Anisotropic magnetic field dependence of the magnetization dynamics in $\mathrm{U}{\mathrm{Pd}}_2{\mathrm{Al}}_3$

The magnetization dynamics of the magnetic superconductor $\mathrm{U}{\mathrm{Pd}}_2{\mathrm{Al}}_3$ has been investigated by inelastic neutron scattering in the normal and superconducting, antiferromagnetically ordered state under a magnetic field applied parallel to the hexagonal $c$ axis. Within the available resolution, the dynamic response below $2.5\mathrm{meV}$ is insensitive to the applied field on the scale of the field dependence reported by E. Blackburn et al. [Phys. Rev. B 74, 024406 (2006)] in which the field was applied in the basal plane. Our results support that the previously reported field dependent quasielastic contribution is related to the dynamics of the rotation of the magnetic moment. The changes observed in the inelastic part of the excitation spectrum are consistent with those expected from spin-wave theory. Interestingly, the anisotropic field dependence of the normal-state response may be correlated with the superconducting properties of this material.

Figure 1

(Color online) The dynamic response of $\mathrm{U}{\mathrm{Pd}}_2{\mathrm{Al}}_3$ at $T=2.5\mathrm{K}$ at the antiferromagnetic zone center (0 0 0.5) for energies $\Delta E⩽2.5\mathrm{meV}$ as measured by inelastic neutron scattering on IN14 with $k_f=1.15\mathrm{\AA }$. Left-hand side panels: When the magnetic field is parallel to the $b$ axis, the low-energy response $\Delta E⩽0.3\mathrm{meV}$ increases in field, whereas the inelastic scattering intensity is reduced between 0.5 and $1.5\mathrm{meV}$. Data taken from Ref. 5. Right-hand side panels: When the magnetic field is parallel to the $c$ axis, no such changes are observed.

Figure 2

(Color online) The dynamic response of $\mathrm{U}{\mathrm{Pd}}_2{\mathrm{Al}}_3$ at $T=0.3\mathrm{K}$ at the antiferromagnetic zone center (0 0 0.5) for energies $\Delta E⩽2.5\mathrm{meV}$ as measured by inelastic neutron scattering on IN14 with $k_f=1.15\mathrm{\AA }$ at zero field and as well as with magnetic fields $B>B_{c2}$ applied along the $b$ axis (left-hand side, $B_{c2}^b=3.3\mathrm{T}$) and the $c$ axis (right-hand side, $B_{c2}^c=3.7\mathrm{T}$). The solid line is a smooth fit to the $2.5\mathrm{K}$ data from Fig. 1 at similar fields, scaled by a Bose temperature factor. Three contributions marked by arrows are discussed in the text.