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Study of the [Fe(OMe)(dpm)2]2 dimer in the presence of a magnetic field by using Mössbauer spectroscopy (Contributo in atti di convegno)

Type

Contributo in atti di convegno (Classe)
Prodotto della ricerca (Classe)

Label

Study of the [Fe(OMe)(dpm)2]2 dimer in the presence of a magnetic field by using Mössbauer spectroscopy (Contributo in atti di convegno) (literal)

Anno

2005-01-01T00:00:00+01:00 (literal)

Alternative label

Cianchi L., Del Giallo F., Lantieri M., Moretti P., Spina G. (2005)
Study of the [Fe(OMe)(dpm)2]2 dimer in the presence of a magnetic field by using Mössbauer spectroscopy
in ICAME 2005, Montpellier, France
(literal)

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Cianchi L., Del Giallo F., Lantieri M., Moretti P., Spina G. (literal)

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Reprinted from Hyperfine Interactions 2006. (literal)

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Proceedings of the 28th International Conference on the Applications of the Mössbauer Effect, held in Montpellier, France, 49 September 2005, P.-E. Lippens, J.-C. Jumas and J.-M. R. Génin (eds)., II(Part IIIV/V), Part 67, 1115-1119 (2007). Reprinted from Hyperfine Interactions 2006. Springer (literal)

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In the [Fe(OMe)(dpm)2]2 cluster (Fig.1), the two Fe(III) ion spins (s=5/2) are antiferromagnetically coupled via oxomethil bridges, so that its spin can assume six possible values from 0 to 5 in order of increasing energy. In a previous paper a Mössbauer study of the spin dynamics between 6.5 and 288 K in the absence of an external magnetic field was performed on the basis of fast relaxation limit. Although for T < 40 K spectra are not suitable to evaluate the relaxation rate, in the range from 60 to 200 K a quasi-flat trend of this parameter was found. Similar behaviours had been already observed in other S=0 ground state ring-shaped iron clusters (i.e. Fe6 [2]). In the present work we will study the same dimer in the presence of a 5 T longitudinal magnetic field in the temperature range from 7.6 to 33 K. From the fitting of these spectra the isomer shift (IS), the two independent EFG components (Q, ·) and the direction and intensity of the magnetic anisotropy can be evaluated. Moreover, by assuming a spin-thermal bath interaction described by the Hamiltonian H=F Sx, where F is a stochastic real function the value of which gives the interaction intensity and Sx denotes the spin x-component, we are able to estimate the Fourier Transform at zero frequency (J) of the correlation function of F just in that range where the fitting in the absence of magnetic field failed. By assuming an anisotropy component in the exchange interaction that couples the singlet S=0 with the triplet S=1, we are able to obtain fairly good fittings (Fig.2). From a preliminary analysis of the spectra it follows that IS = 0.41 mms-1, Q = 0.38 mms-1 and · >>1, considering the z axis to be coincident with the Fe(III)-Fe(III) direction. As far as the magnetic anisotropy is concerned, its axis results to be perpendicular to the zaxis and its value of the order of 10 K. Finally, a value of order 10^7 s-1 is obtained for J. (literal)

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