphase via the reaction between the amine end group and the epoxide group. The depth of interphase and the extent of reaction depends on the mixing temperature. The strong dependency of the fracture energy on mixing temperature reveals the positive effect of the newly developed structure at the interphase. The increase of fracture toughness is possibly due to the enhanced crack fingering bifurcation/deflection mechanism resulting from the lamellae developed in the interphase and the enhanced plastic deformation of epoxy as a result of preyielding of the interphase.