High pressure study on quadrupolar and magnetic order in HoBC by means of neutron single-crystal diffraction

Yamauchi, Hiroki   ; Osakabe, Toyotaka  ; Matsuoka, Eiichi*; Onodera, Hideya*

HoBC shows a magnetic order at = 5.8 K with an incommensurate structure and undergoes a first order transition towards a commensurate phase at = 4.5 K. The magnetic structure below is basically described by the propagation vectors of = (1, 0, 0) and = (0, 1, 1/2) for the antiferromagnetic (AFM) alignment in the c-plane and the orthogonal arrangement along the -axis that is attributed to the competitive coexistence of the underlying antiferroquadrupolar (AFQ) order with the AFM order. Since the pressure directly acts on the quadrupolar order coupled with the lattice, the high-pressure neutron experiments allows us to study the significant competition state under systematic changes from the microscopic point of view. Thus, we carried out the neutron single-crystal diffraction experiments under high pressure to investigate the pressure effect on the competitive AFQ + AFM order in HoBC through the alteration of the magnetic structures with and . The high-pressure experiments revealed that the AFQ ordering in HoBC was extremely pressure sensitive and suppressed by pressure below 4 GPa whereas the pressure enhanced the AFM interactions up to 10 GPa. Above 4 GPa, we found the new pressure-induced phases, phase AFM1 and AFM2, where HoBC transformed into the magnetic structures represented by + ( = (, , 0), ) and , respectively.