Magnetism of YMn6Sn6 and DyMn6Ge6: Single-crystal Study
The magnetic properties of YMn6Sn6 and DyMn6Ge6, which crystallize in the hexagonal HfFe6Ge6-type of structure, have been studied on single crystals that have been prepared in an Sn flux and In flux, respectively. The compounds order antiferromagnetically at about 330 K and 450 K and exhibit very complex magnetic properties in the magnetically ordered state. The evolution of the magnetization in the ordered state has been investigated in the temperature region from 2 to 550 K and magnetic field up to 14 T.
Competing magnetic phases and fluctuation-driven scalar spin chirality in the kagome metal YMn6Sn6.
Identification, understanding, and manipulation of novel magnetic textures are essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic field are subject to intense investigation. Here, we study the kagome-net magnet YMn6Sn6 by magnetometry, transport, and neutron diffraction measurements combined with first-principles calculations. We identify a number of nontrivial magnetic phases, explain their microscopic nature, and demonstrate that one of them hosts a large topological Hall effect (THE). We propose a previously unidentified fluctuation-driven mechanism, which leads to the THE at elevated temperatures. This interesting physics comes from parametrically frustrated interplanar exchange interactions that trigger strong magnetic fluctuations. Our results pave a path to chiral spin textures, promising for novel spintronics.
Magnetic structures and interactions in erbium
The magnetic structures in a single crystal of isotopically enriched erbium have been studied using a high-resolution neutron diffraction technique at the HFIR reactor at Oak Ridge National Laboratory. In addition, these structures have been examined by mean-field calculations, in which the primary interactions were derived from magnetization and spin-wave measurements. The agreement between theory and experiment is generally very good. At intermediate temperatures, the structure is based on an elliptical cycloid in the a-c plane, and blocks of moments with alternating positive and negative components in the c-direction give rise to a series of commensurable structures in the manner proposed by Gibbs and co-workers (1986). These structures are, however, distorted by two-ion couplings of trigonal symmetry, which reflect the different orientation of the two HCP sublattices and have a magnitude which is a substantial fraction of the isotropic exchange interaction. The result is a wobbling cycloid, in which there is an oscillating moment in the b-direction whose period differs from that of the basic cycloidal structure. In the low-temperature cone phase, the moments bunch around alternating a-directions in a pattern with trigonal rather than hexagonal symmetry. Some further consequences of the trigonal couplings on the low-symmetry magnetic structures in erbium and holmium are discussed.