Structural and magnetic ordering of CrNb$_{3}$S$_{6}$ single crystals grown by gas transport method

Paramagnetic layered semiconductor NbS$_2$ doped with some transition metals can transform into ferromagnetic material. That is why such materials are promising candidates for spintronic devices. It is found that only at certain concentrations of a doping metal $T$ crystallographic ordering is possible, which is essential for magnetic ordering of ternary compounds $T$NbS$_2$. In particular, CrNb$_{3}$S$_{6}$ crystals are studied, which form almost completely ordered superstructure with intercalated Cr between NbS$_2$ layers. The main difficulty in crystal growth is reaching stoichiometry of the compound. This problem is solved in the developed method of two-staged gas transport chemical reaction. This new approach provides growth of CrNb$_{3}$S$_{6}$ single crystals of several millimeters in diameter and 0.3–0.5 mm thickness. X-ray phase analysis (XRD) of powders is performed to identify all phases involved in synthesis and growth of the crystals. High frequency absorption in external periodic magnetic field as a function of temperature and intensity of magnetic field is used to estimate the temperature of ferromagnetic transition in CrNb$_{3}$S$_{6}$ single crystals. The Curie temperature is estimated as 115 K. Growth of CrNb$_{3}$S$_{6}$ crystals from vapor phase is studied in detail and full analysis of phase transitions during growth is given. It has been shown that using of high frequency absorption in the crystal provides reliable estimation of the point of ferromagnetic transition in this semiconductor.