Crystal structures of new R3CoAl3Ge2 (R = Gd–Er) quaternary compounds and magnetic properties and lattice thermal expansion of Gd3CoAl3Ge2

• New R3CoAl3Ge2 (R = Gd–Er) quaternary compounds was detected.
• R3CoAl3Ge2 is isostructural with YNi3Al3Ge2 and has space group of P6¯2m.
• The structure of Gd3CoAl3Ge2 was successfully refined by using Rietveld method.
• The lattice thermal expansion of Gd3CoAl3Ge2 was studied in a temperature range of 298–688 K.
• The magnetic measurements of Gd3CoAl3Ge2 were performed.

The crystal structures of new R3CoAl3Ge2 (R = Gd–Er) quaternary compounds were studied by X-ray powder diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy techniques. The novel R3CoAl3Ge2 (R = Gd–Er) compounds crystallizes in a hexagonal Y3NiAl3Ge2-type structure with space group P6¯2m (No. 189). The crystal structure of Gd3CoAl3Ge2 was refined by Rietveld method. The lattice thermal expansion of the Gd3CoAl3Ge2 compound was investigated in a temperature range from 298 K to 688 K. The linear lattice thermal expansion coefficients of Gd3CoAl3Ge2 along a and c axes are calculated to be αa = 8.766 × 10−6 K−1, αc = 5.534 × 10−6 K−1, respectively. The linear thermal expansion coefficient of the unit cell volume of Gd3CoAl3Ge2 is αV = 22.84 × 10−6 K−1. The magnetic measurement of Gd3CoAl3Ge2 was performed in the temperature range of 4–300 K by using MPMS-SQUID magnetometer. The experimental effective magnetic moment (μeff) is calculated to be 7.01 μB per Gd atom and paramagnetic Currie temperature θ = −23.8(3) K under an applied field of 1kOe. The magnetic measurements of Gd3CoAl3Ge2 show antiferromagnetic ordering at lower temperature.