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As magnetic tunnel junction (MTJ) cells for magnetoresistive random access memory (MRAM) are reduced in size, the presence of a magnetization vortex seriously interferes with switching selectivity. We prepared 0.3 μm×0.8 μm, nearly rectangular shape MTJs consisted of PtMn/CoFe/Ru/CoFe/AlOx/NiFe t (t=3,4.5, and 6 nm). Both at-field and remanent state measurements at 0.4 V were conducted to distinguish kinks originating from vortex and domain wall pinning. In addition, we measured samples at various temperatures (from room temperature to 500 K), and with various hard axis fields (from 0 to 90 Oe). As temperature increased, average switching fields decreased, more rapidly for t=6 nm junctions, but kinks were not eliminated completely. When the hard axis field reached about 40-60 Oe, nearly kink-free switching was possible for t=6 nm MTJs.