Cystal Structures And Magnetic Properties Of New R₂TAl₄Ge₂ And R₃CoAl₃Ge₂（R=Y, Gd, Tb, Dy, Ho, T=Fe, Co） Compounds

The new R3CoAl3Ge2 (R= Gd, Tb, Dy, Ho, Er), R2CoAl4Ge2 (R=Y, Gd, Tb, Dy, Ho, Er) quaternary compounds and R2FeAl4Ge2 (R=Y, Gd, Tb, Dy, Ho, Er) have been synthesized and studied by X-ray powder diffraction, scanning electron microscope equipped with energy dispersive spectroscopy. The crystal structures of three new compounds were refined by using Rietveld method. The magnetic properties of some comopounds were investigated by materials property measured system (MPMS) and superconducting quantum interference device (SQUID)1. The new R3CoAl3Ge2 (R= Gd, Tb, Dy, Ho, Er) compounds crystallized in the hexagonal Al3Ge2NiY3 type structure with space group P62m (No.189). The lattice parameters of Gd3CoAl3Ge2 are a=0.69733(2) nm and c=0.42027(2) nm, respectively. The crystal structure of Gd3CoAl3Ge2 was successfully refined by Rietveld method. The lattice thermal expansion of the Gd3CoAl3Ge2 compound was investigated in a temperature range from 298K to 688K. The linear lattice thermal expansion coefficients of Gd3CoAl3Ge2 along a and c axes are calculated to be αa=8.766×10-6K-1, αc=5.534×10-6K-1, respectively. The linear thermal expansion coefficient of the unit cell volume of Gd3CoAl3Ge2 is av=22.84×10-6K-1. The magnetic measurement of Gd3CoAl3Ge2 was performed in the temperature range of 5-300K 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.2. The new R2CoAl4Ge2 (R=Y, Gd, Tb, Dy, Ho, Er) quaternary compounds crystallized in the tetragonal Tb2NiAl4Ge2-type structure with space group I4/mmm (No.139). The lattice parameters of Gd2CoAl4Ge2 are a=0.41443(2) nm and c=1.95657 (7) nm, respectively. The magnetic measurements of Gd2CoAl4Ge2 show antiferromagnetic ordering at lower temperature. The susceptibility of Gd2CoAl4Ge2 is followed perfectly by Curie-Weiss behavior in high temperature region, giving the effective magnetic moment ηeff=8.10μB (per Gd atom) and the paramagnetic Curie temperature δp=-31.1K.3. The new R2FeAl4Ge2 (R=Y, Gd, Tb, Dy, Ho, Er) quaternary compounds also crystallized in the tetragonal Tb2NiAl4Ge2 structure type with space Group I4/mmm (No.139). The lattice parameters of Gd2FeAl4Ge2 are a=0.41600(2) nm and c= 1.96913(8)nm. Similar to Gd2CoAl4Ge2, Gd2FeAl4Ge2 also shows antiferromagnetic ordering at lower temperature and the susceptibility of Gd2FeAl4Ge2 is followed perfectly by Curie-Weiss behavior in high temperature region. The effective magnetic moment μeff of Gd2FeAl4Ge2 is 8.27μB and the paramagnetic Curie temperature θp=-13.7K.