Exchange Interactions between Dissimilar JT Copper Ions in K2Zn0.92Cu0.08(SO4)2 � 6D2O and (ND4)2Mg0.92Cu0.08(SO4)2 � 6D2O Crystals

Abstract

A study of exchange and vibronic interactions in pairs of dissimilar (D-S) Jahn-Teller ions in Cu 2þ doped zinc potassium (I) and magnesium ammonium (II) Tutton salts is reported. An interpretation of EPR spectra is done on the basis of the predicted differences in the angular dependences of resonance lines originating from isolated centres and pairs of similar and dissimilar ions. An assignment of D-S pairs is confirmed by the so-called reverse shift manifested as non-coincidence of the centres of pair spectra with those of appropriate isolated ion spectra. It is shown that for the spin-spin interaction parameter K < (g 1z À g 2z ) bB (K is the sum of isotropic (J) and anisotropic (D) contributions) the reverse shift is always present in the spectrum of exchange pairs of D-S ions. The g z values for such pairs are determined by g z pair ¼ g 1; 2z AE 1 4 ðg 1z À g 2z Þ D 2 2 , where D 2 ¼ ðK xx þ K yy Þ=½2ðg 1z À g 2z Þ bB. The reverse shift for the compounds studied takes values of 0.6-1.0 mT. The values of J (I) ¼ 0.0034 cm --1 ; D (I) ¼ 0.0072 cm --1 for the potassium and J (II) ¼ 0.009 cm --1 ; D (II) ¼ 0.0068 cm --1 for the ammonium compounds are determined. A possible existence of vibronic correlation is discussed.