Contains papers presented as part of the 1991 Spring Meeting of the Materials Research Society.

Proceedings of the NATO Advanced Research Workshop on Ferrimagnetic Nano-crystalline and Thin Film Magnetooptical and Microwave Materials, Sozopol, Bulgaria, 27 September - 3 October, 1998

Issues in General Physics Research / 2011 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about General Physics Research. The editors have built Issues in General Physics Research: 2011 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about General Physics Research in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Issues in General Physics Research: 2011 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.

Aimed primarily at experimental chemists, physicists, electronic engineers and material scientists interested in particulate and granular magnetic materials, this textbook is the culmination of over 40 years' research into the subject. The text is divided into two parts. Part One covers the basic physics of magnetism from a relatively low level, including an explanation of some of the unusual terminology in magnetism such as the idea of poles and flux, whose origins are little understood. The complexity of the unit systems in magnetism are also presented. Thereafter a brief review of the principles of domain theory is presented and thermal activation effects and their correct measurement are discussed in some detail. The topic of exchange bias, where an antiferromagnetic material is grown in intimate contact with a ferromagnet, is presented in significant detail reviewing old theories and numerical models but then focusing on what has become known as the York Model of Exchange Bias which is now universally accepted as the model which describes the behaviour of exchange bias systems when grown in the form of granular thin films. In Part Two a detailed description of ferrofluids is presented including a simple method for their preparation and the various engineering applications in vacuum seals, loudspeakers, sink float separation and the alignment of non-magnetic entities.A description is provided of the phenomenon of magnetic hyperthermia which is a developing technology with significant potential applications in medicinal therapies. Other applications of magnetic nanoparticles in biomedicine are also presented. An extensive discussion of magnetic information storage in conventional recording systems is described, including the brief history of the development of this technology whose scale is now enormous as most of the cloud computing systems in current use are based on hard drive technology.

Nanofabrication of magnetic media with large magnetocrystalline anisotropy has become a very important topic as technological demands continue to increase. These demands include ever rising requirements of areal density in magnetic storage media such as hard disk drives (HDD), as well as searches for rare-earth-free permanent magnets to meet future clean energy technology. Certain L10-ordered materials, a chemically ordered, face-centered tetragonal structure, possess highly desirable magnetic properties which have been the focus of intense research over the past decade. These magnetic properties include a large magnetic anisotropy, a moderate Curie temperature, and a large saturation magnetization. On the other hand, these materials suffer from significant drawbacks in the deployment for technological applications, particularly due to the difficulty in realizing the L10 phase. Understanding the physical interactions in prototype technological systems utilizing L10 materials and quantifying their limitations is key to formulating a research and development path forward. As such, this line of research attempts to address important scientific and technological challenges in such high anisotropy materials. In future HDD technology granular L10-ordered materials are promising media candidates that can achieve even higher areal densities. This is of prime importance because the thermal stability of magnetic bits is compromised as each bit becomes even smaller. One method to combat this is the use of a magnetic material with a very high magnetocrystalline anisotropy, which, in turn, increases the necessary switching field. Creating a thermally stable magnetic grain that can be recorded under a finite write field will be accomplished with the emerging heat-assisted magnetic recording technology. While much work has been done on L10-ordered magnetic media, there is still great deal to be studied in using them as potential HAMR media. In this thesis, a comprehensive set of high temperature magnetic studies, as well as structural characterizations, were carried out on high anisotropy FePt and FeNi alloys in the L10 phase. The first order reversal curve (FORC) technique is applied extensively to identify reversal mechanisms and distinguish different phases within the material, and quantify their behavior and interactions. The effects of segregant combinations in laminated FePt-based granular media were investigated. These structures can be tailored by the additional co-sputtering of segregants alongside magnetic material in various layering schemes to tune properties such as chemical ordering, magnetic anisotropy, grain morphology, magnetic switching fields and switching field distributions, and thermal stability. Magnetic media were grown with three distinct segregant profiles: a single media with spherical grains, dual layer media with columnar grains, and triple layer media with Voronoi grains. FORC analysis shows that increasing the number of layers with alternating segregant composition not only improves the grain shape geometry, but also better retains the L10 ordering throughout the heating cycle. Continuing the study of granular FePt-based media, layered stacks of FePt media were exposed to varying amounts of light-ion irradiation using helium. L10-ordered media suffers from the high temperatures required to reach a high degree of chemical ordering. Three films were created using a FePt-(C,BN) dual layer system, and two were exposed to light-ion irradiation at varying annealing temperatures to promote greater chemical ordering with increased atomic mobility. An increase in chemical ordering was found after annealing at 500 °C, vs. a decrease found after annealing at 400 °C, compared to an unirradiated sample. The coercivity distribution, peak coercivity, and hard L10 phase fraction were found to be enhanced after irradiation and annealing at 500 °C. Finally, rapid thermal annealing with extreme speeds was employed to induce L10 ordering in FeNi thin films. Magnetic properties were examined using the FORC technique, and structural characterizations were done with transmission electron microscopy and electron diffraction. After rapid thermal annealing the samples exhibit almost two-orders of magnitude increase in coercivity, along with the appearance of forbidden electron diffraction peaks, confirming the realization of L10 ordered high anisotropy FeNi. These results demonstrate an effective route to achieve high anisotropy rare-earth-free magnets using earth-abundant elements.

Please note this is a Short Discount publication. This, the third report in Elsevier's Materials Technology in Japan series, concentrates on magnetic materials as a topic gaining worldwide attention, and each chapter looks not only at current research, but also describes the technology as it is being applied and its future potential. Magnetic–related research is the second largest field of research in Japan after semiconductors, with the estimated number of researchers and engineers engaged in magnetics–related activities currently at 20,000. This research report serves as both a review of research undertaken and developments to date, and a forecast of where the industry is going.

MAX phases are a group of nanolaminated ternary carbides and nitrides, with a composition expressed by the general formula Mn+1AXn (?? = 1 ? 3), where M is a transition metal, A is an A-group element, and X is carbon and/or nitrogen. MAX phases have attracted interest due to their unique combination of metallic and ceramic properties, related to their inherently laminated structure of a transition metal carbide (Mn+1Xn) layer interleaved by an A-group metal layer. This Thesis explores synthesis and characterization of magnetic MAX phases, where the A-group element is gallium (Ga). Due to the low melting point of Ga (T = 30 °C), conventional thin film synthesis methods become challenging, as the material is in liquid form at typical process temperatures. Development of existing methods has therefore been investigated, for reliable/reproducible synthesis routes, including sputtering from a liquid target, and resulting high quality material. Routes for minimizing trial-and-error procedures during optimization of thin film synthesis have also been studied, allowing faster identification of optimal deposition conditions and a simplified transfer of essential deposition parameters between different deposition systems. A large part of this Thesis is devoted towards synthesis of MAX phase thin films in the Cr-Mn-Ga-C system. First, through process development, thin films of Cr2GaC were deposited by magnetron sputtering. The films were epitaxial, however with small amount of impurity phase Cr3Ga, as confirmed by X-ray diffraction (XRD) measurements. The film structure was confirmed by scanning transmission electron microscopy (STEM) and the composition by energy dispersive X-ray spectroscopy (EDX) inside the TEM. Inspired by predictive ab initio calculations, the new MAX phase Mn2GaC was successfully synthesized in thin film form by magnetron sputtering. Structural parameters and magnetic properties were analysed. The material was found to have two magnetic transitions in the temperature range 3 K to 750 K, with a first order transition at around 214 K, going from non-collinear antiferromagnetic state at lower temperature to an antiferromagnetic state at higher temperature. The Neél temperature was determined to be 507 K, changing from an antiferromagnetic to a paramagnetic state. Above 800 K, Mn2GaC decomposes. Furthermore, magnetostrictive, magnetoresistive and magnetocaloric properties of the material were iv determined, among which a drastic change in lattice parameters upon the first magnetic transition was observed. This may be of interest for magnetocaloric applications. Synthesis of both Cr2GaC and Mn2GaC in thin film form opens the possibility to tune the magnetic properties through a solid solution on the transition metal site, by alloying the aforementioned Cr2GaC with Mn, realizing (Cr1-xMnx)2GaC. From a compound target with a Cr:Mn ratio of 1:1, thin films of (Cr0.5Mn0.5)2GaC were synthesized, confirmed by TEM-EDX. Optimized structure was obtained by deposition on MgO substrates at a deposition temperature of 600 ºC. The thin films were phase pure and of high structural quality, allowing magnetic measurements. Using vibrating sample magnetometry (VSM), it was found that (Cr0.5Mn0.5)2GaC has a ferromagnetic component in the temperature range from 30 K to 300 K, with the measured magnetic moment at high field decreasing by increasing temperature. The remanent moment and coercive field is small, 0.036 ?B, and 12 mT at 30 K, respectively. Using ferromagnetic resonance spectroscopy, it was also found that the material has pure spin magnetism, as indicated by the determined spectroscopic splitting factor g = 2.00 and a negligible magnetocrystalline anisotropy energy. Fuelled by the recent discoveries of in-plane chemically ordered quaternary MAX phases, so called i-MAX phases, and guided by ab initio calculations, new members within this family, based on Cr and Mn, were synthesized by pressureless sintering methods, realizing (Cr2/3Sc1/3)2GaC and (Mn2/3Sc1/3)2GaC. Their structural properties were determined. Through these phases, the Mn content is the highest obtained in a bulk MAX phase to date. This work has further developed synthesis processes for sputtering from liquid material, for an optimized route to achieve thin films of controlled composition and a high structural quality. Furthermore, through this work, Mn has been added as a new element in the family of MAX phase elements. It has also been shown, that alloying with different content of Mn gives rise to varying magnetic properties in MAX phases. As a result of this Thesis, it is expected that the MAX phase family can be further expanded, with more members of new compositions and new properties.