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spp1997新虫 (初入文坛)
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[求助]
求翻译，英译中
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In glass technology crystallization must usually be avoided; however, partially crystallized glasses or ‘glass-ceramics’, containing fine crystallized particles (nanoparticles), have been developed for specific applications. These nanoparticles confer particular characteristics to glasses, such as strength and impact resistance, lower thermal expansion coefficient, partial or complete opacity, etc [1]. A special type of nanoparticles, ferro- or ferrimagnetically ordered crystalline nanoparticles imbedded in different diamagnetic matrices such as fluids or polymers, gives rise to a new kind of magnetism called superparamagnetism and results in a number of properties which are interesting from a technical viewpoint, for example see [2]. Partially crystallized glasses containing ferromagnetic nanoparticles constitute a novel and much more complex class of superparamagnetic materials. Their properties are mainly determined by morphology (size and shape distributions) and magnetic constants of such particles. Electron magnetic resonance, sensitive to both the magnetic constants and the structure of the environment of a magnetic ion, is well adapted to the study of superparamagnetic nanoparticles [3]. In this case it may be called superparamagnetic resonance (SPR) to distinguish it from the resonance of individual electron spins usually referred to as electron paramagnetic resonance (EPR). Up until now, only a few attempts have been made to carry out quantitative, computer-simulation based analysis of SPR spectra of magnetic particles dispersed in polycrystalline or glassy systems [3–5]. In a previous work [3] we have dealt with transformations arising in the electron magnetic resonance spectra of borate glasses containing small amounts of iron oxide after heat treatment above the glass transition temperature. Namely, the resonance characteristic of diluted Fe3+ ions in the glass, observed at the effective g-value gef = 4.3 [6], progressively disappears and a new resonance, consisting of superposed broader and narrower components, grows at gef ≈ 2.0. This compound resonance signal has been ascribed to a superparamagnetic assembly of crystalline ferromagnetic single-domain particles arising in the diamagnetic glassy matrix under heat treatment. Good computer fits to this resonance have been obtained assuming a monodisperse distribution of the particle sizes. This paper presents a more detailed analysis of room temperature X-band SPR spectra obtained after repeated annealing steps of iron-doped borate glass. First, data are reported on the evolution of the number of spins with annealing, as obtained from resonance intensity measurements. Then, geometrical characteristics of the magnetic particles obtained from a series of computer simulations of the spectra are related to the anneal temperature. Finally, the mechanism of growth of crystallized magnetic particles is discussed. |
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