Structural and magnetic properties of Nd2Fe14-xSixB compounds and related hydrides

The synthesis and characterisation of Nd2Fe14-xSixBHy compounds is presente d for x=0 to 2 and y=0 to 4. The samples have been studied both from the st ructural aspect and the magnetic properties. Magnetisation measurements hav e been carried out for all studied compositions at both 5 and 300 K in fiel ds up to 7 T. The effects of Si substitution and/or H insertion on the spin reorientation that occurs at low temperature have been investigated by mea ns of AC susceptibility measurements. On one hand the effects of Si and H o n the unit cell volume and the saturation magnetisation are found to be opp osite (decrease for Si and increase for H); on the other hand their effect on the Curie temperature is similar with a dramatic enhancement. An evoluti on of the magnetic properties versus Si and/or ii content is presented and analyzed. We also report on the evolution of the maximum hydrogen uptake ve rsus the Si concentration. it decreases when x increases. The reasons for t his are discussed in the light of earlier reported neutron diffraction resu lts concerning the H location and the preferential occupancy of some Fe sit es by Si. Finally a comparison is made with related R2Fe17-xSixHy systems. (C) 1999 Elsevier Science S.A. All rights reserved.