The type of the magnetic phase transition in the R(Co1-xAlx)2 (R=Dy, Ho, Er) compounds is
studied by means of magnetization, thermal-expansion and electrical-resistivity measurements. With
increasing Al content, a change from a first-order to a second-order transition is observed, at x?0.075, 0.075
and 0.025 for Er, Ho and Dy, respectively. An explanation is offered in terms of the Inoue-Shimizu model
by introducing a concentration dependence of T3, the temperature at which a3(T) changes sign (a3 is the
coefficient of the M4
d-term in the expansion of the free energy of the d-subsystem). In fact, T3 is taken
proportional to Tm, the temperature at which the susceptibility of the corresponding Y(Co, Al)2 shows a
maximum. ?? 1992.
