The magnetization reversal in four arrays of micron-size circular holes ͑antidots͒ in a Permalloy film has been studied by means of quantitative magneto-optic Kerr vector magnetometry and magnetic force microscopy. The primitive antidot meshes of the arrays investigated here can be classified as square, rectangular, hexagonal, and oblique. The vector magnetometry data show that the hole arrays induce a magnetic anisotropy completely different from that of the unpatterned film, with new hard axes along the directions connecting nearest neighboring holes. Also the coercive field is strongly affected by the pattern. The results of the vector magnetometry analysis indicate that the reversal process takes place through a collective and periodic domain nucleation and expansion process. The domain structure in the remanent state has been investigated by magnetic force microscopy imaging. The images display well-defined domain structures, which are periodic and commensurate with the holes array.
A method of graphene transfer without metal etching is developed to minimize the contamination of graphene in the transfer process and to endow the transfer process with a greater degree of freedom. The method involves direct delamination of single-layer graphene from a growth substrate, resulting in transferred graphene with nearly zero Dirac voltage due to the absence of residues that would originate from metal etching. Several demonstrations are also presented to show the high degree of freedom and the resulting versatility of this transfer method.
Recent ferromagnetic-resonance ͑FMR͒ measurements and related simulations on antidot structures suggested the existence of spatially localized modes. In this report we confirm the existence of these modes using time-resolved Kerr microscopy ͑TRKM͒ as a local probe of the magnetodynamics. FMR measurements on an antidot array ͑a 40-nm-thick permalloy film with a hole size of 1.5 m and a hole lattice spacing of 3 m ϫ 5 m͒ at frequencies between 10 and 35 GHz reveal two main resonances, whose relative amplitudes and orthogonal uniaxial in-plane anisotropies suggest the existence of modes localized between holes along each of the principal axes. TRKM measurements in applied fields ranging from 100 to 600 Oe show explicitly the existence of these two modes-one at low frequency between the holes along the short axis and one at higher frequency between the holes along the long axis. TRKM also reveals additional mode structure, most notably a low-frequency mode localized along the edges of the antidots, similar to the edge modes observed in magnetic wires.
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