Magnetic ordering of novel La3NiGe2-type R3CoGe2 compounds (R = Pr, Nd, Sm, Gd–Dy)

The novel R3CoGe2 compounds adopt the La3NiGe2-type structure (space group Pnma) with the following cell parameters: a = 1.1706(1), b = 0.42267(5), c = 1.1242(1) nm for Sm3CoGe2; a = 1.15845(5), b = 0.41905(2), c = 1.12088(5) nm for Gd3CoGe2; a = 1.14942(4), b = 0.41705(2), c = 1.11030(4) nm for Tb3CoGe2 and a = 1.1431(2), b = 0.41500(5), c = 1.1040(2) nm for Dy3CoGe2. The R3CoGe2 compounds undergo a ferrimagnetic type ordering (TCN = 150 K for Gd3CoGe2). Neutron diffraction studies show that Pr3CoGe2 and Nd3CoGe2 have a commensurate ferromagnetic component along the a axis and a commensurate antiferromagnetic component along the c axis (Pn’ma magnetic space group): (MPrF)a = 2.59(9) μB, (MPrAF)c = 1.58(4) μB, ∣MPr∣ = 3.03(9) μB for Pr3CoGe2 and (MNdF)a = 2.6(1) μB, (MNdAF)c = 1.65(6) μB, ∣MNd∣ = 3.1(1) μB for Nd3CoGe2 at 2 K. ocaloric effect of Gd3CoGe2 in terms of the isotherm entropy change, ΔSiso, was derived from the magnetization measurement, and it reaches the maximum value of ΔSiso = −4.9 J/kg•K in the 139–144 K temperature range.