TEM Investigation Of Microstructure Effect On Pt_0.55Mn_0.45/Ni₈₀Fe₂₀ Systemn By Nanometer Cr Layer Addition Into PtMn Film

The structures of Pt0.55Mn0.45-Cr /Ni80Fe20 films and Pt0.55Mn0.45/Ni80Fe20 films grown on (001) Si substrates by dc magnetron sputtering are investigated by transmission electron microscopy (TEM),high-resolution electron microscopy (HREM) and x-ray diffraction methods. The plane-view and cross-sectional specimens was prepared respectively and the sample in the as-deposited state and upon annealing are observed systematically. The results are as follows:It is indicated that the grain distribution of Pt0.55Mn0.45 film is not uniform and the rang of grain size is from 20nm to 80nm in the plane-view bright-field TEM images. On the other hand Cr addition into Pt0.55Mn0.45 film by inserting thin Cr layers was found to have uniform grains and the rang of grain size is from 20nm to 50nm. It is found that Pt0.55Mn0.45 film has smaller grain by Cr addition . It is shown that the growth features of Pt0.55Mn0.45-Cr /Ni80Fe20 films and Pt0.55Mn0.45/Ni80Fe20 films are the same columnar grain in the cross-section bright-field TEM images and the crystallographic orientation of Pt0.55Mn0.45 film is the same as which of NiFe film. Some of columnar grain of Pt0.55Mn0.45-Cr is divided by the boundarys which are caused by inserting thin Cr layers. The analysis of XRD pattern and the electron diffraction polycraystalling rings shows that the enhancement of exchange bias is due to the c/a ratio of the PtMn film increase associated with the PtMn lattice distortion by inserting Cr layers. The electron diffraction of PtMn-Cr annealed film shows that the existence of many Moire fringes implies good texture of both NiFe and PtMn-Cr grains. It is seen that the excellent PtMn-Cr texture means good crystalline order and high composition of the fcc phase which coexists with the tetragonal phase in polycrystalline PtMn-Cr films.The investigation of cross-sectional specimens by high-resolution electron microscopy (HREM) shows that in rich-Cr areas which are caused by the Cr thin layers is not continuous. It is shown that the phenomenon for crystallographic orientation on (111) texture randomly and the crystallographic orientation on (111) texture transformation from a fct(111) to a fct (110).It is because that Cr plane form a ordering phase which ascribes to the nucleation of crystallographic orientation on (110) Pt0.55Mn0.45-Cr (5 vol %) texture. This is one of the reasons that the exchange bias and thermal property of Pt0.55Mn0.45-Cr /NiFe films enhance greatly, which is caused by larger exchange coupling of crystallographic orientation on (110) Pt0.55Mn0.45-Cr . In summary the structure changes of Pt0.55Mn0.45 /Ni80Fe20 films by inserting Cr layers lead to the enhancement of exchange bias.