Title: Tuning the intrinsic anomalous Hall effect from large to zero in the two ferromagnetic states of the layered SmMn2Ge2

Abstract: The intrinsic anomalous Hall conductivity in a ferromagnetic metal is completely determined by its band structure. Since the spin orientation direction is an important band structure tuning parameter, it is highly desirable to study the anomalous Hall effect in a system with multiple spin reorientation transitions. We study a layered tetragonal room temperature ferromagnet SmMn2Ge2, which gives us the opportunity to measure magneto-transport properties where the long c-axis and the short a-axis can both be magnetically easy axes depending on the temperature range we choose. We show a moderately large completely intrinsic anomalous Hall conductivity (AHC) up to room temperature when the crystal is magnetized along c-axis. Interestingly, the AHC can be tuned to completely extrinsic with extremely large values when the crystal is magnetized along a-axis irrespective of whether the a-axis is magnetically easy or hard axis. The first principles calculations show that nodal line states originate from Mn-d orbitals just below the Fermi energy (EF) in the electronic band structure when the spins are oriented along the c-axis. Intrinsic AHC originates form the Berry curvature effect of the gapped nodal lines in the presence of spin-orbit coupling. AHC almost vanishes when the spins are aligned along the a-axis because nodal line states shift above EF and become unoccupied states.