A silica supported Ni catalyst has been investigated by electron magnetic resonance between 293 and 4.2 K. A relatively narrow absorption signal with linewidth Dgr;Hppquest;400 Oe is observed at temperatures quest;150 K as a result of motional averaging of the magnetocrystalline anistropy fieldHaof the Ni particles resulting from superparamagnetism. Broadening of the resonance occurs at lower temperatures because of a reduction of the influence of thermal fluctuations. A line shape analysis of the observed resonance signals is carried out employing the theory of ferromagnetic resonance in polycrystalline material. The calculated anisotropy field is reduced in the particles as compared to bulk Ni. The Landaundash;Lifshitz relaxation frequency obtained from the calculated rsquo;rsquo;single crystalrsquo;rsquo; linewidths are found to be larger than those of bulk Ni single crystals. Concurrently with line broadening, the resonance shifts to lower magnetic fields. The resonance shifts are approximatelyHa/2. The appearance of magnetoelastic effects in the resonance below 120 K indicates the presence of small but significant strain in the particles resulting from particlehyphen;support interaction.
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