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arXiv · 2509.14716

Detection of ferroic octupole ordering in $d$-wave altermagnetic rutile-type compounds

Masaichiro Mizumaki·Norimasa Sasabe·Takayuki Uozumi·Rikuto Oiwa·Hiroaki Kusunose
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Abstract

We propose that X-ray absorption and emission magnetic circular dichroism (XAS-MCD and XES-MCD) are promising measurements to directly detect ferroic higher-rank multipoles as candidate order parameters in altermagnets. Using the sum rules for XES-MCD and connecting them to multipole language, we demonstrate that the expectation value of the magnetic octupole moment is finite in the $d$-wave altermagnetic candidate rutile-type compounds TF$_2$ (T=transition metal). We also perform spectral calculations of XAS-MCD and XES-MCD based on an effective model with a full multiplet approach. While the intensity of the XAS-MCD spectra vanishes, the XES-MCD spectra exhibit finite intensity, whose spectrum becomes opposite by inverting the N\`eel vector. These results clearly indicate ferroic magnetic octupole order in these compounds.

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Masaichiro Mizumaki, Norimasa Sasabe, Takayuki Uozumi, Rikuto Oiwa, Hiroaki Kusunose. 2025-09-18. Detection of ferroic octupole ordering in $d$-wave altermagnetic rutile-type compounds. https://doi.org/10.1103/d9r5-8hy8

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