Helical magnetic order and Fermi surface nesting in non-centrosymmetric ScFeGe

TL;DR

This paper studies non-centrosymmetric ScFeGe, revealing its helical magnetic order linked to Fermi surface nesting, and explores how in-plane magnetic fields influence its magnetic and electronic properties.

Contribution

It provides the first detailed experimental and theoretical analysis of the magnetic structure and Fermi surface nesting in ScFeGe, highlighting its Fermi surface driven magnetic transition.

Findings

Helical magnetic order with wavevector (0 0 0.193) below 36 K.

Fermi surface nesting correlates with magnetic transition.

Metamagnetic transition at approximately 6.7 T in in-plane magnetic fields.

Abstract

An investigation of the structural, magnetic, thermodynamic, and charge transport properties of non-centrosymmetric hexagonal ScFeGe reveals it to be an anisotropic metal with a transition to a weak itinerant incommensurate helimagnetic state below $T_N = 36$ K. Neutron diffraction measurements discovered a temperature and field independent helical wavevector \textbf{\textit{k}} = (0 0 0.193) with magnetic moments of 0.53 $\mu_{B}$ per formula unit confined to the {\it ab}-plane. Density functional theory calculations are consistent with these measurements and find several bands that cross the Fermi level along the {\it c}-axis with a nearly degenerate set of flat bands just above the Fermi energy. The anisotropy found in the electrical transport is reflected in the calculated Fermi surface, which consists of several warped flat sheets along the $c$-axis with two regions of significant nesting, one of which has a wavevector that closely matches that found in the neutron diffraction. The electronic structure calculations, along with a strong anomaly in the {\it c}-axis conductivity at $T_N$, signal a Fermi surface driven magnetic transition, similar to that found in spin density wave materials. Magnetic fields applied in the {\it ab}-plane result in a metamagnetic transition with a threshold field of $\approx$ 6.7 T along with a sharp, strongly temperature dependent, discontinuity and a change in sign of the magnetoresistance for in-plane currents. Thus, ScFeGe is an ideal system to investigate the effect of in-plane magnetic fields on an easy-plane magnetic system, where the relative strength of the magnetic interactions and anisotropies determine the topology and magnetic structure.