title: High-resolution imaging of remanent state and magnetization reversal of superdomain structures in high-density cobalt antidot arrays.
abstract: Remanent state and magnetization reversal processes of a series of cobalt antidot arrays with a fixed hole diameter (d ≈ 55 nm) and an array periodicity (p) ranging between 95 and 524 nm were studied by in situ Lorentz microscopy (LM) as a function of the magnetic field. At remanence, defocused LM images showed the periodicity dependence of the magnetic states inside the lattice. A remarkable transition was observed in the type of domain structures as a function of p: for the large periodicities (p > 300 nm), conventional 90° and 180° domain walls were formed, whereas in small-period antidot arrays (p ≦ 160 nm) magnetic superdomain walls (SDWs) were nucleated to separate regions with different average magnetization direction, the so-called magnetic superdomains. In the SDW regime, a low-frequency Fourier filtering method was implemented to allow a quantitative analysis of the LM images by the transport of intensity equation method. In situ LM experiments under applied magnetic fields were performed to study the reversal magnetization process in a particular array (p = 160 nm), and clear differences were observed as a function of the magnetic field orientation. The switching process under magnetic fields parallel to the horizontal antidot rows occurs in two stages: the system first nucleates and propagates horizontal SDWs, parallel to the field. Then, at higher magnetic fields, vertical SDWs, perpendicular to the field, appear before saturation. When the magnetic field is applied at 45° with respect to the antidot rows, both horizontal and vertical SDWs are nucleated and propagated simultaneously. All the experiments were successfully correlated with micromagnetic simulations. The current study sheds new light on the magnetization reversal processes of antidot arrays and opens new possibilities of exploiting the potential of high-resolution in situ LM and new data analysis procedures to probe magnetization processes in nanomagnetism, particularly in periodic arrays of nanomagnets.
authors.affiliation: Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia de Aragón (INA), Universidad de Zaragoza, 50018 Zaragoza, Spain. Departamento de Física de la Materia Condensada, Universidad de Zaragoza, 50009 Zaragoza, Spain. Transpyrenean Associated Laboratory for Electron Microscopy (TALEM), CEMES-INA, CNRS-Universidad de Zaragoza, Toulouse, France. CEMES-CNRS 29, rue Jeanne Marvig, B.P. 94347 F-31055, Toulouse Cedex, France.
authors.forename: L A
authors.initials: LA
authors.lastname: Rodríguez
authors.forename: C
authors.initials: C
authors.lastname: Magén
authors.forename: E
authors.initials: E
authors.lastname: Snoeck
authors.forename: C
authors.initials: C
authors.lastname: Gatel
authors.forename: C
authors.initials: C
authors.lastname: Castán-Guerrero
authors.forename: J
authors.initials: J
authors.lastname: Sesé
authors.forename: L M
authors.initials: LM
authors.lastname: García
authors.forename: J
authors.initials: J
authors.lastname: Herrero-Albillos
authors.forename: J
authors.initials: J
authors.lastname: Bartolomé
authors.forename: F
authors.initials: F
authors.lastname: Bartolomé
authors.forename: M R
authors.initials: MR
authors.lastname: Ibarra