Magnetic properties of single-crystalline CeCuGa${}_3$

The magnetic behavior of single-crystalline CeCuGa${}_3$ has been investigated. The compound forms in a tetragonal BaAl${}_4$-type structure consisting of rare-earth planes separated by site-disordered Cu-Ga layers. If the Cu-Ga site disorder is reduced, CeCuGa${}_3$ adopts the related, likewise tetragonal, BaNiSn${}_3$-type structure, in which the inversion symmetry is lost. We report on a detailed study of single crystals with the centrosymmetric structure variant which exhibit ferromagnetic order below $\approx$4 K with a strong, planar anisotropy. The magnetic behavior above the transition temperature can be well understood by the crystal-field splitting of the 4$f$ Hund's rule ground-state multiplet ${}^2{F}_{5/2}$ of Ce${}^{3+}$.

Figure 1

Two possible tetragonal crystal structures of $R$Cu${}_x$Ga${}_{4-x}$. If Cu and Ga occupy the 4$d$ and 4$e$ sites randomly, the BaAl${}_4$ structure is adopted. For the stoichiometric compound $x=1$ the Cu and Ga ions can order, resulting in the related noncentrosymmetric BaNiSn${}_3$-type structure.

Figure 2

Reconstruction of the $h$1$l$ plane of the reciprocal space from single-crystal x-ray diffraction data. The arrows are pointing to the first- and second-order satellite reflections. The circles show the third-order satellites on the positions of forbidden reflections from the body-centered lattice.

Figure 3

(a) Magnetic susceptibility of CeCuGa${}_3$ under zero-field-cooled (ZFC) and field-cooled (FC) conditions for $H\parallel \left[100\right]$ and under FC condition for $H\parallel \left[001\right]$ as a function of temperature. (b) ac susceptibility with $H\parallel \left[100\right]$ and at frequencies of 5 and 938 Hz. (c) Low-temperature specific heat of CeCuGa${}_3$ showing the anomaly at the magnetic phase transition.

Figure 4

The susceptibility $\chi =M/H$ of CeCuGa${}_3$ for $H\parallel \left[100\right]$ as a function of $T$ in low magnetic fields. The curves are shifted with respect to one another for a better readability.

Figure 5

Magnetic hysteresis loop $M\left(H\right)$ of CeCuGa${}_3$ measured at 2 K for $H\mid \mid \left[100\right]$. The low-field $\left(M\right)$ for $H\mid \mid \left[001\right]$ is also shown.

Figure 6

Magnetic isotherms of CeCuGa${}_3$ at 2 K with field applied along the $\left[100\right]$ and $\left[001\right]$ directions.

Figure 7

The inverse dc susceptibility of CeCuGa${}_3$ after subtraction of the temperature-independent electronic contribution, ${(\chi -{\chi }_0)}^{-1}$, as a function of $T$ for $H\parallel \left[100\right]$ and $\left[001\right]$. The black lines are fits to the crystal-electric-field (CEF) model described in the text.

Figure 8

(a) The specific heat of CeCuGa${}_3$ and LaCuGa${}_3$ plotted as $C/T$ vs $T$. The inset shows $C/T$ as a function of $T^2$. The linear fit was used to extract the Sommerfeld constant. (b) The $4f$ contribution to the specific heat of CeCuGa${}_3$ with a fit to the Schottky anomaly as described in the text. The inset shows the calculated $4f$ contribution to the entropy.

Figure 9

Resistivity of CeCuGa${}_3$ $\rho \left(T\right)$ and its counterpart LaCuGa${}_3$ without 4$f$ electrons ${\rho }_{\mathrm{La}}\left(T\right)$ which was used to estimate the magnetic contribution ${\rho }_{\mathrm{mag}}\approx \rho -{\rho }_{\mathrm{La}}$. The inset shows the low-temperature resistivity of CeCuGa${}_3$.