APPLICATIONS OF THE MÖSSBAUER SPECTROSCOPY

1. APPLICATIONS OF THE MÖSSBAUER SPECTROSCOPY G. Spina INFM Firenze, Dip. Fisica Università di Firenze. E-mail: gabriele.spina@unifi.it L. Cianchi, F. Del Giallo, M. Lantieri, P. Moretti IFAC CNR, Sez. Struttura della Materia e Spettroscopia E-mail: l.cianchi@ifac.cnr.it Hyperfine transitions 57Fe Mössbauer spectra The figure shows typical spectra of the 57Fe subject to static hyperfine fields. In the magnetic case, the field is usually time depending, due to spin fluctuations. Frequencies in the 106-1012 s-1 range can be obtained from the spectrum fits. As the frequency increases, the hyperfine structure tends to disappear more and more. The relaxation spectra are then obtained (see the figure at the right side). Magneticdipole Mössbauer spectra of iron oxides embedded as small grains in a pink marble. Contributions of different oxidation states of the iron are separately shown. Moreover, different grain sizes give different relaxation spectra of the Fe3+ ions. Electric quadrupole Isomer+ SOD shift The Lamb-Mössbauer f-factor (fraction of g-photons recoilless emitted ) can be obtained from the absorption area A of the spectrum. In its turn, the mean square displacement (MSD) of the emitting nucleus in the g-ray direction is given by: <x2> = -(l2/ 4p2) ln(f), where l is the photon wave-length. Example of Fe(III) cluster (Fe4). The ion spins in the ground state are shown. Fe4 Mössbauer spectra between 1.38 and 77 K were collected which show evident relaxation effects. The 1.32 K spectrum displays a well-resolved hyperfine structure, since only the ground state (for which the spin fluctuations are negligible) is populated. The trend versus T of the mean frequency of the spin fluctuations is: In the figure the MSD trends of the 151Eu in the cuprate EuSr2Cu3O7 (red) and in the superconducting counterpart EuBa2Cu3O7 (violet) are reported as functions of the temperature. -1 = 0-1 exp(-/T) where 0-1 = 2 107+1012 exp(-136/T) (s-1)  magnetic anisotropo barrier  7 K