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Europium ð‘-axis ferromagnetism in Euâ¢(Co1−ð‘¥â¢Nið‘¥)2−ð‘¦â¢As2: A single-crystal neutron diffraction study

by Yan Wu
Publication Type
Journal
Journal Name
Physical Review B
Publication Date
Volume
109
Issue
17

We report neutron diffraction results for the body-centered-tetragonal series Euâ¢(Co1−ð‘¥â¢Nið‘¥)2−ð‘¦â¢As2, ð‘¥=0.10, 0.20, 0.42, and 0.82, ð‘¦â‰¤0.10, that detail changes to the magnetic ordering with nominal hole doping. We report the antiferromagnetic (AFM) propagation vectors, magnetic transition temperatures, and the ordered magnetic moments. We find a nonmonotonic change of the AFM propagation vector with ð‘¥, with a minimum occurring at the tetragonal to collapsed-tetragonal phase crossover. For ð‘¥=0.10 and 0.82 we find ð‘-axis helix ordering of the Eu magnetic moments (spins) similar to ð‘¥=0 and 1, with the spins oriented within the ðšð›-plane. For ð‘¥=0.20 and 0.42 we find higher-temperature ð‘-axis ferromagnetic (FM) order and lower-temperature ð‘-axis cone order. Using the extinction conditions for the space group, we discovered that the Eu spins are ordered in the higher-temperature ð‘-axis FM phase for intermediate values of ð‘¥, contrary to a previous report suggesting only Co/Ni spin ordering. Although we cannot directly confirm that the Co/Ni spins are also ordered, we suggest that ð‘-axis itinerant-FM ordering of the Co/Ni spins could provide a molecular field that drives FM ordering of the Eu spins, which in turn provides the anisotropy for the lower-temperature ð‘-axis cone order.