Observation of magnetic excitons in

¹ Department of Physics, University of Durham - South Road, Durham, DH1 3LE, UK
² Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut CH-5332, Villigen, PSI, Switzerland
³ Department of Physics, University of Oxford - Oxford, OX1 3PU, UK
⁴ Department of Chemical Engineering and Materials Science, University of Minnesota 421 Washington Ave SE, Minneapolis 55455, USA

Received: 25 November 2004
Accepted: 14 April 2005

Abstract

An impurity-driven magnetic phase transition has been investigated in at temperatures below that of the thermally induced spin state transition of the ion. We have discovered a saturating component of the magnetisation, which we attribute to previously unobserved interactions between magnetic excitons. These conclusions are confirmed by muon spin spectroscopy which indicates an ordering temperature of 50 in both the transverse and zero-field configurations. Low-energy muon measurements demonstrate that the magnetic behaviour is independent of implantation energy and hence a property of the bulk of the material. The magnetic exciton formation is attributed to the interaction between electrons bound at oxygen vacancies and neighbouring cobalt ions, and is proposed as the precursor to the magneto-electronic phase separation recently observed in doped lanthanum cobaltite.