μ+ SR studies on pure MnF2 and site-diluted (Mn0.5Zn0.5)F2SR studies on pure MnF2 and site-diluted (Mn0.5Zn0.5)F2 |
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| Authors: | Y J Uemura R Keitel M Senba R F Kiefl S R Kreitzman D R Noakes J H Brewer D R Harshman E J Ansaldo K M Crowe A M Portis V Jaccarino |
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| Institution: | (1) Brookhaven National Lab., 11973 Upton, New York, USA;(2) TRIUMF, V6T-2A3 Vancouver, B.C., Canada;(3) Dept. of Physics, Univ. of Saskatchewan, S7N-OWO Saskatoon, Saskatchewan, Canada;(4) Dept. of Physics, Univ. of California, 94720 Berkeley, California, USA;(5) Dept. of Physics, Univ. of California, 93106 Santa Barbara, California, USA |
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| Abstract: | Positive muon spin rotation and relaxation measurements have been carried out on the antiferromagnets, pure MnF2 and site-diluted (Mn0.5Zn0.5)F2, above and below the Néel temperature TN using single-crystal specimens. Two different muon signals have been found in the pure MnF2; with the precession frequency υA for the site A and υB for the site B measured in zero external magnetic field at T=5 K. We propose a picture that the signal from the A site represents
the “muonium” state, and discuss the characteristic features of muonium in magnetic materials. The spin relaxation rate 1/T1, measured in zero external field, decreases rapidly with decreasing temperature below TN. The mechanism of the spin relaxation above TN is explained by the exchange fluctuations of the Mn moments, while below TN by the Raman scattering of spin waves. At the same normalized temperature T/TN, 1/T1 observed in the diluted (Mn0.5Zn0.5)F2 is significantly larger than that in the pure MnF2 below TN. The difference between the pure and diluted systems is related to the large spectral weight of low-energy magnons in (Mn0.5Zn0.5)F2 found by neutron scattering. |
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