We have investigated the microstructure and local chemistry of Ta/Ru/Ta/CoFeB/MgO/CoFeB/Ta/Ru magnetic tunnel junctions with different values of tunneling magnetoresistance (TMR) as a result of annealing at different temperatures. Annealing at 500 °C led to the templated crystallization of the amorphous CoFeB layer having coherent interfaces with MgO grains with an orientation relationship of ⟨001⟩[011]MgO∥⟨001⟩[001]CoFe, and the B rejected from crystallized CoFeB was found to be dissolved in upper amorphous Ta layers and segregated in the bottom crystalline Ta layer. Annealing at 600 °C led to the dissolution of 3–4 at. % Ta in the MgO barrier, and B was found to be segregated at the CoFeB/MgO and Ta/Ru interfaces as a result of the crystallization of the top amorphous Ta layer. Further degradation in TMR of the samples annealed at 650 °C results from the loss of bcc-CoFe (001) texture in the bottom CoFeB electrode due to the pronounced Ta diffusion into the CoFe/MgO/CoFe layers.

The microstructure of pseudo spin-valve magnetic tunnel junctions (MTJs) comprising a stacking structure of Ta/Ru/Ta/CoFeB/MgO/CoFeB/ with and without X = Pd, Ti, Ta fabricated on thermally oxidized Si wafer with different annealing temperatures, Ta = 250 °C, 300 °C, 400 °C, and 500 °C, has been investigated. The as-deposited MTJs exhibit an amorphous CoFeB structure that crystallizes into bcc Fe-Co (001) from the MgO (001) interface upon annealing at Ta ≥ 250 °C. A bcc Fe-Co (110) crystallizes from the fcc Pd (111) interface. The Fe-Co layer is alloyed with Pd layer at Ta = 500 °C to form an (Fe, Co)-Pd alloy layer, which causes a drastic reduction in the tunneling magnetoresistance (TMR) from 171% to −2.7%. In the Ti capped MTJs, bcc Fe-Co (001) crystallizes from the hcp (001) Ti interface at Ta = 300 °C. Upon further annealing to Ta ≥ 400 °C, the Ti oxidizes to form amorphous Ti-Ox. The rejected B diffuses back to the CoFe layer at Ta = 500 °C that degrades the TMR. On the other hand, the Ta capped MTJs annealed at 300 ≤ Ta ≤ 500 °C show a perfect grain-to-grain epitaxy with an orientation relationship of (001)[110]MgO//(001)[100]CoFe without interdiffusion or oxidation, resulting in the highest TMR value among all the MTJs with various capping layers.

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Thin films of NiFe2O4 have been deposited on various substrates using pulsed laser deposition and the defect structures investigated by transmission electron microscopy. Owing to the simultaneous nucleation of cation-disordered sites during the nonequilibrium growth, the NiFe2O4 films exhibit antiphase domains of ∼20 nm, irrespective of the substrate symmetry. For growth on isostructural spinel substrates, the density of antiphase appears to decrease with decreasing lattice mismatch. Aberration corrected high resolution transmission electron microscopy reveals that the interchange of equivalent tetrahedral cation positions in the host oxygen sublattice as one of the possible mechanisms leading to the formation of antiphase domains.