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

Abstract Several new MgZn 2 -type Laves phases with the P 6 3 / mmc symmetry and RE (Co 0.667 Ga 0.333 ) 2 stoichiometries ( RE  = Gd, Tb, Dy, Ho, and Er) were obtained by arc-melting and subsequent annealing. Single crystals with the MgZn 2 -type structure were extracted from the annealed RE (Co 0.667 Ga 0.333 ) 2 ( RE  = Gd, Tb, Dy, and Ho) alloys and Ga flux-grown Er(Co 0.667 Ga 0.333 ) 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(Co 0.667 Ga 0.333 ) 2 to Er(Co 0.667 Ga 0.333 ) 2 . RE atoms occupy the 4 f site, while Co and Ga are in the 2 a and 6 h sites. Magnetic behavior of the hexagonal MgZn 2 -type RE (Co 0.667 Ga 0.333 ) 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(Co 0.667 Ga 0.333 ) 2 phase were measured; the small isothermal magnetic entropy change (ΔS iso ) value of −4.94 J/kgK at 152 K and for a Δ H  = 0–50 kOe field change suggests a conventional magnetocaloric effect.