Quantum percolation phase transition and magneto-electric dipole glass in hexagonal ferrites

Abstract

Hexagonal ferrites do not only have enormous commercial impact (£2 billion/year in sales) due to applications that include ultra-high density memories, credit card stripes, magnetic bar codes, small motors and low-loss microwave devices, they also have fascinating magnetic and ferroelectric quantum properties at low temperatures. Here we report the results of tuning the magnetic ordering temperature in PbFe${}_{12-x}$Ga${}_x$O${}_{19}$ to zero by chemical substitution $x$. The phase transition boundary is found to vary as $T_N\sim (1-x/x_c{)}^{2/3}$ with $x_c$ very close to the calculated spin percolation threshold which we determine by Monte Carlo simulations, indicating that the zero-temperature phase transition is geometrically driven. We find that this produces a form of compositionally-tuned, insulating, ferrimagnetic quantum criticality. Close to the zero temperature phase transition we observe the emergence of an electric-dipole glass induced by magneto-electric coupling. The strong frequency behaviour of the glass freezing temperature $T_m$ has a Vogel-Fulcher dependence with $T_m$ finite, or suppressed below zero in the zero frequency limit, depending on composition $x$. These quantum-mechanical properties, along with the multiplicity of low-lying modes near to the zero-temperature phase transition, are likely to greatly extend applications of hexaferrites into the realm of quantum and cryogenic technologies.

arXiv comment17 pages. Final version as published

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Cited by in corpus (5)

• Different dielectric, magnetic, and magnetodielectric mechanisms in M-type BaFe12O19 hexaferrite regulated by doping Ga3+ and In3+ cations
• Evidence for coexistence of spin-glass and ferrimagnetic phases in BaFe12O19 due to basal plane freezing
• Phase boundary near a magnetic percolation transition
• Quantum Critical Points in Ferroelectric Relaxors: Stuffed Tungsten Bronze K3Li2Ta5O15 and Lead Pyrochlore (Pb2Nb2O7)
• Magnetic properties of diluted hexaferrites