[Paper Review] Antiferromagnetism and Hidden Order in Isoelectronic Doping of URu$_2$Si$_2$

M. N. Wilson, T. J. Williams+9 more|arXiv (Cornell University)|Dec 4, 2015

Rare-earth and actinide compounds3 citations

TL;DR

This study uses muon spin rotation (μSR) and susceptibility measurements to show that isoelectronic doping of URu₂Si₂ with Fe or Os preserves long-range antiferromagnetic order down to low doping levels (x = 0.02), with increasing internal fields indicating enhanced magnetic correlations. The results demonstrate that hybridization changes—not just structural effects—drive the evolution of magnetic order, challenging purely chemical pressure-based models of hidden order suppression in URu₂Si₂.

ABSTRACT

We present muon spin rotation ($μ$SR) and susceptibility measurements on single crystals of isoelectronically doped URu$_{2-x}$T$_x$Si$_2$ (T = Fe, Os) for doping levels up to 50\%. Zero Field (ZF) $μ$SR measurements show long-lived oscillations demonstrating that an antiferromagnetic state exists down to low doping levels for both Os and Fe dopants. The measurements further show an increase in the internal field with doping for both Fe and Os. Comparison of the local moment - hybridization crossover temperature from susceptibility measurements and our magnetic transition temperature shows that changes in hybridization, rather than solely chemical pressure, are important in driving the evolution of magnetic order with doping.

Motivation & Objective

• To investigate the stability of antiferromagnetic order and hidden order in URu₂Si₂ under isoelectronic doping with Fe and Os.
• To determine whether changes in magnetic order are driven by chemical pressure or hybridization effects.
• To resolve discrepancies in reported magnetic moments by comparing μSR data with neutron diffraction results.
• To clarify the role of hybridization in the suppression of hidden order and emergence of magnetic states.

Proposed method

• Conducted zero-field muon spin rotation (ZF-μSR) on single crystals of URu₂₋ₓTₓSi₂ (T = Fe, Os) with x up to 0.5 to probe local magnetic fields and long-range order.
• Measured magnetic susceptibility to determine the local moment - hybridization crossover temperature and compare it with the magnetic transition temperature.
• Analyzed the doping dependence of internal fields in ZF-μSR to infer changes in magnetic moment and ordering strength.
• Used neutron diffraction data from the same samples with improved normalization to resolve discrepancies in reported magnetic moments.
• Compared μSR results with previous neutron scattering and NMR data to assess consistency in magnetic volume fraction and moment size.
• Performed numerical analysis of muon stopping sites to evaluate their impact on measured internal fields.

Experimental results

Research questions

• RQ1 Does antiferromagnetic order persist in URu₂Si₂ under isoelectronic Fe and Os doping down to low doping levels?
• RQ2 Is the observed increase in internal field with doping due to enhanced magnetic moments or changes in muon stopping sites?
• RQ3 To what extent do hybridization effects, rather than chemical pressure, govern the evolution of magnetic order in doped URu₂Si₂?
• RQ4 Why do reported magnetic moments from neutron diffraction vary significantly from μSR measurements, and can this discrepancy be resolved?
• RQ5 Does the coexistence of hidden order and antiferromagnetism occur at low doping levels, as suggested by reduced magnetic volume fraction?

Key findings

• Antiferromagnetic order persists down to x = 0.02 in Fe-doped URu₂Si₂, as evidenced by long-lived oscillations in ZF-μSR measurements.
• The internal field in the μSR data increases with Fe and Os doping, indicating enhanced magnetic correlations despite minimal structural change.
• The magnetic transition temperature remains robust down to low doping, suggesting that hybridization effects—not just chemical pressure—are key drivers of magnetic order.
• Comparison of μSR data with neutron diffraction shows that previous magnetic moment measurements may have been inflated by unaccounted multiple scattering effects.
• The observed magnetic volume fraction decreases at x = 0.02, indicating possible coexistence of hidden order and antiferromagnetism in this regime.
• The results demonstrate that hybridization changes, not just lattice strain, are essential in understanding the suppression of hidden order in doped URu₂Si₂.