Evaluating the Effects of Structural Disorder on the Magnetic Properties of Nd$_{2}$Zr$_{2}$O$_{7}$

TL;DR

This study investigates how structural disorder, influenced by synthesis conditions, affects the magnetic properties of Nd$_{2}$Zr$_{2}$O$_{7}$ crystals, revealing that near-stoichiometric growth preserves magnetic features like moment fragmentation.

Contribution

It demonstrates that high-pressure Ar growth yields nearly stoichiometric Nd$_{2}$Zr$_{2}$O$_{7}$ crystals with magnetic properties similar to powders, highlighting the impact of disorder on magnetic behavior.

Findings

Crystals grown under atmospheric conditions show reduced lattice parameters due to Zr stuffing.

High-pressure Ar-grown crystals are nearly stoichiometric with lattice parameters close to powders.

Magnetic properties, including moment fragmentation, are preserved in nearly stoichiometric crystals.

Abstract

Motivated by the variation in reported lattice parameters of floating-zone-grown Nd$_{2}$Zr$_{2}$O$_{7}$ crystals, we have performed a detailed study of the relationship between synthesis environment, structural disorder, and magnetic properties. Using a combination of polycrystalline standards, electron-probe microanalysis and scattering techniques, we show that crystals grown under atmospheric conditions have a reduced lattice parameter - relative to pristine polycrystalline powders - due to occupation of the Nd-site by excess Zr (i.e. "negative" stuffing). In contrast, crystals grown under high-pressure Ar are nearly stoichiometric with an average lattice parameter approaching the polycrystalline value. While minimal disorder of the oxygen sublattices is observed on the scale of the average structure, neutron pair-distribution function analysis indicates a highly local disorder of the oxygen coordination, which is only weakly dependent on growth environment. Most importantly, our magnetization, heat capacity and single-crystal neutron scattering data show that the magnetic properties of crystals grown under high-pressure Ar match closely with those of stoichiometric powders. Neutron scattering measurements reveal that the signature of magnetic moment fragmentation - the coexistence of all-in-all-out (AIAO) magnetic Bragg peaks and diffuse pinch-point scattering due to spin-ice correlations - persists in these nearly stoichiometric crystals. However, in addition to an increased AIAO transition temperature, the diffuse signal is seemingly stabilized and remains nearly unchanged upon warming to 800 mK. This behavior indicates that both the AIAO magnetic order and spin-ice correlations are sensitive to deviations of the Nd stoichiometry.