Single crystal growth and anisotropic magnetic properties of HoAl2Ge2

Abstract

We have grown a single crystal of HoAl2Ge2, which crystallizes in the hexagonal CaAl2Si2 type structure with Ho ions in the trigonal coordination in the ab plane. The data obtained from the bulk measurement techniques of magnetization, heat capacity and transport reveal that HoAl2Ge2 orders antiferromagnetically at TN ∼6.5 K. The susceptibility below TN and isothermal magnetization at 2 K indicate the ab plane as the easy plane of magnetization. Heat capacity data reveal a prominent Schottky anomaly with a broad peak centered around 25 K, suggesting a relatively low crystal electric field (CEF) splitting. The electrical resistivity reveals the occurrence of a superzone gap below TN. The point charge model of the CEF is applied to the magnetization and the heat capacity data. While a good fit to the paramagnetic susceptibility is obtained, the CEF parameters do not provide a satisfactory fit to the isothermal magnetization at 2 K and the Schottky anomaly.

Anisotropic magnetic properties of trigonal ErAl2Ge2 single crystal

“…The electrical resistivity decreases with the decrease in temperature typical of a metal and shows an upturn below 4 K, which is due to the onset of antiferromagnetic ordering (see magnetization data below). Similar upturn in the electrical resistivity was observed in the isostructural compound HoAl 2 Ge 2 [11], below its Néel temperature. The increase in the electrical resistivity in the antiferromagnetic state is usually attributed to the formation of superzone gap, when the magnetic periodicity is different from the lattice periodicity.…”

“…The susceptibility in the ab-plane increases more rapidly below 20 K than along the c-axis, thus indicating that the easy axis of magnetization is inclined more towards the ab-plane. Similar behaviour was previously observed in HoAl 2 Ge 2 [11]. The inverse susceptibility data were fitted to the modified Curie-Weiss law,…”

“…Previously, we used the same approximation for analysing the anisotropic magnetic properties of isostructural HoAl 2 Ge 2 [11]. The 16-fold (2J + 1; J = 15/2) degenerate level of free Er 3+ ion splits into 8 doublets in the CEF of hexagonal symmetry.…”

“…We have reported the physical properties of EuAl 2 Si 2 single crystal [10], which orders antiferromagnetically at 33 K and exhibits a substantially large magnetoresistance ( 1200 % at 14 T) at 2 K for the field applied along the c-axis. Very recently, we reported the magnetic properties of HoAl 2 Ge 2 single crystal [11] which undergoes a bulk antiferromagnetic transition at 6.5 K with the ab-plane as the easy plane of magnetization. In continuation of our studies on this series of compounds we have successfully grown the single crystals of ErAl 2 Ge 2 and probed the magnetic behavior using the techniques of magnetization, electrical resistivity and heat capacity.…”