Two kinds of motions of proton in dimeric carboxyl group were distinguished by the temperature dependence of spin-lattice relaxation times of dipolar system (T1d) and of Zeeman system (T1z) on acethylenedicarboxylic acid (ADCA) and on p-nitrobenzoic acid (PNBA) in the A2⁄a form. High temperature motion of ADCA is 180° rotation of the eight-membered ring of dimeric carboxyl group about the axis nearly parallel to the hydrogen bonds. The activation energy of this motion of ADCA is 58 kJ mol−1. The low temperature motion of ADCA and PNBA is the proton translation along the hydrogen bonds in a dimeric carboxyl group, which induces the minima of T1z and T1d at the same temperature. The activation energy derived from the high temperature slope of T1z curve is 6.9 kJ mol−1 for ADCA and 2.5 kJ mol−1 for PNBA. The low temperature slope gives a small activation energy of 1.9 kJ mol−1 for ADCA and 1.0 kJ mol−1 for PNBA. The frequency dependence of T1z in the low temperature limit was constant at low Larmor frequency. This result indicates that the translational motion of protons along the hydrogen bonds is not classical but quantum-mechanical.
This paper describes a novel type of high electrical resistance composite magnet. They were made by compacting or consolidating Sm-Fe-N powders coated with a continuous ferrite layer, which suppresses intergrain conductivity but sustains magnetic exchange interactions among grains. Sm-Fe-N powders ͑2 m in size͒ were coated with an "iron ferrite" ͑an intermediate between magnetite and maghemite͒ layer by ferrite plating, an aqueous process. They were compacted at 100 MPa to form a ferrite/SmFeN composite magnet ͑note that row Sm-Fe-N powders cannot be consolidated strongly enough to form magnets͒, and then consolidated to 92-94 vol % by the explosive consolidation technique. Coercivity and rectangularity of the compacting composite magnet decreased slightl by 2.0% and 1.4%, respectively, when compared to those of Sm-Fe-N powder compact. We also estimated the resistivity of fully dense ferrite/Sm-Fe-N magnet to be about 4000 ⍀ cm, ten times higher than the estimated value of a fully dense Sm-Fe-N magnet. Thus, the ferrite layer in our composite magnet retains magnetic exchange coupling among Sm-Fe-N grains, and yet suppresses intergrain electrical coupling to increase resistivity. This will decrease eddy current loss and improve high frequency characteristics of composite magnets.
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