PSEUDO-QUATERNARY BORO-CARBIDES - A 2-SUB-LATTICE MODEL

We consider recently studied boro-carbides RE(Ni1-xMx)(2)B2C, with emp hasis in RE = Y and Ho. Ho compounds exhibit in some cases spiral magn etic order. We extended a recent previous work on Heusler compounds to study the specific heat of Y boro-carbides doped with Co and to calcu late the coupling between Ho moments in neighbouring planes. The effec t of impurity disorder is included in the electronic structure via the Coherent Potential Approximation (CPA) and in the absence of experime ntal data for the pseudoquaternary specific heat, we restricted oursel ves to the dilute limit and determine the impurity potential via Fried el's sum rule. The electron-phonon coupling (lambda(x)) is extracted f rom the measured superconducting transition temperature, using the Ali en-Dines formula. The existent specific heat data for Y compounds is u sed to fix the parameters of the two sub-lattice model. Finally we stu dy the change, with transition metal concentration, of the angle betwe en moments of the spiral magnetic order. (C) 1998 Published by Elsevie r Science B.V. All rights reserved.