Pressure tuning of magnetic states in elemental thulium

Abstract

The magnetic and structural properties of elemental thulium were studied by means of neutron powder diffraction at pressures up to 5.5 GPa in the temperature range 7 – 290 K. At ambient pressure below TN = 52 K, the incommensurate magnetic state with a longitudinal sinusoidal modulation and propagation vector q = (0, 0, qz) was formed. The qz value increases on cooling from 0.279(2) and reaches the commensurate value of 2/7 at the temperature T1 = 24 K. The new magnetic arrangement is of an antiphase domain structure, composed of structural blocks involving three or four hexagonal layers with magnetic moment directions parallel within a given block and oppositely alternating from block to block along the c axis. Under high pressure, the TN value increases slightly up to 57 K at 5.5 GPa with a pressure coefficient dTN/dP = 0.9 K/GPa. The pressure dependence of the T1 temperature is more pronounced with a pressure coefficient dT1/dP = 2.9 K/GPa. The arrangement of commensurate magnetic structures formed below T1 is strongly pressure dependent. A formation of the complex magnetic states composed of structural blocks involving three or four hexagonal layers with magnetic moment signs alternating from block to block along the c axis with qz = 7/23 at 2 GPa and qz = 7/22 at 5.5 GPa was observed. The lattice compression of Tm at T = 7 K demonstrates a weak anisotropy with the most compressible c axis.