ИСТИНА

In the present work we investigate the magnetic susceptibility and specific heat of Pb3TeCo3V2O14 and Pb3TeMn3As2O14 in the range 1.8–350 K.Temperature dependences of the magnetic susceptibility χ(T) of Pb3TeCo3V2O14 and Pb3TeMn3As2O14 follow the Curie-Weiss law in the range 20–350 K. The values of the effective magnetic moment are 4.3μB for Co2+ in Pb3TeCo3V2O14 and 5.1μB for Mn2+ in Pb3TeMn3As2O14. The Neel temperatures TN determined as a maxima of χ(T) are 10.8 K for Pb3TeCo3V2O14 and 7.1 K for Pb3TeMn3As2O14. For Pb3TeCo3V2O14 we found the double peak structure on the ∂χ/∂Т curve. This double anomaly was also found in the specific heat temperature dependence C(T) for Pb3TeCo3V2O14. The anomalies are seen at T1 = 8.9 К and Т2 = 6.3 К. Below TN the C(T) curve shows exponential decrease. The Debye temperature for Pb3TeCo3V2O14 is ΘD = 350 K. For Pb3TeMn3As2O14 the C(T) curve shows almost linear behavior down to 1.8 K. The scaling procedure using the C(T) data of nonmagnetic analogue Pb3TeZn3As2O14 in a range 1.8–80 K gave the magnetic entropy 34 J/mol K for Pb3TeCo3V2O14 and 46 J/mol K for Pb3TeMn3As2O14 that agrees well with theoretical estimations 34.6 and 44.7 J/mol K. Unusual properties of Pb3TeCo3V2O14 and Pb3TeMn3As2O14 allow predicting the multiferroic features of them. Lately the multiferroic properties of Fe-based langasite family compound were discovered. The magnetic ordering in Ba3NbFe3Si2O14 is accompanied by anomalies of crystal lattice parameter, dielectric permittivity and polarization.