Quantum materials near electronic or magnetic phase boundaries exhibit enhanced tunability, as their emergent properties become highly sensitive to external perturbations. Here, we demonstrate precise control of ferromagnetism in a SrRuO3 ultrathin film, where a high density of states (DOS), arising from low-dimensional quantum states, places the system at the crossover between a non-magnetic and bulk ferromagnetic state. Using spin- and angle-resolved photoemission spectroscopy (SRPES/ARPES), transport measurements, and theoretical calculations, we systematically tune the Fermi level via electron doping across the high-DOS point. We directly visualize the spin-split band structure and reveal its influence on both magnetic and transport properties. Our findings provide compelling evidence that magnetism can be engineered through DOS control at a phase crossover, establishing a pathway for the rational design of tunable quantum materials.
@article{arxiv.2512.09320,
title = {Low-dimensionality-induced tunable ferromagnetism in SrRuO$_3$ ultrathin films},
author = {Jinyoung Kim and Minjae Kim and Donghan Kim and Sungsoo Hahn and Younsik Kim and Minsoo Kim and Byungmin Sohn and Changyoung Kim},
journal= {arXiv preprint arXiv:2512.09320},
year = {2026}
}