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We have investigated topological spin textures in the ferromagnetic metallic phase of La0.825Sr0.175MnO3 with the centrosymmetric crystal structure by small-angle electron diffraction (SmAED) and low-temperature Lorentz transmission electron microscopy (TEM) experiments. In-situ Lorentz TEM and SmAED experiments revealed that type-I and type-II magnetic bubbles evolved from magnetic stripe domains with the Bloch-type domain wall by applying vertical magnetic field. Type-I magnetic bubbles with left-handed and right-handed spin helicity were randomly distributed and simultaneously type-II magnetic bubbles are formed locally. The important point about type-I and type-II magnetic bubbles is that their emergence depends strongly on whether perpendicular magnetic field is applied parallel to the magnetic easy axis along the [001] direction. Our experimental results suggested that the stabilization of magnetic bubbles should originate from the long-range dipole-dipole interactions, as opposed to the Dzyaloshinskii-Moriya interaction in helical magnets.

A hollow-cone Foucault (HCF) imaging method using Lorentz microscopy was developed. Hollow-cone illumination was realized by using deflectors above the specimen and an inclined electron beam circulating with respect to the optical axis. The advantage of the HCF method, having the bright and dark-field modes, is that it can simultaneously visualize both magnetic domains and magnetic domain walls under the in-focus condition. Furthermore, schlieren images, obtained under the specific inclination angle of the illumination beam by adjusting the angle between the bright-field and dark-field modes, can qualitatively visualize the electromagnetic fields in spaces around the specimen.

We report application of hole-free phase plate (HFPP) to imaging of magnetic skyrmion lattices. Using HFPP imaging, we observed skyrmions in FeGe, and succeeded in obtaining phase contrast images that reflect the sample magnetization distribution. According to the Aharonov-Bohm effect, the electron phase is shifted by the magnetic flux due to sample magnetization. The differential processing of the intensity in a HFPP image allows us to successfully reconstruct the magnetization map of the skyrmion lattice. Furthermore, the calculated phase shift due to the magnetization of the thin film was consistent with that measured by electron holography experiment, which demonstrates that HFPP imaging can be utilized for analysis of magnetic fields and electrostatic potential distribution at the nanoscale.

Magnetic textures in the ferromagnetic phases of La 1-xSrxMnO3 for 0.15 < x < 0.30 have been investigated by Lorentz microscopy combined with small-angle electron diffraction experiments. Various types of magnetic textures characterized by stripe, plate-shaped, and cylindrical (magnetic bubble) domains were found. Two distinct types of magnetic stripe domains appeared in the orthorhombic structure with an inversion symmetry of La0.825Sr0.175MnO3, depending significantly on magnet ocrystalline anisotropy. Based on in-situ observations as functions of temperature and the strength of the external magnetic field, a magnetic field-temperature phase diagram was constructed, showing the stabilization of magnetic bubbles in the ferromagnetic phase of La0.825Sr0.175MnO3. P.A.C. S numbers: 75.70Kw, 75.47.Lx, 75.78.Fq, 68.37.Lp