Abstract
Nanoscale magnetic materials are the basis of emerging technologies to develop novel magnetoelectronic devices. Self-assembly of polystyrene nanospheres is here used to generate 2D hexagonal dot arrays on Fe50Pd50 thin films. This simple technique allows a wide-area patterning of a magnetic thin film. The role of disorder on functional magnetic properties with respect to conventional lithographic techniques is studied. Structural and magnetic characteristics have been investigated in arrays having different geometry (i.e. dot diameters, inter-dot distances and thickness). The interplay among microstructure and magnetization reversal is discussed. Magnetic measurements reveal a vortex domain configuration in all as-prepared films. The original domain structure changes drastically upon thermal annealing performed to promote the transformation of disordered A1 phase into the ordered, tetragonal L10 phase. First-order reversal magnetization curves have been measured to rule out the role of magnetic interaction among crystalline phases characterized by different magnetic coercivity.
Highlights
Development of new materials for applications responding at the need for continuous optimization of performances, energy saving and environment protection is one of the present challenges in material science and is sustained by advances in nanotechnology. [1,2,3,4] Reduced dimensions, aspect ratio and large surface areas indicate that patterned nanostructures may be good candidates for applications in sensors, biomedical chips, and magnetically assisted drug carriers.[5,6,7] In this quest for nanoscale, novel materials with multi-functional magnetic properties, nano-elements may be fabricated by controlling shape and size
The results of the patterning process obtained by using polystyrene nanospheres having initial diameter about 220 and 500 nm are visible in Figure 3(a) and (c), respectively, where scanning electron microscopy (SEM) corresponding images are reported
The degree of ordering was evaluated by fast Fourier transformation (FFT) and the corresponding 2D FFT image of the array shown in Figure 3(a) revealed a well-ordered hexagonal diffraction pattern
Summary
Development of new materials for applications responding at the need for continuous optimization of performances, energy saving and environment protection is one of the present challenges in material science and is sustained by advances in nanotechnology. [1,2,3,4] Reduced dimensions, aspect ratio and large surface areas indicate that patterned nanostructures may be good candidates for applications in sensors, biomedical chips, and magnetically assisted drug carriers.[5,6,7] In this quest for nanoscale, novel materials with multi-functional magnetic properties, nano-elements may be fabricated by controlling shape and size. Self-assembling methods provide new routes for the large-scale and inexpensive production of nanodevices This technique is widely used to design masks for patterning nanostructures on thin films surface by using polymeric spheres (i.e. polystyrene nanospheres and di-block copolymers) [14,15] and has been shown to be effective in designing dot arrays on several magnetic thin films.[16,17] Arrays of nanodots having chemical compositions characterized by high magnetic anisotropy values (i.e. FePt and FePd alloys) have been the subject of intensive research due to their application in information storage devices (i.e. hard disks and magnetoresistive random-access memory).[18,19] In such binary systems, the fraction of high anisotropy, ordered-L10 to disordered-A1 phase alloys strongly depends on film stoichiometry and thickness given the growth parameters (i.e. substrate, deposition temperature, deposition rate, and pressure).[20,21] Subsequent thermal treatments have been shown to increase the magnetic anisotropy value by completing the A1 to L10 phase transformation.[22,23] In order to assess if large-area patterning techniques can represent a valid alternative to electron-beam nanolithography, a careful balance among viability, intrinsic lattice disorder due to self-arrangement, and its effect on functional magnetic properties has yet to be fully investigated. Magnetization reversal has been carefully studied by magnetization curves and magnetic force microscopy and explained taking into account the nanodot microstructure
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