Spin-lattice relaxation of Co(II) in hexaaquocobalt(II) picrylsulphonate tetrahydrate: An estimate from EPR line width of the dopant, Mn(II)

Single crystal EPR of Mn(II)-doped [Co(H2O)(6)] (picsul)(2) . 4H(2)O is stu died in the temperature range of 123-300 K. The angular variation of the ze ro-field transitions, observed from a single magnetically distinct site, is successfully simulated with an asymmetric zero-held tensor with D = 436 x 10(-4) cm(-1) and E = 79 x 10(-4) cm(-1). Sharp EPR spectra observed for Mn (II), a paramagnetic dopant in the paramagnetic host lattice, are attribute d to host-spin-lattice relaxation narrowing. Based on the theory of exchang e narrowing of dipolar coupling, the T-1 of Co(II) has been estimated to be 0.54 x 10(-12) s at 300 K. From the temperature dependence of T-1, it is p ostulated that two-phonon Raman process is the dominant mechanism for spin- lattice relaxation above 250 K, and below 250 K a cross-relaxation process is evident. (C) 1999 Elsevier Science B.V. All rights reserved.