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Schlagwörter:
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Zusammenfassung:
In divalent Eu systems, the 4f local moment has a pure spin state J = S
= 7/2. Although the absence of orbital moment precludes crystal electric
field effects, we report a sizable magnetic anisotropy in single
crystals of EuRh2Si2. We observed a surprisingly complex magnetic
behavior with three successive phase transitions. The Eu2+ moments order
in a probably amplitude-modulated structure below 24.5 K, undergoing a
further transition to a structure that is possibly of the equal-moment
type, and a first order transition at lower temperatures, presumably
into a spin spiral structure. The sharp metamagnetic transition observed
at low fields applied perpendicular to the hard axis is consistent with
a change from a spiral to a fan structure. These magnetic structures are
presumably formed by ferromagnetic planes perpendicular to the c axis,
stacked antiferromagnetically along c but not of type I, at least just
below the ordering temperature. Since EuRh2Si2 is isoelectronic and
isostructural to EuFe2As2 at room temperature, our results are also
relevant for the complex Eu-magnetism observed there, especially for the
transition from an antiferromagnetic to a ferromagnetic state observed
in EuFe2P2 upon substituting As by P.