The paramagnetic dispersion phenomena in Co(HCOO) 2 2H 2 O in the ordered state are studied. The phenomena can not be attributed to the cross relaxation among Co 2+ and impurity Ni 2+ ions. It is accounted for as cross relaxations among dissimilar paramagnetic Co 2+ ions located between antiferromagnetic sheets. The exchange interaction J A B between antiferromagnetic ion and its adjacent paramagnetic ion is determined as J A B / k =0.60 K by the observed field values of cross relaxation. The effective g value of c * -direction in paramagnetic site is estimated as g c * =5.35. Using these values, the adiabatic and isolated susceptibilities are calculated which are in reasonable agreement with the observed susceptibilities. The antiferromagnetic susceptibility is estimated separated from the paramagnetic susceptibility. As temperature decreases, several cross relaxations have been revealed out subsequently, which seems to reflect the dynamic spin characters of antiferromagnetic ions.
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