Domain switching and exchange bias control by electric field in the multiferroic conical magnet Mn2GeO4

Abstract

We present a study of the dielectric, structural, and magnetic properties of the multiferroic or linear magnetoelectric substitution series [(NH 4) 1−x K x ] 2 [FeCl 5 (H 2 O)]. Pyroelectric currents, magnetic susceptibilities, and thermodynamic properties were examined on large single crystals of the erythrosiderite compounds and detailed magnetic-field versus temperature phase diagrams are derived for three different substitution levels. With increasing potassium concentration the material is tuned from a multiferroic (x 0.06) to a linear magnetoelectric (x 0.15) ground state. In contrast to the respective pure parent compounds with x = 0 or 1, however, the ferroelectric or linear magnetoelectric polarization in none of the substituted samples is switchable by external electric fields because these samples exhibit a significant electric polarization already above the magnetic ordering transition. The polarization arises at a higher-lying structural phase transition that is examined by THz spectroscopy, and, on a deuterated pure single crystal, by comprehensive neutron-diffraction experiments. The structural phase transition is attributed to an ordering of NH + 4 tetrahedra but does not break inversion symmetry in the pure material, while a finite K content causes pyroelectricity.

Evolution of magnetic order in multiferroic Pb(Fe2/3W1/3)O3‐BiFeO3 solid solution

“…Secondly, in multiferroics the cross‐couplings between strain, electric order and magnetic order and their conjunctive fields are commonly observed 35‐37 . In the present case, the coupled heterovalent substitutions of Bi 3+ for Pb 2+ on the A‐site and Fe 3+ for (Fe 2/3 W 1/3 ) 4+ on the B‐site and the resultant increased microscopic compositional disorder and charge/strain fluctuations may also influence the superexchange couplings by acting as an additional perturbation.…”

Axion-matter coupling in multiferroics

“…However, ferromagnetic order in these materials, which is much soughtafter, is rare. Established ferromagnetic cases include CoCr 2 O 4 68 , DyFeO 3 69 , GdFeO 3 70 , Mn 2 GeO 4 [71][72][73][74] , and more recently hexagonally grown Lu 1−x Sc x FeO 3 (h-LSFO) with x ≈ 0.4 32,33 . Among these, the subset with P M is practically limited to the latter four, though the polarizations are not spontaneous in DyFeO 3 .…”

“…As a second promising material platform we mention the olivine compound Mn 2 GeO 4 71,74 . In this material the ferroic orders originate from spiral spin-order, resulting from transverse conical chains that yield a net magnetization and electric polarization pointing along the c direction.…”