Charge density wave behavior and order-disorder in the antiferromagnetic metallic series Eu(Ga1-x Alx)4

The solid solution Eu(Ga1-xAlx)4 was grown in single crystal form to reveal a rich variety of crystallographic, magnetic, and electronic properties that differ from the isostructural end compounds EuGa4 and EuAl4, despite the similar covalent radii and electronic configurations of Ga and Al. Here we report the onset of magnetic spin reorientation and metamagnetic transitions for x=0-1 evidenced by magnetization and temperature-dependent specific heat measurements. TN changes nonmonotonously with x, and it reaches a maximum around 20 K for x=0.50, where the a lattice parameter also shows an extreme (minimum) value. Anomalies in the temperature-dependent resistivity consistent with charge density wave behavior exist only for x=0.50 and 1. Density functional theory calculations show increased polarization between the Ga-Al covalent bonds in the x=0.50 structure compared to the end compounds, such that crystallographic order and chemical pressure are proposed as the causes of the charge density wave behavior