Proton Nuclear Magnetic Resonance Studies in KH2PO4, KH2AsO4, NH4H2PO4, and NH4H2AsO4

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Abstract
Studies have been made of the proton magnetic resonance absorption at 30 Mc/sec. in KH2PO4, KH2AsO4, NH4H2PO4, and NH4H2AsO4. Both line shapes and relaxation times have been measured from 87°K to 293°K. The potassium salts show closely similar magnetic resonance properties. Their relaxation times show relatively small variation in the temperature interval studied. The characteristic times derived therefrom do not obey any simple exponential law in the reciprocal temperature. Single crystals of KH2PO4 do not seem to show anisotropy in the relaxation time. A formula is given which relates the anisotropy of the motion of magnetic dipoles to the anisotropy of transverse local field variation. The ammonium salts show two minima in their relaxation time vs. temperature curves. One minimum corresponds to a temperature at which the acid hydrogens are the most effective relaxation agent and the other to a temperature where the ammonium ion hydrogens are most effective. The line shapes are also of a composite character. This is most clearly shown below 100°K where the absorption lines appear to be super-positions of the broad NH4 line for which that of NH4Cl is typical and the narrow line found in KH2PO4 or KH2AsO4. Possible interpretations of the experimental results are discussed with reference to the motions of the protons in these crystals.