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|Type:||Artigo de periódico|
|Title:||Phase Transition In Metal Hexammine Complexes. Ii. The Epr Spectra Of Ni(no3)26nh3 And Ni++ Doped Zn(no3)26nh3 And Cd(no3) 26nh3|
|Abstract:||The cooperative effect of the ammonias in X(NO3) 26NH3 (X=Ni,Zn,Cd) was investigated by EPR. In Ni(NO 3)26NH3, the linewidth of the single EPR absorption line undergoes a sudden broadening at Tc=243 K. This effect is probably a result of a cooperative freezing of the degrees of freedom of rotation of the ammonias, giving the appearance of a crystal field on the Ni++ ions. The crystal field does not split the single line, probably because strong exchange effects assemble the lines. The crystal field parameter D=0.425 cm-1 was evaluated by applying the Anderson and Weiss theory for the exchange narrowing of the linewidth. Small quantities of the Ni ++ ions in Zn and Cd salts do not exhibit strong exchange effects. So the single EPR absorption line above Tc goes to a split line below Tc. For Ni:Zn(NO3)26NH3, T c=231 K and D=0.606 cm-1. For Ni:Cd(NO3) 26NH3, Tc=198 K and D≃0.3 cm-1. Hysteresis in Tc was also observed for all salts. Copyright © 1975 American Institute of Physics.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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