Second Low Temperature Phase Transition in Frustrated UNi_4B

Abstract

Hexagonal UNi_4B is magnetically frustrated, yet it orders antiferromagnetically at T_N = 20 K. However, one third of the U-spins remain paramagnetic below this temperature. In order to track these spins to lower temperature, we measured the specific heat C of \unib between 100 mK and 2 K, and in applied fields up to 9 T. For zero field there is a sharp kink in C at $T^{\ast }\approx$ 330 mK, which we interpret as an indication of a second phase transition involving paramagnetic U. The rise in $\gamma =C/T$ between 7 K and 330 mK and the absence of a large entropy liberated at $T^{\ast }$ may be due to a combination of Kondo screening effects and frustration that strongly modifies the low T transition.

4 pages, 4 figures

References in corpus (1)

• Kondo Screening and Magnetic Ordering in Frustrated UNi4B

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