Flat-band tuning and emergent itinerant magnetism in Sr(CoPd)As
Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine
Significance Modulating electronic correlation by tuning flat-band instability is a central study of quantum materials. In this work, we demonstrate that substituting a tiny amount (2%) of nonmagnetic Pd into, an otherwise Pauli paramagnetic compound, induces long-range magnetic order. This surprising result arises from flat-band instability: Electron doping from Pd substitution shifts a nearly dispersionless Co-derived flat band close to the Fermi energy, enhancing magnetic instability. Our combined experimental and theoretical study reveals a helical magnetic order at low doping, which evolves into a complex ferromagnetic state at higher Pd levels. These findings provide compelling evidence for the critical role of flat bands in driving emergent magnetism in itinerant electron systems. executive-summary The interplay between magnetism and flat-band (FB) instability is a central theme in quantum materials research. A striking example is the emergence of magnetic order in a nominally nonmagnetic compound when a flat band is tuned near the Fermi energy (). In this study, we investigate this phenomenon in the Pauli paramagnet, where an FB associated with Coorbitals lies close to. Remarkably, a minute substitution of the nonmagnetic element Pd onto the Co site (2%) induces antiferromagnetic order with a transition temperature as high asK. Temperature- and magnetic-field-dependent magnetic and transport measurements, complemented by zero-field neutron diffraction, reveal a helica
Abstract
Significance Modulating electronic correlation by tuning flat-band instability is a central study of quantum materials. In this work, we demonstrate that substituting a tiny amount (2%) of nonmagnetic Pd into, an otherwise Pauli paramagnetic compound, induces long-range magnetic order. This surprising result arises from flat-band instability: Electron doping from Pd substitution shifts a nearly dispersionless Co-derived flat band close to the Fermi energy, enhancing magnetic instability. Our combined experimental and theoretical study reveals a helical magnetic order at low doping, which evolves into a complex ferromagnetic state at higher Pd levels. These findings provide compelling evidence for the critical role of flat bands in driving emergent magnetism in itinerant electron systems. executive-summary The interplay between magnetism and flat-band (FB) instability is a central theme in quantum materials research. A striking example is the emergence of magnetic order in a nominally nonmagnetic compound when a flat band is tuned near the Fermi energy (). In this study, we investigate this phenomenon in the Pauli paramagnet, where an FB associated with Coorbitals lies close to. Remarkably, a minute substitution of the nonmagnetic element Pd onto the Co site (2%) induces antiferromagnetic order with a transition temperature as high asK. Temperature- and magnetic-field-dependent magnetic and transport measurements, complemented by zero-field neutron diffraction, reveal a helical magnetic order forin Sr(CoPd)As, transitioning to a complex ferromagnetic state at higher Pd concentrations. Spectroscopic evidence and theoretical band structure calculations demonstrate that electron doping shifts the flat band closer to, significantly enhancing the Stoner parameter. This enhancement drives a strong ferromagnetic instability, leading to helical magnetic ordering dominated by in-plane ferromagnetic interactions. The emergence of robust magnetic ordering through substitution with nonmagnetic elements is a unique phenomenon that underscores the pivotal role of flat-band instability in tuning magnetism in itinerant systems.