In this work, we report on the thermomagnetic characterization and crystalline-electric field (CEF) energy scheme of the disordered defect-fluorite ${\mathrm{Ho}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$. This structural phase is distinguished by the coexistence of magnetic frustration and extensive disorder, with ${\mathrm{Ho}}^{3+}$ and ${\mathrm{Zr}}^{4+}$ sharing randomly the same $4a$ site with even 50% occupancy, and an average 1/8 oxygen vacancy per unit cell. AC magnetic susceptibility measurements performed on powder samples down to 0.5 K revealed signs of slowing spin dynamics without glassy behavior, including a frequency dependent peak at $\sim 1\mathrm{K}$. Yet, no evidence for long-range magnetic order is found down to 200 mK in the specific heat. Inelastic neutron scattering measurements show a weak, low-lying CEF excitation around 2 meV, accompanied by a broad level centered at 60 meV. To fit our observations, we propose an approach to account for structural disorder in the crystal-field splitting of the non-Kramers ${\mathrm{Ho}}^{3+}$. Our model provides an explanation to the broadening of the high-energy, single-ion excitations and suggests that the zirconate ground-state wavefunction has zero magnetic moment. Through the breaking of local symmetry, structural disorder enables the magnetic response observed in ${\mathrm{Ho}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$, allowing the mixing of low-lying states at finite temperatures. Finally, we show that this scenario is in good agreement with the bulk properties reported in this work.

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• Frustrated magnetism
• Spin liquid
• Disordered systems
• Fluorite structure
• Polycrystalline materials
• Pyrochlores
• Strongly correlated systems
• AC susceptibility measurements
• Adiabatic demagnetization
• Crystallography
• DC susceptibility measurements
• Inelastic neutron scattering
• Specific heat measurements