Evidence for Emergent Kagome Spin Configuration with Concomitant Transverse and Longitudinal Spin-Glass Freezing in the Chemically Ordered M-type Hexaferrite BaFe12O19

Abstract: Frustration effects in magnetic systems have traditionally been investigated considering pre-existing site-disorder or lattice geometry of the high-temperature paramagnetic phase. We present here evidence for emergence of geometrical frustration as a function of temperature due to spin canting in the long-range ordered (LRO) ferrimagnetic (FMI) phase of BaFe12O19 (BFO), an M-type hexaferrite of enormous technological applications. Results of neutron scattering and magnetic susceptibility studies on BFO are presented to show for the first time the emergence of highly degenerate kagome spin configuration for the basal plane spin component of BFO with concomitant freezing of transverse and longitudinal components of the spins leading to two spin-glass transitions in coexistence with the LRO FMI phase. Our results mimic the theoretical predictions for concentrated Heisenberg systems even though the source of frustration in BFO is the geometry of the lattice and not site-disorder. We believe that our findings will stimulate theoretical studies to unravel the physics of spin-glass transitions in LRO systems due to emergent geometrical frustration, an aspect that has remained unexplored so far. We also believe that this work will encourage further experimental studies in search of low temperature spin-glass transition(s) in LRO phases of various hexaferrites and even other LRO magnetic compounds with spins arranged on triangular, pyrochlore and spinel lattices without any substitutional disorder.