Anisotropy study of multiferroicity in the pyroxene NaFeGe2O6

Abstract

We present a study of the anisotropy of the dielectric, magnetic and magnetoelastic properties of the multiferroic clinopyroxene NaFeGe _2 O _6 . Pyroelectric currents, dielectric constants and magnetic susceptibilities as well as the thermal expansion and the magnetostriction were examined on large synthetic single crystals of NaFeGe _2 O _6 . The spontaneous electric polarization detected below ${{T}_{{\rm C}}}\simeq 11.6\;{\rm K}$ in an antiferromagnetically ordered state ( ${{T}_{{\rm N}}}\simeq 13\;{\rm K}$ ) is mainly lying within the ac plane with a small component along ${\boldsymbol{b}} $ , indicating a triclinic symmetry of the multiferroic phase of NaFeGe _2 O _6 . The electric polarization can be strongly modified by applying magnetic fields along different directions. We derive detailed magnetic field versus temperature phase diagrams and identify three multiferroic low-temperature phases, which are separated by a non-ferroelectric, antiferromagnetically ordered state from the paramagnetic high-temperature phase.

Keywords

• multiferroic
• pyroxene
• magnetoelectric
• 75.85.+t
• 77.80.-e
• 75.30.Cr