Magnetostructural phase transitions and magnetocaloric effect in Tb-Dy-Ho-Co-Al alloys with a Laves phase structure

Abstract

The influence of simultaneous substitution within the rare earth (R) and Co sublattices on the structural, magnetic, and magnetocaloric properties of the Laves phase RCo2-type compounds is studied. Main attention is devoted to the studies of the magnetostructural phase transitions and the transition types with respect to the alloy composition. Multicomponent alloys Tbx(Dy0.5Ho0.5)1 xCo2 and Tbx(Dy0.5Ho0.5)1 xCo1.75Al0.25 were prepared with the use of high purity metals. Majority of the Tbx(Dy0.5Ho0.5)1 xCo2 alloys exhibit magnetic transitions of the first-order type and a large magnetocaloric effect. The substitution of Al for Co in Tbx(Dy0.5Ho0.5)1 xCo2 increases the Curie temperature (TC) but changes the transition type from first-to the second-order. The discussion of the physical mechanisms behind the observed phenomena is given on the basis of the first principles electronic-structure calculations taking into account both the atomic disorder and the magnetic disorder effects at finite temperatures. The advantage of Al-containing materials is that sufficiently high magnetocaloric effect values are preserved at T>TC.