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m/sup +/SR studies on pure MnF/sub 2/ and site-diluted (Mn/sub 0. 5/Zn/sub 0. 5/)F/sub 2/

Description: Positive muon spin rotation and relaxation measurements have been carried out on the antiferromagnets, pure MnF/sub 2/ and site-diluted (Mn/sub 0.5/Zn/sub 0.5/)F/sub 2/, above and below the Neel temperature T/sub N/ using single-crystal specimens. Two different muon signals have been found in the pure MnF/sub 2/; with the precession frequency nu/sub A/ = 1.3 GHz for the site A and nu/sub B/ = 152 MHz 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/T/sub 1/, measured in zero external field, decreases rapidly with decreasing temperature below T/sub N/. The mechanism of the spin relaxation above T/sub N/ is explained by the exchange fluctuations of the Mn moments, while below T/sub N/ by the Raman scattering of spin waves. At the same normalized temperature T/T/sub N/, 1/T/sub 1/ observed in the diluted (Mn/sub 0.5/Zn/sub 0.5/)F/sub 2/ is significantly larger than that in the pure MnF/sub 2/ below T/sub N/. The difference between the pure and diluted systems is related to the large spectral weight of low-energy magnons in (Mn/sub 0.5/Zn/sub 0.5/)F/sub 2/ found by neutron scattering.
Date: January 1, 1986
Creator: Uemura, Y.J.; Keitel, R.; Senba, M.; Kiefl, R.F.; Kreitzman, S.R.; Noakes, D.R. et al.
Partner: UNT Libraries Government Documents Department

Determination of very slow. mu. /sup +/ hop rates in Cu by LLF-. mu. SR

Description: Muon spin relaxation in low (weak) longitudinal magnetic field (LLF-..mu..SR) provides a means of independently determining the static dipolar width ..delta.. characterizing the ..mu../sup +/ lattice site and the correlation time tau/sub c/ for ..mu../sup +/ hopping, in a manner that is nearly model-independent for tau/sub c/ and especially accurate in the near-static limit (tau/sub c/ > tau/sub ..mu../). The advantages of this method are illustrated by its application to muon hopping in Cu near the tau/sub c/ maximum around 50/sup 0/K.
Date: January 1, 1986
Creator: Brewer, J.H.; Celio, M.; Harshman, D.R.; Keitel, R.; Kreitzman, S.R.; Luke, G.M. et al.
Partner: UNT Libraries Government Documents Department

mu. /sup +/SR in amorphous spin glasses Pd/sub 75/Fe/sub 5/Si/sub 20/ and Pd/sub 75/Fe/sub 5/P/sub 5/

Description: The zero-field muon spin relaxation function G/sub zz/(t) has been measured as a function of reduced temperature t = T/T/sug g/ in the amorphous metallic spin glasses Pd/sub 75/Fe/sub 5/Si/sub 20/ and Pd/sub 75/Fe/sub 5/P/sub 20/. The results are in qualitative agreement with earlier measurements on dilute alloy spin glasses, including an onset of static order below T/sub g/ and a (t/(t - 1))/sup 2/ dependence of the correlation time tau/sub c/ above T/sub g/. Both samples have the same tau/sub c/(t) above T/sub g/ and almost identical static width ..delta../sub s/ ..-->.. ..delta../sub 0/ approx. = 43 ..mu..s/sup -1/) as T ..-->.. 0, but the t-dependence of ..delta../sub s/ near T/sub g/ differs markedly.
Date: January 1, 1986
Creator: Brewer, J.H.; Spencer, D.P.; Huang, C.Y.; Uemura, Y.J. & Chen, H.S.
Partner: UNT Libraries Government Documents Department

Muon spin relaxation in CeCu/sub 2/Si/sub 2/ and muon Knight shift in various heavy-fermion systems

Description: Positive muon spin precession has been observed in varius heavy-fermion systems in the transverse external magnetic field. In the superconductor CeCu/sub 2.1/Si/sub 2/, the relaxation rate of muon spins increases rapidly with decreasing temperature below T/sub c/. This is interpreted as the results of the inhomogeneous fields due to the imperfect penetration of the external field into the type-II superconducting state. The magnetic-field penetration depth lambda is derived from the observed muon spin relaxation rate. lambda is about 1200 A at T approx. 0.5T/sub c/, and the temperature dependence of lambda is consistent with the relation expected for a BCS superconductor. We have also measured the muon Knight shift K/sub ..mu../ in the normal (or paramagnetic) state of various heavy-fermion systems. K/sub ..mu../ is large and negative (about -1000 approx. -3000 ppM at T = 10 K) for CeCu/sub 2/Si/sub 2/, UPt/sub 3/ and CeAl/sub 3/, while more complicated signals are measured in CePb/sub 3/ and CeB/sub 6/. The negative muon Knight shift in the non-magnetic heavy-fermion systems is discussed in terms of the Kondo-coupling between the conduction- and f-electrons.
Date: January 1, 1986
Creator: Uemura, Y.J.; Kossler, W.J.; Hitti, B.; Kempton, J.R.; Schone, H.E.; Yu, X.H. et al.
Partner: UNT Libraries Government Documents Department

Comparison between muon spin rotation and neutron scattering studies on the 3-dimensional magnetic ordering of La/sub 2/CuO/sub 4-y/

Description: Muon spin rotation and neutron scattering studies on powder and single-crystal specimens of La/sub 2/CuO/sub 4-v/ are compared. The apparent difference between the muon and neutron results for the ordered moment in the antiferromagnetic state is interpreted as the signature of increasingly short-ranged spatial spin correlations with increasing oxygen content.
Date: January 1, 1988
Creator: Uemura, Y.J.; Kossler, W.J.; Kempton, J.R.; Yu, X.H.; Schone, H.E.; Opie, D. et al.
Partner: UNT Libraries Government Documents Department