HfTe2: Enhancing Magnetoresistance Properties by Improvement of the Crystal Growth Method.

We present a systematic study on the magnetotransport properties of HfTe2 single crystals grown by different synthetic protocols. Both chemical vapor transport (CVT) as well as the self-flux method were applied. Depending on the synthetic procedure the crystal quality is reflected by the residual resistivity ratio (RRR). The best CVT grown crystal shows a RRR of 262, while the crystal with the highest quality obtained with the Te self-flux method exhibits a value of 404. The superiority of the self-flux method can be traced back to its ability to reduce the amount of Zr as main contaminant more effectively compared to chemical vapor transport. The large RRR value is reflected in the magnetoresistance (MR) effect which reaches more than 9400%, outperforming the data published for HfTe2. The benefit of the self-flux approach was tested for WTe2 and a RRR of 2525 was reached significantly surpassing the data reported in literature. Crystals of both high and low RRR were compared with respect to the magnetotransport properties, i.e., transverse magnetoresistance and the Hall effect. The major factor determining the maximum value of the MR is the carrier mobility which is severely affected by the preparation conditions, while the carrier balance remains virtually unaffected.