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 PbFe12-xGaxO19 to zero by chemical substitution x. The phase transition boundary is found to vary as TN~(1 - x/xc)2/3 with xc 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 unique 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 Tm has a Vogel-Fulcher dependence with Tm finite, or suppressed below zero in the zero frequency limit, depending on 2 of 18 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.
Citation
Rowley , S E , Vojta , T , Jones , A , Guo , W , Oliveira , J , Morrison , F D , Lindfield , N , Baggio-Saitovitch , E , Watts , B E & Scott , J F 2017 , ' Quantum percolation phase transition and magneto-electric dipole glass in hexagonal ferrites ' , Physical Review. B, Condensed matter and materials physics , vol. 96 , no. 2 , 020407(R) . https://doi.org/10.1103/PhysRevB.96.020407
Publication
Physical Review. B, Condensed matter and materials physics
Status
Peer reviewed
ISSN
1098-0121Type
Journal article
Description
SER and EBS acknowledge support from a CONFAP Newton grant. T.V. acknowledges support from the NSF under Grant No. DMR-1506152.Collections
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