Self-organizing of spherical MnO and multipods FePt and CoPt nanoparticles in superlattice-type membranes for ultrahigh density magnetic recording

Abstract

Self-assembled ferromagnetic metallic nanoparticle (NP) systems have received considerable attention as potential candidates for ultra-high density magnetic recording (UHMR) applications. However, this application has been limited due to magnetic alignment, since the axes of easy magnetization of spherical NP are randomly oriented in three directions during the self-organizing system on the substrate. In order to overcome these limitations, synthetic methods to produce elongated FePt NP in a face centered cubic phase (fcc) was developed, but the annealing required for the phase transformation from fcc to fct (tetragonal phase), which present hard ferromagnetic characteristics, results sintering and acicular form loss. The state of the art concerning the development of the next generation of the magnetic media shows that much effort has been focused to find solutions to the three main actual challengers: (i) sintering of the individual NP in the media manufacture during the thermal annealing; (ii) well-defined positioning of the particle and interparticle separation maintenance, and (iii) appropriated magnetic alignment allowing the perpendicular magnetic media manufacture with ultra-high density. More recently, arrangements to maintain the positioning of NP over long distances in 2D have been reported through the co-assembly of FePt and MnO into the NaCl-type binary NP superlattice (BNSL). Such arrangements are made in the membrane form by using a newly developed approach called liquid-air interfacial assembly of multicomponent and controlling the FePt / MnO nanoparticles ratio. Heat treatment of BNSL-type membranes at 650 ° C, preserves the ordered structure resulting in membranes with ferromagnetic coercivity as high as 5 kOe at room temperature. However, the problem with the magnetic alignment is recurring, which provide difficulties in obtaining systems that enable the manufacture of recording media for ultra-high density. Our research group has experience in the acicular FePt nanoparticle synthesis, as well as, in the spherical MnO nanoparticle preparation. Thus, this master's project, linked to the project Young Investigator (Proc. FAPESP 07/07919-9 - JP) entitled "Colloidal magnetic nanocrystals: synthesis of self-assembled and macromolecules-functionalized nanospheres, nanowires, and nanorods for advanced magnetic recording, biotechnological, and biomedical applications", is proposed use the our previous acquired knowledge in these nanoparticles synthesis and combine it using the interfacial liquid-ar self-assembling approach to obtain nanostructured NaCl-type BNSL membranes. After that, resulting membranes will be annealed at temperatures around 600-650 ° C in order to form superlattices containing acicular well-positioned FePt nanoparticles. The expectative using this procedure is keep the long-range-ordered fct-FePt nanoparticles, as well as prevent the sintering of nanoparticles as observed in studies involving spherical nanoparticles. In addition, and more important, it is expected that the presence of the acicular FePt nanoparticles can maintain the longitudinal axis order due to the superlattice formation and thus, minimizing or even solving the magnetic alignment challenge.