New Constraints On Electron-Beam Induced Halogen Migration In Apatite

American Mineralogist Mineralogical Society of America 100:1 (2015) 281-293

Authors:

Michael J Stock, Madeleine CS Humphreys, Victoria C Smith, Roger D Johnson, David M Pyle, Eimf

Unconventional magnetic order on the hyperhoneycomb Kitaev lattice in β-Li2IrO3: Full solution via magnetic resonant x-ray diffraction

Physical Review B American Physical Society (APS) 90:20 (2014) 205116

Authors:

A Biffin, RD Johnson, Sungkyun Choi, F Freund, S Manni, A Bombardi, P Manuel, P Gegenwart, R Coldea

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

Physical review letters 113:19 (2014) 197201

Authors:

A Biffin, RD Johnson, I Kimchi, R Morris, A Bombardi, JG Analytis, A Vishwanath, R Coldea

Abstract:

Materials that realize Kitaev spin models with bond-dependent anisotropic interactions have long been searched for, as the resulting frustration effects are predicted to stabilize novel forms of magnetic order or quantum spin liquids. Here, we explore the magnetism of γ-Li(2)IrO(3), which has the topology of a three-dimensional Kitaev lattice of interconnected Ir honeycombs. Using magnetic resonant x-ray diffraction, we find a complex, yet highly symmetric incommensurate magnetic structure with noncoplanar and counterrotating Ir moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally accounts for all key features of the observed magnetic structure. Our results provide strong evidence that γ-Li(2)IrO(3) realizes a spin Hamiltonian with dominant Kitaev interactions.

The roles of chirality and polarity in novel multiferroics: MnSb 2 O 6 and Cu 3 Nb 2 O 8

Acta Crystallographica Section A: Foundations and advances International Union of Crystallography (IUCr) 70:a1 (2014) c386-c386

Authors:

Roger Johnson, Laurent Chapon, Kun Cao, Pascal Manuel, Alessandro Bombardi, Sunil Nair, Sang-Wook Cheong, Paolo Radaelli

CaBaCo4O7: A ferrimagnetic pyroelectric

Physical Review B American Physical Society (APS) 90:4 (2014) 045129

Authors:

RD Johnson, K Cao, F Giustino, PG Radaelli