Copyright (c) 2009 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/physicssellmyer Recent documents in David Sellmyer Publications en-us Sat, 12 Sep 2009 23:25:49 PDT 3600 http://digitalcommons.unl.edu/physicssellmyer/219 http://digitalcommons.unl.edu/physicssellmyer/219 Fri, 11 Sep 2009 11:44:23 PDT The reason for the enormous interest in nanomaterials is because they display unique and superior properties that are generally unavailable in conventional macroscopic materials. Gleiter and coworkers [1] first generated a novel solid structure with gas-like disorder, in addition to long-range order (crystalline and quasicrystalline solids) and short-range order (amorphous/glassy solids). Inert-gas condensation (IGC) is a well established nanoparticle production technique [2-4]. Figure 1 shows an IGC system equipped with magnetron sputter source and mass selector that was used in the present work. The ability to control the process parameters to fabricate metal nanoparticles with tailored size, shape, and properties is important for research in this area. Xingzhong Li http://digitalcommons.unl.edu/physicssellmyer/218 http://digitalcommons.unl.edu/physicssellmyer/218 Fri, 11 Sep 2009 11:42:16 PDT Transmission electron microscopy (TEM) imaging and electron diffraction (ED) techniques are widely used in the studies of thin films and nanoparticles. Although various advanced techniques have been well established, such as high-resolution electron microscopy (HREM) and convergent beam electron diffraction (CBED), the conventional TEM imaging and selected-area electron diffraction (SAED) techniques remain the essential methods for microstructure and crystal structure characterization. Digital TEM image processing and quantitative ED analysis (QED) has become one trend for improvements. Recently computer programs [1,2] have been developed for analysis of SAED patterns of polycrystalline phases. In this paper, we report the preliminary results on a TEM/QED study of FePt ultrathin films and Co/CoO core shell particles. Xingzhong Li http://digitalcommons.unl.edu/physicssellmyer/217 http://digitalcommons.unl.edu/physicssellmyer/217 Fri, 11 Sep 2009 11:38:57 PDT FePt films and FePt-based nano-composite films with the high-anisotropy L10 ordered phase have been extensively studied, since they have significant potential for extremely high-density perpendicular magnetic recording media and nano-composite permanent magnets [1]. Recently, new functional films were synthesized with a FePt:C composite layer on top of continuous FePt layer, in order to study the effect of the FePt layer on the ordering, orientation and magnetic properties of the composite layer. Transmission electron microscopy (TEM), together with X-ray diffraction, has been used to check the growth of the double-layered films and to study the microstructure, including the grain size, shape, orientation and distribution. The results have been used as feedback to improve the film synthesis and to analyze the structures related to novel functions of the designed films. In this report, the TEM studies of both single-layered nonepitaxially grown FePt and FePt:C composite L10 phase and double-layered deposition FePt:C/FePt are presented. Xingzhong Li http://digitalcommons.unl.edu/physicssellmyer/216 http://digitalcommons.unl.edu/physicssellmyer/216 Mon, 06 Apr 2009 13:29:03 PDT Magnetically hard Sm2(Co0.8Fe0.2)17 and SmCo5 nanoparticles have been produced by using surfactant-assisted low- and high-energy ball milling techniques. Surfactants prevent the rewelding of the crashed particles during the milling process. Heptane was used as the milling medium and oleic acid as the surfactant. High-energy ball milling experiments took place in a milling vial with carbon steel balls by using an SPEX 8000M high-energy ball milling machine. The coercivity was found to increase with milling time with values of 2.3 kOe for Sm2(Co0.8Fe0.2)17 and 18.6 kOe for SmCo5 after 4 h of milling. Transmission electron microscopy data showed that the milled powders consisted of nanoparticles with an average size of 5-6 nm and a narrow size distribution. Samples deposited on copper coated carbon grid showed self-assembled nanoparticles which could be further aligned when subjected to a magnetic field. Nilly Akdogan http://digitalcommons.unl.edu/physicssellmyer/215 http://digitalcommons.unl.edu/physicssellmyer/215 Mon, 06 Apr 2009 13:29:02 PDT Rapidly solidified Ni54Fe27−2xGa19+2x (x=0, 1, 2, 3, and 4) ferromagnetic shape memory alloys were made by melt-spinning with variation of Fe and Ga contents to report on the martensitic phase transformation, microstructures, and magnetic properties. Rapid solidification produced pure L21 phase by preventing the formation of γ-phase. To study the effect of heat treatment on the phase transitions, microstructures, and the magnetic properties, the melt-spun ribbons were partly heat treated at different temperatures of 800, 900, 1000, 1100, and 1200 K with holding times of 5, 10, and 15 min followed by either water quenching or air cooling. The microstructures of the as-spun ribbons as revealed by electron microscopy studies exhibited a gradual transition from cellular to dendritic structure with increasing Ga concentration and with the presence of some internal martensitic twin bands at higher Ga content. The ribbons exhibited very low coercivity with high saturation magnetization, as high as ~87 em/g (decreasing with Ga concentration). The above-ambient Curie temperature (TC) and the subambient martensitic transition temperature (Tm) were observed to be ~320 and ~195 K, respectively. At higher heat treatment temperatures formation of ductile γ phases was observed. S. Aich http://digitalcommons.unl.edu/physicssellmyer/214 http://digitalcommons.unl.edu/physicssellmyer/214 Mon, 06 Apr 2009 13:29:01 PDT In current extremely high density recording media design, the signal to noise ratio SNR is related to the number of magnetic grains N in a recording bit by SNR = 10 logl0 N .................................... (1) In earlier studies we have found that a metallurgical grain can act as a magnetic grain when grains are magnetically decoupled by a non-magnetic phase [1,2]. Alternatively, several metallurgical grains can be exchange-coupled together when they are small [3]. An ideal morphology is one in which the non-magnetic atoms are segregated at the grain boundaries forming the non-magnetic phase while keeping the grains closely packed. Yi Liu http://digitalcommons.unl.edu/physicssellmyer/213 http://digitalcommons.unl.edu/physicssellmyer/213 Mon, 06 Apr 2009 13:28:59 PDT The critical relationship between microstructure and nanostructure of materials and their magnetic properties has been appreciated for decades. Electromagnetic machinery, permanent magnets, and data recording and electronic devices all have seen steady and sometimes spectacular advances over this period. At the present time the most interesting research in magnetism and magnetic materials arises from new developments in structuring materials on the nanometer length scale. This talk will present recent advances and challenges in furthering this work, with particular attention paid to extremely high density magnetic recording films, exchange-coupled high-energy-product permanent-magnet materials, high-temperature permanent-magnet materials, and self-organized and patterned magnetic nanoarrays. David J. Sellmyer http://digitalcommons.unl.edu/physicssellmyer/212 http://digitalcommons.unl.edu/physicssellmyer/212 Mon, 06 Apr 2009 13:28:58 PDT The great strength of transmission electron microscope (TEM) is its capability to access to both real space (imaging) and reciprocal space (diffraction). Selected reflection imaging (SRI) can relate the diffraction of nanostructured materials with the image, providing information otherwise not possible. The experimental set up of SRI is given by Liu and Sellmyer [I]. In this paper we present some new measurements on nanocomposite magnetic materials. Yi Liu http://digitalcommons.unl.edu/physicssellmyer/211 http://digitalcommons.unl.edu/physicssellmyer/211 Tue, 27 Jan 2009 09:37:02 PST The synthesis, structure, and magnetic properties of a new composite material obtained by the codeposition of polypyrrole and iron, in the galvanostatic mode, using square wave potentials are reported. The effect of electrodeposition conditions (voltage and concentration of the electrolytes) on the magnetic properties of the nanocomposite is analyzed. Mircea Chipara http://digitalcommons.unl.edu/physicssellmyer/210 http://digitalcommons.unl.edu/physicssellmyer/210 Wed, 18 Jun 2008 09:22:58 PDT The structure and magnetic properties of multilayer magnets with a hard phase (HP1 =NdM13.5Dy1.5Fe68Co10</sub<B7 or HP2=Nd14Dy1Fe68Co10B7) and soft phase Fe, prepared by sputtering and subsequent heat treatment, have been investigated. For Si/Ti(20 nm)/[HP1(2.0 nm)/Fe(0.5 nm)] x 200/Ti(10 nm) multilayer film, transmission electron microscopy results show that Fe disperses in amorphous NdDyFeCoB alloy. After annealing at 575 °C for 5 min, the hard Nd2Fe14B phase typically with grains of about 50 nm and some amount of α-Fe coexist in the film. The grain size of the hard and soft phases can be controlled by the proper thickness of the layer and the period. A coercivity of 7.7 kOe and a ratio Mr/Ms of 0.74 are achieved in the multilayer Si/Ti(20 nm) /[HP2(2 nm) /Fe(0.5 nm)]x200/Ti(10 nm). A good squareness of the hysteresis loop (measured even at 200 K) is observed, due to the effective exchange coupling between the magnetically soft and hard nanograins in the film. A pinning-type mechanism dominates the magnetization reversal process. In addition, the effect of the effective anisotropy, the grain size, and interfaces between the magnetically hard and soft phases on the exchange coupling is discussed. W. Liu