High-pressure magnetization measurements for single-element heavy lanthanide metal magnets using SQUID and diamond anvil cell

Abstract Heavy lanthanide ferromagnetic metals, such as gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), and thulium (Tm) have a hexagonal close-packed (hcp) crystal structure at ambient pressure. Under hydrostatic pressure, the hcp structure transforms into a Samarium (Sm)-type structure, which leads to further transitions into double hcp (dhcp) and face-centered-cubic (fcc) structures. The three types of hexagonal stacking layers are labeled as A, B, and C, and the change in the unit cell for the above structural transformation is represented as ABA (hcp) → ABABCBCACA (Sm-type) → ABACA (dhcp) → ABCA (fcc). This structural transformation is characterized by the insertion or extraction of stacking faults in the hexagonal stacking structures. Subsequently, magnetic ordering is created with magnetic interaction between the 4 f moments mediated by conduction electrons, which can be modified by compression. This series of precise magnetic measurements requires a pressure range of at least 10 GPa, such that the uses of both a diamond anvil cell to obtain the pressure and a superconducting quantum interference device (SQUID) magnetometer covering wide temperature and direct current (dc) magnetic field ranges are required. This review presents the results of dc and alternating current (ac) magnetization measurements for Sm and Gd–Tm. Their results are compared with the results of electrical resistance and unit cell volume, and qualitatively discussed with the density of states at the Fermi energy.