Low Field Magnetic Susceptibility and the Hidden Order Transition in URu2Si2

TL;DR

This study investigates the hidden order transition in URu2Si2 using magnetization and susceptibility measurements, revealing complex magnetic signatures and potential symmetry breaking effects near the transition temperature.

Contribution

It provides new experimental insights into the magnetic behavior and signatures associated with the hidden order transition in URu2Si2, especially through higher-order susceptibility analysis.

Findings

Detection of a peak in AC susceptibility near 16 K

Observation of ferromagnetic signatures at 16 K and 35 K

Suppression of ferromagnetic signals in small magnetic fields

Abstract

Despite several decades of both experimental and theoretical work the nature of the hidden order transition at THO = 17.5 K in URu2Si2 remains enigmatic. We report here low field DC magnetization as well as AC susceptibility measurements performed on single crystals with field along the c-axis. A peak in the first order AC susceptibility is observed at T=16 K in close proximity to the well known change in slope at THO=17.5 K. Third order susceptibility measurements on the other hand reveal a signature only at 16 K with no discernible change at THO. However, both transitions are visible in the fifth order susceptibility. A signature at this lower transition, as a spontaneous ferromagnetic signal, also appears in low field DC magnetization measurements. A similar but larger ferromagnetic response appears at T~35 K. Both these ferromagnetic signatures are suppressed in a small field (B ~ 40 Gauss ||c-axis). The close proximity of the lower signature to the hidden order transition and the simultaneous presence and suppression of a ferromagnetic signature at 35 K could be due to the removal of degeneracy in the complex order-parameter of the hidden order transition due a "symmetry breaking field", at least locally within the crystals of URu2Si2.