COMMENSURATE MAGNETIC-STRUCTURES IN ER91.6-PERCENT-TM8.4-PERCENT

We have studied the magnetic behaviour of the alloy Er91.6%Tm8.4% usin g ultrasound, SQUID and neutron-scattering measurements. We have found that below 40 K the magnetic structure is very similar to the magneti c phase observed between 52 and 18 K in Er. However, high-order commen surate structures? which are stable over no more than approximately 2 K in pure Er, are stable over temperature ranges of up to 17 K in this alloy. Indeed, we find that in the region 26-18 K the magnetic struct ure is characterised by two modulation vectors. q = 2/7c and q = 4/15 c. We suggest that, on cooling, the modulation of the basal plane and c-axis components of the magnetisation become decoupled at 26 K, with the modulation of the basal plane component remaining locked into a v alue of q(b) = 2/7c, while the modulation of the c-axis component dec reases towards a value of q(c) = 4/15c. At 18 K the magnetic structur e reverts to a single q structure with q = 4/15c. (C) 1998 Elsevier S cience B.V. All rights reserved.