Critical phenomena of multiferroics under high magnetic fields

Kee Hoon Kim, Seoul National University

The multiferroics wherein at least two ferroic orders such as ferroelectricity and magnetism are cross-coupled provide unprecedented opportunities to study magnetic properties of frustrated spin system through investigation of dielectric properties. In this presentation, I’ll introduce two unique multiferroic compounds BiMn₂O₅ and Ba₂CoGe₂O₇, both of which has electric polarization induced by antiferromagnetic spin ordering. In the former, we have recently found a magnetic field induced critical end point at very low temperatures due to the unique feature of the spin-flop transition [1]. In the latter, we have observed that combination of noncentrosymmetric structure and Dzyaloshinskii-Moriya interaction within antiferromagnetic spin structure can generate a pyroelectric polarization below 7 K. When high magnetic field around 39 T is applied, the canted antiferromagnetic spin structure shows a second order phase transition into the collinear spin state. Around this quantum critical point, we have observed clear features of quantum critical fluctuation through dielectric properties, which renders us uncover the universality of this transition as well as characteristic phase boundaries near quantum critical point. This finding in turn points out a new avenue of researches in the physics of quantum criticality. 

References

[1] J. W. Kim et al., Proc. Nat’l Acad. of Sci. 106, 11573 (2009)

[2] J. W. Kim et al. to be submitted.

In close collaboration with J. W. Kim, S-.W. Cheong, Jung-Hoon Han, Gun-Sang Jeon, C. D. Batista.