Formation of Zero‐Field Magnetic Bubbles and Magnetic Phase Transitions in PbFe12O19 via In Situ Lorentz Microscopy

Abstract

Understanding the magnetic transitions between different noncollinear spin textures under external stimuli is an important topic in modern magnetism. Here, the stripe‐to‐bubble transition is investigated in hexaferrite PbFe12O19 (001) thin plates with a magnetocrystalline anisotropy constant of Ku = 22 × 105 erg cm−3 at room temperature by in situ Lorentz transmission electron microscopy (LTEM) with varying specimen temperature and magnetic field. The LTEM observations reveal that the application and subsequent reduction of a parallel field to the specimen plane at room temperature results in the formation of zero‐field metastable magnetic bubbles. However, the application of an external field perpendicular to the specimen plane did not transform magnetic stripes to bubbles. This is in stark contrast to most perpendicularly magnetized materials that host magnetic bubbles. It is also found that the presence of Bloch lines in stripes induced by the parallel field is crucial for bubble formation. Moreover, in situ heating and cooling experiments for different initial states of magnetic stripes revealed a facilitating role of Bloch lines in the stripe‐to‐bubble transition and the metastable nature of zero‐field bubbles in PbFe12O19 thin films.