GD-155 MOSSBAUER-EFFECT AND MAGNETIC-PROPERTIES OF NOVEL RT(2)B(2)C2 COMPOUNDS WITH T-EQUIVALENT-TO-NI, CO

We have prepared the compounds GdNi2B2C and GdCo2B2C and investigated their magnetic properties by means of Gd-155 Mossbauer spectroscopy. F rom the temperature dependence of the hyperfine field, we derived that these two compounds give rise to magnetic ordering at 5.5+/-0.5 K and 21+/-1 K respectively. Large values of the electric field gradient V- ZZ were found, reminiscent of compounds of the related ThCr2Si2 type. A quantitative explanation of the origin of these field gradients is p resented by ab initio band structure calculations. The experimental va lues of V-ZZ have been used to estimate values for the second-order cr ystal field parameter in GdNi(2)B2C (A(2)(0) = -428Ka(0)(-2)) and GdCo 2B2C (A(2)(0) = -346Ka(0)(-2)).