The type of the magnetic phase transition in the R(Co_1-xAl_x)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 T_m, the temperature at which the susceptibility of the corresponding Y(Co, Al)₂ shows a maximum. © 1992.

Duc N.H., Hien T.D., Levitin R.Z., Markosyan A.S., Brommer P.E., Franse J.J.M.

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Từ khóa : Dysprosium Compounds--Phase Transitions; Electric Conductivity; Magnetization; Rare Earth Compounds--Thermal Expansion; Inoue-Shimizu Model; Rare Earth Compounds