Synthesis and study of the chiral magnetic system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>EuIr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">P</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>
D. G. Franco, C. Geibel
Abstract
Chiral materials, where no improper symmetry operations such as inversion are present, are systems prone to the appearance of a skyrmion lattice. Recently it has been shown theoretically that not only ferromagnets (FMs) but also antiferromagnets (AFMs) can host such kind of phases. In this work we study a new candidate for AFM skyrmions, ${\mathrm{EuIr}}_{2}{\mathrm{P}}_{2}$, by means of magnetization and specific heat measurements on poly and single crystals. X-ray diffraction confirms a trigonal chiral crystal structure, where europium ions form helices along the $c$ direction. In spite of predominantly FM interactions, ${\mathrm{Eu}}^{2+}$ ions order antiferromagnetically at ${T}_{{N}_{1}}=5$ K in what seems to be an incommensurate amplitude-modulated magnetic state where the moments are oriented mainly along the $c$ direction. A second magnetic transition takes place at ${T}_{{N}_{2}}=2.9$ K, involving the ordering of an in-plane component of the Eu moment likely resulting in an equal-moment structure. Specific heat data show a tail above ${T}_{{N}_{1}}$. Accordingly the magnetic entropy at ${T}_{{N}_{1}}$ is strongly reduced in comparison to the expected $Rln8$ value. This evidences a significant amount of frustration. A simple analysis based on a Heisenberg model indicates that the observed properties imply the presence of several relevant interactions, with competing FM and AFM ones resulting in frustration. Thus ${\mathrm{EuIr}}_{2}{\mathrm{P}}_{2}$ is a new interesting magnetic system, where chirality and frustration might result in unconventional magnetic textures.