Effect of the 16O → 18O isotopic substitution and a magnetic field on the spin dynamics in the (La0.25Pr0.75)0.7Ca0.3MnO3 manganite according to the 139La NMR data |
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Authors: | K N Mikhalev I E Litvinov Z N Nigamatyanova A Yu Yakubovskii A R Kaul O Yu Gorbenko K Kumagai and Y Furukawa |
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Institution: | (1) Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. Sof’i Kovalevskoi 18, Yekaterinburg, 620041, Russia;(2) Russian Research Centre Kurchatov Institute, pl. Akademika Kurchatova 1, Moscow, 123182, Russia;(3) Moscow State University, Leninskie gory, Moscow, 119992, Russia;(4) Hokkaido University, Sapporo 060-0810, Japan |
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Abstract: | 139La nuclear magnetic resonance spectra have been recorded and the spin-spin relaxation times in the paramagnetic region in
external magnetic fields of 5 and 9.4 T have been measured for two types of manganites: initial (La0.25Pr0.75)0.7Ca0.3Mn16O3 and enriched with the 18O isotope ((La0.25Pr0.75)0.7Ca0.3Mn18O3). The manganite enriched with the heavier oxygen isotope exhibits disappearance of a signal in the charge-ordering region
(T < T
co) in an external field of 5 T. This effect is related to the anomalous increase in the spin-spin relaxation rate. With an
increase in the external magnetic field to 9.4 T, the difference in the behavior of the relaxation rate for the two samples
in the charge-ordering region remains pronounced, although the magnitude of this effect becomes much smaller. The observed
giant isotope effect is a bright evidence of the important role of oxygen motion in the formation of long-range magnetic order
in the manganites under consideration.
Original Russian Text ? K.N. Mikhalev, I.E. Litvinov, Z.N. Nigamat’yanova, A.Yu. Yakubovskii, A.R. Kaul’, O.Yu. Gorbenko,
K. Kumagai, Y. Furukawa, 2007, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 5,
pp. 726–729. |
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