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arXiv · 2412.08043

YbNi$_4$Mg: Superheavy fermion with enhanced Wilson ratio and magnetocaloric effect

Xiaoci Zhang·Te Zhang·Zhaotong Zhuang·Zixuan Leng·Zixuan Wei·Xinyang Liu·Junsen Xiang·Shuai Zhang·Peijie Sun
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Abstract

A comprehensive study of the low-temperature properties of YbNi$_4$Mg has revealed evidence of a superheavy-fermion state, characterized by a large electronic specific-heat coefficient $\gamma_0$ $\approx$ 5.65 J mol$^{-1}$ K$^{-2}$ and an elevated Wilson ratio $R_W$ = 32.1. No magnetic ordering was observed down to 70 mK; however, a broad maximum appears in the specific heat at $T^*$ = 0.3 K, along with a shoulder in the derivative of susceptibility d$\chi$/d$T$ and resistivity d$\rho$/d$T$. These features indicate a cooperative yet short-ranged magnetism entwined with the superheavy Fermi liquid. The large Wilson ratio, which is also detected in other superheavy-fermion compounds lacking long-range order, might be a signature of residual spin fluctuations. Applying a weak magnetic field of $\sim$0.1 T induces a metamagnetic-like crossover, as demonstrated by the quasi-adiabatic demagnetization measurements showing a broad minimum in the temperature-field trace. Here, an enhanced magnetocaloric cooling effect stemming from the field-sensitive superheavy-fermion state is observed, rivaling that of the well-established insulating magnetic coolants like the rare-earth garnet Gd$_3$Ga$_5$O$_{12}$.

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Xiaoci Zhang, Te Zhang, Zhaotong Zhuang, Zixuan Leng, Zixuan Wei, Xinyang Liu, Junsen Xiang, Shuai Zhang, Peijie Sun. 2024-12-11. YbNi$_4$Mg: Superheavy fermion with enhanced Wilson ratio and magnetocaloric effect. https://arxiv.org/abs/2412.08043

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