Field-temperature phase diagram of the enigmatic Nd$_2$(Zr$_{1-x}$Ti$_x$)$_2$O$_7$ pyrochlore magnets

TL;DR

This study maps the magnetic phase diagram of Nd2(Zr1-xTix)2O7 pyrochlore magnets using neutron scattering and magnetization measurements, revealing how Ti substitution influences phase stability and transitions at very low temperatures.

Contribution

It provides the first detailed (H,T) phase diagram for these compounds, showing that Ti substitution enhances the stability of the all-in/all-out phase and affects field-induced transitions.

Findings

The ground state remains all-in / all-out across samples.

Moderate Ti substitution increases the stability of the all-in / all-out phase.

Field-induced transitions show metamagnetic singularities.

Abstract

By combining neutron scattering and magnetization measurements down to 80 mK, we determine the $(H,T)$ phase diagram of the Nd$_2$(Zr$_{1-x}$Ti$_x$)$_2$O$_7$ pyrochlore magnet compounds. In those samples, Zr is partially substituted by Ti, hence tuning the exchange parameters and testing the robustness of the various phases. In all samples, the ground state remains "all in / all out", while the field induces phase transitions towards new states characterized by "2 in - 2 out" or "1 out - 3 in / 1 in - 3 out" configurations. These transitions manifest as metamagnetic singularities in the magnetization vs field measurements. Strikingly, it is found that moderate substitution reinforces the stability of the "all in / all out" phase: the N\'eel temperature, the metamagnetic fields along with the ordered magnetic moment are higher in substituted samples with $x <$ 10\%.