We determined the fundamental parameters and analyzed the chemical composition for 20 G and K giants within 150 pc from the Sun, for which the magnetic fields Bmax from 0.3 to 98.6 G have been detected. Abundances of 18 chemical elements from lithium (Z=3) to hafnium (Z=72) are derived. From infrared CN molecular lines the nitrogen abundance and the carbon isotope ratio 12C/13C are determined. The low values 12C/13C = 7-26 for most of the giants prove that they were passed through the deep convecting mixing during the First Dredge-Up (FDU) evolutionary phase.
Lithium is detected in spectra of 16 of 20 giants studied. A presence of lithium in atmospheres of giants passed through the deep mixing during the FDU phase contradicts the theory. The pronounced correlation between the [N/C] and [N/O] values is found, which has an evolutionary nature. A comparison of this relation with theoretical models calculated for rotating stars shows that it reflects mainly the dependence of these two values on the initial rotational velocity. The total C+N+O abundance that should be constant during the star’s evolution is found to be correlated with [Fe/H]. This correlation can be explained partially by the known [O/Fe] vs [Fe/H] relation. The anticorrelation between the [El/Fe] and [Fe/H] values for rare earth (RE) elements is obtained. The relations for both the sum C+N+O and the RE elements reflect the initial chemical composition of the giants. No marked systematic differences in the element abundances are found between the magnetic and non-magnetic giants.