R. D. Johnson

Non-ferroelectric nature of the conductance hysteresis in CH3NH3PbI3 perovskite-based photovoltaic devices

We present measurements of conductance hysteresis on CH3NH3PbI3 perovskite thin films, performed using the double-wave method, in order to investigate the possibility of a ferroelectric response. A strong frequency dependence of the hysteresis is observed in the range of 0.1 Hz to 150 Hz, with a hysteretic charge density in excess of 1000 μC cm−2 at frequencies below 0.4 Hz—a behaviour uncharacteristic of a ferroelectric response. We show that the observed hysteretic conductance, as well as the presence of a double arc in the impedance spectroscopy, can be fully explained by the migration of mobile ions under bias on a timescale of seconds. Our measurements place an upper limit of ≈1 μC cm−2 on any intrinsic frequency-independent polarisation, ruling out ferroelectricity as the main cause of current-voltage hysteresis and providing further evidence of the importance of ionic migration in modifying the efficiency of CH3NH3PbI3 devices.

Giant improper ferroelectricity in the ferroaxial magnet CaMn7O12.

In rhombohedral

Monoclinic crystal structure of α-RuCl3 and the zigzag antiferromagnetic ground state

{\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}

Realization of a three-dimensional spin–anisotropic harmonic honeycomb iridate

, an improper ferroelectric polarization of magnitude

New constraints on electron-beam induced halogen migration in apatite.

2870\text{ }\text{ }\ensuremath{\mu}\mathrm{C}\text{ }{\mathrm{m}}^{\ensuremath{-}2}

X-Ray Imaging and Multiferroic Coupling of Cycloidal Magnetic Domains in Ferroelectric Monodomain BiFeO 3

is induced by an incommensurate helical magnetic structure that evolves below

Noncoplanar and counterrotating incommensurate magnetic order stabilized by Kitaev interactions in γ-Li(2)IrO(3).

{T}_{\mathrm{N}1}=90\text{ }\text{ }\mathrm{K}

Incommensurate counterrotating magnetic order stabilized by Kitaev interactions in the layered honeycombα−Li2IrO3

. The electric polarization was found to be constrained to the high symmetry threefold rotation axis of the crystal structure, perpendicular to the in-plane rotation of the magnetic moments. The multiferroicity is explained by the ferroaxial coupling mechanism, which in

Electric field control of chiral magnetic domains in the high-temperature multiferroic CuO

{\mathrm{CaMn}}_{7}{\mathrm{O}}_{12}

Cu3Nb2O8: A Multiferroic with Chiral Coupling to the Crystal Structure

gives rise to the largest magnetically induced, electric polarization measured to date.