Onset of ferromagnetism in the 5f-band metamagnet UCoAl upon partial dilution of the U sublattice

UCoAl is a 5f-band metamagnet. The U1-xRxCoAl solid solutions with R=Lu and Y exhibit ferromagnetism for low R content. The spontaneous magnetic momen t reaches a maximum value of 0.09 mu(B), and 0.21 mu(B) at x=0.06 for R=Lu and Y, respectively, and vanishes at x greater than or equal to 0.15. The e volution of crystal structure parameters together with magnetism are compar ed for U1-xLuxCoAl, U1-xYxCoAl and also for UCoAl1-xXx (X=Ga, In, Sn). It i s concluded that the linear changes of lattice dimensions rather that the u nit cell volume play a principal role in determining the ground state prope rties of UCoAl related compounds. The decrease of the c/a ratio in these ma terials correlates with the transformation from the metamagnetic to a ferro magnetic state. (C) 2000 Elsevier Science S.A. All rights reserved.