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Register a new userEvolution of the partially frustrated magnetic order in CePd$_{1-x}$Ni$_x$Al
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We report on a single-crystal neutron diffraction study of the evolution of the antiferromagnetic order in the heavy-fermion compound CePd$_{1-x}$Ni$_x$Al which exhibits partial geometric frustration due to its distorted Kagome structure. The magnetic structure is found to be unchanged with a propagation vector $Q_mathrm{AF} approx (0.5~0~0.35)$ for all Ni concentrations $x$ up to $x_c approx 0.14$. Upon approaching the quantum critical concentration $x_c$, the ordered moment vanishes linearly with Neel temperature $T_{rm N}$, in good agreement with CePdAl under hydrostatic pressure. For all Ni concentrations, substantial short-range magnetic correlations are observed above $T_{rm N}$ as a result of frustration.
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In the heavy-fermion metal CePdAl long-range antiferromagnetic order coexists with geometric frustration of one third of the Ce moments. At low temperatures the Kondo effect tends to screen the frustrated moments. We use magnetic fields $B$ to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with $B$ employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.
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We use a combination of the coherent potential approximation and dynamical mean field theory to study magnetic properties of the Fe$_{1-x}$Ni$_x$ alloy from a first principles. Calculated uniform magnetic susceptibilities have a Curie-Weiss-like behavior and extracted effective temperatures are in agreement with the experimental results. The individual squared magnetic moments obtained as function of nickel concentration follow the same trends as experimental data. An analysis of the ionic and spin weights shows a possibility of a high-spin to intermediate- and low-spin states transitions at high temperatures.
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