Nonlinear optical spectroscopy of magnetoelectric and piezomagnetic crystals

Abstract

We discuss new types of nonlinear time-noninvariant optical susceptibilities. that arise in crystals due to magnetic ordering. We show that different contributions to the nonlinear optical susceptibilities may coexist in magnetic materials that lead to a number of unusual optical effects. Experimental data are given for magnetoelectric antiferromagnet Cr²O³, piezomagnetic α-Fe₂O₃ and ferroelectric antiferromagnet YMnO₃. We developed a novel method to study antiferromagnetic domains by use of nonlinear spectroscopy. With use of the novel technique we confirm that in Cr₂O₃ in the spin-flop phase the antiferromagnetic vector is oriented along the twofold axis. In YMnO₃ we observed an unusual behaviour of antiferromagnetic domains which we explain by the entropy contribution to the domain wall energy.

Key Words:

• Cr₂O₃
• α-Fe₂O₃
• YMnO₃
• nonlinear susceptibilities
• antiferromagnetic domains