Speaker
Description
The rare earth boride HoB$_{12}$ crystallizes in the fcc structure and shows antiferromagntic order at $T_N = 7.4$ K. The ordering is described by an incommensurate ordering vector $Q_{af}$ = ($0.47,0.47,0.47$) [1]. In a magnetic field HoB$_{12}$ shows a complex phase diagram where nine different magnetic phases can be distinguished [2].
Here the phase diagram is discussed in the light of our recent determination of the single ion anisotropy using neutron scattering methods. The single ion anisotropy favors the alignment of the rare earth moment along the ($111$) directions. In the Ho-ion ground state we find an effective moment of $6$ $\mu_B$ in good agreement to magnetization data. Compared to the ordering temperature, excited crystal field states are much higher [3] and can be neglected here. The dipolar anisotropy is also relevant because the moment is quite large. We argue that the incommensurate ordering is caused by the dipolar interactions. A numerical spin wave calculation shows that the $0.5$ meV gap in the dispersion must also be caused by the dipolar interaction. The different phases observed in magnetic field result from the competition of the single crystal anisotropy and dynamic charge stripes [2]. It selects specific directions of the ordering vector without altering its absolute value. Selection rules will be given and compared to experimental data obtained from neutron diffraction.
Acknowledgements
This work was supported by projects DAAD-SAS-2023-02, APVV-23-0226, VEGA 2/0034/24.
References
[1] K. Siemensmeyer et al., “Magnetic Properties of the Frustrated fcc – Antiferromagnet HoB12 Above and Below T N,” Journal of Low Temperature Physics, vol. 146, no. 5–6. Springer Science and Business Media LLC, pp. 581–605, Jan. 25, 2007. https://doi.org/10.1007/s10909-006-9287-4
[2] K. Krasikov et al., “Suppression of indirect exchange and symmetry breaking in the antiferromagnetic metal HoB12 with dynamic charge stripes”, Physical Review B, vol. 102, no. 21. American Physical Society (APS), Dec. 28, 2020. https://doi.org/10.1103/physrevb.102.214435
[3] B. Z. Malkin et al., “Crystal-field potential and short-range order effects in inelastic neutron scattering, magnetization, and heat capacity of the cage-glass compound HoB12”, Physical Review B, vol. 104, no. 13. American Physical Society (APS), Oct. 29, 2021. https://doi.org/10.1103/physrevb.104.134436
