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Cross relaxation studies in the Cr 3+ ‐doped magnetically dilute paramagnetic Al 2 O 3 –Fe 2 O 3 system. I. Effect of Cr 3+ concentration
Author(s) -
Srivastava J. K.,
Dale B. W.
Publication year - 1978
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.2220900144
Subject(s) - hyperfine structure , paramagnetism , diamagnetism , ion , relaxation (psychology) , analytical chemistry (journal) , doping , spins , chemistry , materials science , crystallography , nuclear magnetic resonance , atomic physics , condensed matter physics , magnetic field , physics , psychology , social psychology , optoelectronics , organic chemistry , quantum mechanics , chromatography
Mössbauer measurements are made in undoped and Cr 3+ ‐doped Al 2 O 3 –0.04 mol% 57 Fe 2 O 3 systems at 4.2 K. The cross relaxation between Fe 3+ and Cr 3+ ions, dispersed in the diamagnetic Al 2 O 3 lattice, is studied. The spin–spin relaxation time of the Cr 3+ ions is reduced with increasing Cr 3+ concentration and these faster relaxing Cr 3+ spins are found to enhance the Fe 3+ ‐relaxation process, destroying the paramagnetic hyperfine structure observed in the 57 Fe Mössbauer spectra of undoped Al 2 O 3 –0.04 mol% 57 Fe 2 O 3 . It is concluded that at higher Cr 3+ concentrations, cross relaxation does not take place by the mutual energy exchange between a Cr 3+ ion and and Fe 3+ ion but a new kind of pair cross‐relaxation process occurs where a Cr 3+ ion and an Fe 3+ ion first form an exchange coupled pair and then two such pairs cross relax.