New aspects of the magnetic excitations in HoCo2

Abstract

We have obtained new results about the magnetic excitation spectrum of HoCo2 using inelastic neutron scattering. It has been possible to observe at 6 K a well-defined cobalt excitation mode up to 14 THz. The application of a magnetic field along the easy magnetization axis has revealed the longitudinal character of the excitation at 2 THz observed at 6 K. New modes below and above the rotation temperature have been measured. These results have been analyzed in a Green's-function formalism using the random-phase approximation to determine the crystalline electric field (CEF) and the exchange parameters. Despite the use of an extra quadrupolar term for the crystalline field it has not been possible to get a satisfactory agreement fN' the dispersion curves obtained, together with the macroscopic measurements.However, the values obtained 8' =0.2983 K and x = W.4839 for the CEF parameters are in agreement with those determined by other authors. The exchange parameters have been determined as JHO Ho 0 +0 0005 THz JHO g 0 07 THz and Jgo go 9 TH z. The main discrepancy concerns JH, |-,which may be determined from the gap of the cobalt mode or from the molecular field when the CEF transition levels are fitted regardless of the cobalt mode. The discrepancy suggests that it might be necessary to take into account a mixture of 3d and 4f magnetism at the very level of the exchange mechanism, including the itinerant character of the 3d electrons.

Investigation of the Direction of Spontaneous Magnetisation at 0 K in HoCo2 and TmFe2

“…The parameters for HoCo 2 and TmFe 2 derived from published data. a: Gignou et al [9], b: Aubert et al [10], c: Castets and Gignoux [11], d: Germano and Butera [12], e: Martin et al [13] derived values of B 4 and B 6 from the data of Atzimony et al [14], f: Yanovsky et al [15], g and h derived by Bleaney [18] from Rhyne and Koon [16] and Koon and Rhyne [17], i: Bleaney [18].…”

Spin-Orbit Exciton in a Honeycomb Lattice Magnet CoTiO$_3$: Revealing Link Between Rare Earth and Transition Metal Magnetism

“…Instead, dynamics of the higher energy multiplets become strongly dependent on what happens in the low energy sector, and vice versa. Direct evidence for this is a strong renormalization of the higher energy SO excitations across magnetic ordering that has been observed in some rare-earth systems [17][18][19][20][21][22] . These observations can be only explained through a multi-level theory 23,24 where ground and excited multiplets are considered simultaneously.…”

he Direction of Spontaneous Magnetisation of Lanthanide Ions at a Site of Cubic Symmetry

“…A small increase in R will causes the compound to magnetise along the < 100> axis. How ever, the parameters given by Aubert et al (1978) place the compound just inside the reorientation area and those published by Castet et al (1982) place the compound on the other (< 100> ) side of the boundary.…”