Magnetic interactions in pristine and magnetically doped halide-perovskites

Efrat Lifshitz, Alyssa Kostadinov and Arthur Shapiro, Technion – Israel Institute of Technology, Haifa, Israel; Maryna Bodnarchuk, Maksym Kovalenko, ETH, Zurich, Switzerland; Liang Tan, Andrew Rappe, Pennsylvania University, Philadelphia, USA. (ssefrat@technion.ac.il)

organic-inorganic perovskites have become one of the most promising materials in various opto-electronic applications. The best performance was found in compounds with general chemical formula, ABX3, when A is either organic or inorganic cation, like methylammonium (MA+), formamidinium (FA+) or Cs+, B is a bivalent metal cation, such as Pb2+or Sn+2 and X is a halide, Cl−, Br−, or I−. Those compounds can be further modified by a post treatment which exchange small percent of the halide anions, as well as a few metal cations with magnetic dopants. Mixed composition renders new properties beyond those of the pristine compounds.

present work describes magnetic properties in pristine and magnetically doped Cs (MA) PbBr3 perovskites produced as nanocubes or as bulk crystals. pristine perovskites were synthesized at the ETH laboratory, while the mixed halide compounds or/and magnetically doped derivatives were recently prepared at the Technion. study focused on the investigation of magneto-optical properties of the discussed compounds, via examination of polarized magneto-photoluminescence or optically detected magnetic resonance spectroscopy. The pristine perovskites exhibit linear and circular polarized emission at any magnetic field up to 8 Tesla, with a field dependence that deviates from a Zeeman-effect. A theoretical work (carried out by the Rappe group) corroborated the occurrence of a Rashba-effect stimulated by the dynamic liability of the counter ions, Cs or MA and the consequence breaking of inversion of symmetry. Furthermore, the observations indicated the occurrence of an additional magnetic phenomenon, related to nuclear spin polarization induced by the formation of an exciton (the so-called Overhouser effect), and mainly associated with intrinsic neutral abundance of the Pb metal isotope.

The magnetically doped derivatives of halide perovskites included partial dual exchange of halide and metal cations: Br was exchanged with Cl and Pb was exchanged in a limited fashion with isovalent Ni cations, the last including unpaired spins. The magnetic resonance measurement designated the integration of Ni at substitutional position with a characteristic hyperfine interactions. Thus, magnetic dopants produce additional internal magnetic coupling between photo-generated specie and guest electron and nuclear spins.