Structural and magnetic studies on the new Laves phases RE(Co0.667Ga0.333)2 (RE=Gd, Tb, Dy, Ho, and Er). Magnetocaloric effect of Gd(Co0.667Ga0.333)2

Several new MgZn2-type Laves phases with the P63/mmc symmetry and RE(Co0.667Ga0.333)2 stoichiometries (RE=Gd, Tb, Dy, Ho, and Er) were obtained by arc-melting and subsequent annealing. Single crystals with the MgZn2-type structure were extracted from the annealed RE(Co0.667Ga0.333)2 (RE=Gd, Tb, Dy, and Ho) alloys and Ga flux-grown Er(Co0.667Ga0.333)2 sample. Powder and single-crystal X-ray diffraction methods were used for the phase analysis and structural characterization. A decrease in the cell volume due to the lanthanide contraction is observed from Gd(Co0.667Ga0.333)2 to Er(Co0.667Ga0.333)2. RE atoms occupy the 4f site, while Co and Ga are in the 2a and 6h sites. Magnetic behavior of the hexagonal MgZn2-type RE(Co0.667Ga0.333)2 phases strongly depends on the RE. Apparent ferromagnetic transition is observed for RE=Gd, Tb, and Dy, while the other two phases (RE=Ho, and Er) seem to be ferrimagnetic. Magnetocaloric properties of the Gd(Co0.667Ga0.333)2 phase were measured; the small isothermal magnetic entropy change (ΔSiso) value of −4.94J/kgK at 152K and for a ΔH=0–50kOe field change suggests a conventional magnetocaloric effect.