High pressure effects on magnetic states of elemental holmium

Abstract

The pressure response of the magnetic and structural properties of elemental holmium was explored by means of neutron powder diffraction in the pressure range up to 8.7 GPa and the temperature range 7 – 290 K. At ambient pressure, below TN = 127 K the incommensurate helical state with a propagation vector q = (0 0 qz) is evidenced. On temperature lowering, the qz value decreases from 0.270c* (at 125 K) to 5/26c* at TL = 20 K. Below the lock-in transition temperature TL, a commensurate cone structure is formed due to canting of magnetic moments towards the c axis. Upon lattice compression, a gradual suppression of the low temperature cone structure was found and just a helical state was observed above 4 GPa. This state is incommensurate in the temperature range TL < T < TN and becomes commensurate below TL. At T = 7 K, the qz component evolves towards ¼ c* value at 8.7 GPa. The Néel temperature decreases to 108 K with a pressure increase up to 8.7 GPa with a pressure coefficient dTN/dP ≈ −2.2 K/GPa, while the lock-in transition temperature exhibits opposite behavior and grows up to about 50 K with a coefficient of dTL/dP ≈ 3.4 K/GPa. The magnetic P-T phase diagram of Ho is constructed. The compression of Ho lattice at T = 7 K is nearly isotropic, as found from about the same compressibilities of the a and c axes.