Field Induced Modulated State in the Ferromagnet PrPtAl

Data supporting the paper: O'Neill, C. D., Abdul-Jabbar, G., Wermeille, D., Bourges, P., Kruger, F., & Huxley, A. D. (Accepted/In press). "A field induced modulated state in the ferromagnet PrPtAl". Physical Review Letters. # ABSTRACT # The theory of quantum order-by-disorder (QOBD) explains the formation of modulated magnetic states at the boundary between ferromagnetism and paramagnetism in zero field. PrPtAl has been argued to provide an archetype for this. Here, we report the phase diagram in magnetic field, applied along both the easy $a$-axis and hard $b$-axis. For field aligned to the $b$-axis, we find that the magnetic transition temperatures are suppressed and at low temperature there is a single modulated fan state, separating an easy $a$-axis ferromagnetic state from a field polarised state. This fan state is well explained with the QOBD theory in the presence of anisotropy and field. Experimental evidence supporting the QOBD explanation is provided by the large increase in the $T^2$ coefficient of the resistivity and direct detection of enhanced magnetic fluctuations with inelastic neutron scattering, across the field range spanned by the fan state. This shows that the QOBD mechanism can explain field induced modulated states that persist to very low temperature.O'Neill, Christopher; Huxley, Andrew. (2021). Field Induced Modulated State in the Ferromagnet PrPtAl, [dataset]. University of Edinburgh. School of Physics and Astronomy. https://doi.org/10.7488/ds/3024

Is it possible to create a perfect fractional vortex beam?

Laguerre-Gaussian beams of integer azimuthal index satisfy the fundamental principle of quantization of orbital angular momentum. Here, we consider light-induced orbiting of a trapped microparticle as a probe of the local orbital angular momentum density in both integer- and fractional-index perfect vortex beams. Simulations suggest that the distribution and the corresponding light-induced motion of the particle, may be uniform in beams with integer azimuthal index but fundamentally this cannot be achieved in beams with fractional index. We experimentally verify these predictions by light-induced trapping and rotation of individual microparticles in fractional index beams where we distribute the phase dislocations around the annular profile.Publisher PDFPeer reviewe