Condensed Matter Seminar: Prof. Nirmal Ghimire, George Mason University


Location: 184 Nieuwland Science Hall (View on map )

Magnetic and electronic topological states in the kagome-net magnet YMn6Sn6

Prof. Nirmal Ghimire
Assistant Professor
Physics & Astronomy Department
George Mason University

Identification, understanding, and manipulation of novel electronic and magnetic states is essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest an interplay of magnetism and electronic topology are subject to intense investigation; kagome net magnets are prime candidates1. In this talk I will present the magnetotransport signatures of the magnetic and electronic topological states in the kagome-net magnet YMn6Sn6. YMn6Sn6 crystallizes in the hexagonal space group P6/mmm with Mn atoms forming a kagome net in the basal plane. The material orders antiferromagnetically at 345 K and quickly transitions into an incommensurate spiral below 333 K. For a magnetic field applied in the ab-plane, a series of competing phases namely distorted spiral (DS), transverse conical spiral (TCS) and Fan-like (FL) phases are stabilized before polarizing to the forced ferromagnetic (FF) state2,3. In this field orientation, this compound shows an enigmatic topological Hall effect near room temperature within the TCS phase, which we attribute to a new fluctuation-driven mechanism2.  In addition to this THE,  YMn6Snshows two other intriguing magnetotransport features at lower temperatures: an anisotropic magnetoresistance drop due to a magnetization-driven topological phase transition (Lifshitz transition), and an interlayer MR due to the charge-spin coupling associated with the magnetic texture in the FL phase in absence of a strong spin orbit coupling4. These phenomena provide a unique view into the magnetic and electronic topological states and their interplay in YMn6Sn6.


1. Ghimire and  Mazin., Nature Materials 19, 130 (2020)
2. Ghimire et al., Science Advances 2020; 6 : eabe2680 (2020)
3. Dally et al., Phys. Rev. B 103, 094413 (2021)
4. Siegfried et al, Preprint: Res. Square, DOI 10.21203/ (2021)