Optical properties and magnetochromism in multiferroic<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>BiFeO</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>

Abstract

In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of ${\text{BiFeO}}_{3}$. Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with ${\text{Fe}}^{3+}$ excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-field-temperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain reorientation near 10 T.