Electrodeposited multilayered nanowires grown within a polycarbonate membrane constitute a new medium in which giant magnetoresistance (GMR) perpendicular to the plane of the multilayers can be measured. These structures can exhibit a perpendicular GMR of at least 22% at ambient temperature. We performed detailed studies both of reversible magnetization and of irreversible remanent magnetization curves for CoNiCu/Cu/CoNiCu multilayered and CoNiCu pulse-deposited nanowire systems with Co:Ni ratios of 6:4 and 7:3 respectively in the range 10 - 290 K, allowing the magnetic phases of these structures to be identified. Shape anisotropy in the pulse-deposited nanowire and inter-layer coupling in the multilayered nanowire are shown to make important contributions to the magnetic properties. Dipolar-like interactions are found to predominate in both nanowire systems. Magnetic force microscope (MFM) images of individual multilayered nanowires exhibit a contrast consistent with there being a soft magnetization parallel to the layers. Switching of the magnetic layers in the multilayered structure into the direction of the MFM tip's stray field is observed.

An alternative interpretation of the contrast in magnetic force microscopy images is proposed. The new approach is based on rewriting the interaction energy between tip and sample as a convolution of the scalar potential of the tip field with the magnetic “charges” of the sample. The second derivative of the scalar potential with respect to the tip–sample distance has to be inserted to obtain the MFM image in the force gradient mode. By demonstrating the potential of conventional tip geometries to be sharply localized in particular for the mentioned derivative we show that magnetic force microscopy is in the weak interaction limit effectively a method for the high resolution observation of magnetic charges. The virtual identity of a simulated MFM image derived from the numerically calculated stray field, and the corresponding charge image demonstrates the validity of the new approach.

Articles you may be interested inCross-relaxation between macromolecular and solvent spins: The role of long-range dipole couplings Role of dynamic exchange coupling in magnetic relaxations of metallic multilayer films (invited) J. Appl. Phys. 93, 7545 (2003); 10.1063/1.1543852Dipoleexchange spin wave spectra of exchangecoupled magnetic multilayers calculated by transfer matrix formalism Thii work considers the role of magnet.ic dipole coupling in multilayers typically comprising a ferromagnetic material separated by a nonmagnetic metal spacer, e.g., NiFe!Ta. It has been suggested previously that dipolar fields may play an important role in the coupling of magnetic layers through a nonmagnetic spacer, in particular where surface roughness at the interface is significant. This work considers a first-order calculation of the dipole coupling energy and magnetic field between two adjacent layers. It is shown that dipole coupling energies originating from surface corrugations can behave in the same manner as a coercive field in terms of dependence on nonmagnetic spacer thickness and the degree of roughness. Interestingly, calculations also show that both ferromagnetic-and antiferromagnetic-like coupling can be explained in terms of this model. The role of the spacer thickness, magnetic layer thickness, and the form of the roughness is discussed.

Articles you may be interested inDot-by-dot analysis of magnetization reversal in perpendicular patterned CoCrPt medium by using magnetic force microscopy