arXiv subjects

Mason Christiansen

Publications and source records attributed to Mason Christiansen.

3 recordsLinked to original sources

arXiv2026

Experimental demonstration of dual-polarization nonreciprocal thermal emission at moderate magnetic fields

Conventional thermal emitters obey Kirchhoff's law of thermal radiation, which requires emissivity and absorptivity to be equal at each wavelength, angle, and polarization. This in turn places a fundamental limit on a range of radiative energy technologies as well as heat transfer. This constraint can however be overcome using magneto-optic semiconductors, which break Lorentz reciprocity under an applied magnetic field. However, in most prior experimental demonstrations, nonreciprocity has been restricted to TM polarization, since the electric field of TE-polarized light is parallel to the applied magnetic field. Here, we experimentally demonstrate nonreciprocal absorption in both polarizations at the same wavelengths and angles from a single structure, wherein a germanium Mie-resonant metasurface on a doped InAs layer scatters TE-polarized light into near fields with components perpendicular to the magnetic field, allowing the magneto-optic response of the InAs to act on them. Under a 0.48 T field from a permanent Halbach array, this structure exhibits a difference in absorptivity between $+B$ and $-B$ of 0.035 in both TE and TM polarization at 16.6 $μ$m. Our approach shows that the magneto-optic response of a planar semiconductor and the resonances of a dielectric metasurface can be designed together, offering a potential route to dual-polarization nonreciprocity at fields available from permanent magnets for emerging energy and heat transfer technologies.

physics.optics↗

arXiv2026

Nonreciprocal magneto-optic beam steering of thermal emission

Conventional thermal emitters obey Kirchhoff's law of thermal radiation, which ties absorptivity to emissivity and places a fundamental limit on a range of radiative energy technologies and sensing systems. This constraint can be overcome using magneto-optic materials, which exhibit nonreciprocal thermal emission under an applied magnetic field. While the spectral nonreciprocity of magneto-optic devices has been explored theoretically and experimentally, nonreciprocal control over the direction of thermal emission has received far less attention. Here, we propose and numerically demonstrate nonreciprocal beam steering of thermal emission, wherein an applied magnetic field lifts the degeneracy between guided modes at +/- kx, enabling asymmetric and tunable directional thermal emission. We highlight a III-V semiconductor photonic structure operating at 24.5 um, a wavelength with few laser sources. This structure exhibits a nonreciprocity greater than 0.5 between +/- 75 degrees at 50 mT, a peak emissivity asymmetry over 0.6 at 150 mT, and 22 degrees of beam steering between 0 and 1 T. Our approach provides a solid-state means of steering a thermal beam, offering a potential route to magnetically controlled beam scanning of incandescent sources.

physics.optics↗

arXiv2021

Superparamagnetic dynamics and blocking transition in Fe$_3$O$_4$ nanoparticles probed by vibrating sample magnetometry and muon spin relaxation

The magnetic properties of Fe$_3$O$_4$ nanoparticle assemblies have been investigated in detail through a combination of vibrating sample magnetometry and muon spin relaxation ($μ$SR) techniques. Two samples with average particle sizes of 5 nm and 20 nm, respectively, were studied. For both samples, the magnetometry and $μ$SR results exhibit clear signatures of the superparmagnetic state at high temperature and the magnetically blocked state at low temperature. The $μ$SR data demonstrate that the transition from the superparamagnetic to the blocked state occurs gradually throughout the sample volume over a broad temperature range due to the finite particle size distribution of each sample. The transition occurs between approximately 3 K and 45 K for the 5 nm sample and 150 K and 300 K for the 20 nm sample. The magnetometry and $μ$SR data are further analyzed to yield estimates of microscopic magnetic parameters including the nanoparticle spin-flip activation energy $E_A$, magnetic anisotropy $K$, and intrinsic nanoparticle spin reversal attempt time $τ_0$. These results highlight the complementary information about magnetic nanoparticles that can be obtained by bulk magnetic probes such as magnetometry and local magnetic probes such as $μ$SR.

cond-mat.mes-hall↗