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The mapon technique and recent developments
Authors:P J Back
Institution:(1) Clarendon Laboratory, Parks Road, Oxford, U.K.
Abstract:Typical linewidths observed in NMRON on dilute impurities in ferromagnetic metals are of order 1 MHz, making difficult the observation of structure in the resonance with splitting Δv much less than this value. The technique of Modulated Adiabatic Passage on Oriented Nuclei (MAPON) was recently developed as a means of measuring the weak electric quadrupole splitting ΔvQ of the nuclear hyperfine interaction due to an electric field gradient Vzz. MAPON has successfully been applied to measure ΔvQ as low as 4 kHz, i.e. less than 0.5% of the inhomogeneously broadened NMRON CWFM resonance line. The isotopes56Co,57Co,58Co and60Co have been studied in iron single crystal hosts, yielding ΔvQ consistent with known and estimated quadrupole moments. In addition the results to date give striking confirmation of analyses based on the single impurity relaxation model. Following a brief summary of the theoretical development of MAPON a review of experimental data is given for the CoFe<100> system. The variation of ΔvQ with direction of magnetization, measured in58CoFe and60CoFe single crystal samples, is also described. Further MAPON measurements are described for a56CoFe polycrystalline sample, for which the most probable value and width of the distribution of Vzz can be described simply in terms of the single crystal principal axis results. The application of the MAPON technique to the measurement of nuclear electric quadrupole moments in implanted and diffused samples is discussed.
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