Growth of ultra-clean single crystals of RuO2

TL;DR

This paper details the growth process of ultra-clean RuO2 single crystals with controlled morphology, high purity, and no magnetic ordering, suitable for altermagnetism research.

Contribution

It introduces a refined sublimation transport method with a specialized growth tube to produce high-quality RuO2 crystals with various morphologies.

Findings

Crystals with residual resistivity of about 30 nOhmcm

Residual resistivity ratio (RRR) up to 1200

No signs of magnetic ordering down to low temperatures

Abstract

We report the details of the growth of ultra-clean single crystals for RuO2, a candidate material for altermagnetism. By using a crystal-growth tube with a necking structure and precisely controlling the conditions of the sublimation transport method, it is possible to control the morphology of the crystals. We obtained crystals in mainly three kinds of morphology: thick plate-like crystals typically 5 x 3 x 2mm3 and up to 10 x 5 x 2mm3 with a large (101) facet, rhombohedral columnar crystals elongating along the [001] direction, and fiber and needle crystals of length up to 8 mm and the width of 0.1-0.4 mm. These crystals show residual resistivity of about 30 nOhmcm and a residual resistivity ratio (RRR) up to 1200. The crystals do not exhibit any signs of magnetic ordering down to low temperatures.