Antiferromagnetism in Pr3In: Singlet/triplet physics with frustration

TL;DR

This study investigates antiferromagnetic order and singlet/triplet physics in Pr3In, revealing complex magnetic structures, low-temperature transitions, and frustration effects through neutron diffraction, susceptibility, and specific heat measurements.

Contribution

It provides the first detailed experimental characterization of magnetic order and frustration effects in Pr3In with singlet/triplet states.

Findings

Antiferromagnetic order below 12K with a modulated propagation vector.

Presence of a small ferromagnetic moment near 70K.

Neutron diffraction supports a model of ferromagnetic sheets with a twelve-unit-cell modulation.

Abstract

We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu3Au structure) compound Pr3In. This compound is believed to have a singlet (Gamma1) groundstate and a low-lying triplet (Gamma4) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T_N = 12K with propagation vector (0, 0, 0.5 +/-\delta) where \delta \approx 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 \mu_B magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 \mu_B) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at TN = 12K. This may be a consequence of the induced moment in the Gamma1 singlet, but may also be a sample-dependent effect.