Reversal Behavior Of Magnetic Domain In Shape-Controlled Ni₇₅Fe₂₅ Films In-situ TEM

Magnetic tunnel junctions?MTJs?with tunnel magneto-resistance effect?TMR?have become one of the hottest research topics in condensed matter physics,information industry and material science for more than twenty years.However,their further miniaturization in the information industry are recently stuck,including in their important applications of the read-heads of hard-disk drivers?HDDs?and magnetoresistive random access memories?MRAMs?.One of the main reasons is that the real behaviors of the magnetization dynamics in MTJs at the nanoscale is not fully clear so far.In this thesis,I focus on the dynamical behaviors of nanoscale Ni₇₅Fe₂₅ patterns with diverse shapes investigated by a dedicated magneto-electrical holder in situ Lorentz transmission electron microscopy?TEM?with a biprism.The Ni₇₅Fe₂₅ specimens were prepared by high-vacuum sputtering method and milled into the expected geometrical shapes by focused ion beam-scanning electron microscope?FIB-SEM?.The dynamical magnetic reversal processes of the Ni₇₅Fe₂₅nanopatterns were videoed by a Gatan K2 in situ high-speed camera which is equipped onto FEI themis G2 cubed Cs-corrected TEM.The influences of the shapes,sizes and edge defects of the milled nanopatterns on their magnetic reversal mechanism and spin transport behaviors have been studied.This work should be significant for the solution of conquering cell-by-cell variability of MRAM and the high density of MRAM writing current.The main results are summarized as follows:?1?Our dedicated magneto-transport instrument in situ scanning electron microscope?SEM?has een further improved.The technical performance of the updated model was systematically ested,showing a 14 mm movement range with 0.2 nm minimum step resolution,360°rotation bility in plane with 0.003°minimum precision and up to 1800 Oe magnetization field.The agneto-transport behavior of a Ni₇₅Fe₂₅ thin film was dynamically measured in situ SEM.?2?Tens of zigzag and polygonal Ni₇₅Fe₂₅ nanopatterns with different sizes were milled by FIB-SEM.The specimens were then transferred to our dedicated magneto-electrical holder in situ EM.Dynamical magnetic reversal processes of the shape-and size-controlled Ni₇₅Fe₂₅ anopatterns induced by external field were observed in situ C_s-corrected TEM equipped with orentz mode and biprism.Based on the experimental parameters,theoretical reversal ehaviors of the magnetic domains were further simulated to compare with the observed magnetic reversal behaviors.The trend of magnetic flux influenced by edge defects in diverse Ni₇₅Fe₂₅ nanopatterns were obtained.The results show that the shapes and movement behaviors of magnetic domains can be intended to modulate via the shapes of pinnings.It is believed that this work have provided an insight into the influences of the pinning effect of boundary situations of MTJ units on the performance of MTJ devices.