Pressure evolution of coplanar antiferromagnetism in heavy-fermion Ce$_{2}$CoAl$_{7}$Ge$_{4}$

Abstract

Ce$_{2}$$M$Al$_{7}$Ge$_{4}$ ($M=$ Co, Ir, Ni or Pd) are heavy-fermion materials and host a variety of ground states ranging from magnetism to non-Fermi liquid behavior. The Co, Ir, and Ni members of the series undergo magnetic ordering with decreasing transition temperatures. In contrast, the Pd compound does not magnetically order down to 0.4 K and shows non-Fermi liquid behavior, suggesting proximity to a magnetic quantum critical point. Among the series, Ce$_{2}$CoAl$_{7}$Ge$_{4}$ orders antiferromagnetically below $T_N=1.9$ K along with heavy-fermion behavior below 15 K. We report the magnetic structure of the antiferromagnetic phase in Ce$_{2}$CoAl$_{7}$Ge$_{4}$ and the evolution of the magnetic transition under external pressure. Rietveld refinement of the neutron diffraction data suggests a coplanar antiferromagnetic structure with a wave vector $k = (1,1,1)$ and an ordered moment of $0.383 \pm 0.018 \> \mu_B$ in the antiferromagnetic phase. Electrical resistivity and AC calorimetry measurements under hydrostatic pressure reveal a suppression of the antiferromagnetic transition toward zero temperature around $p=1.1$ GPa. However, there is no evidence of non-Fermi liquid behavior associated with the suppression of magnetism by pressure, unlike the effect of transition-metal substitution.