Magnetic field-temperature phase diagram of multiferroic [(CH3)2NH2]Mn(HCOO)3<

Abstract

We combined pulsed field magnetization and first principles spin density calculations to reveal the magnetic field-temperature phase diagram and spin state character in multiferroic [(CH3)2NH2]Mn(HCOO)3. Despite similarities with the rare earth manganites, the phase diagram is analogous to other Mn-based quantum magnets with a 0.31 T spin flop, a 15.3 T transition to the fully polarized state, and short range correlations that persist above the ordering temperature. The experimentally accessible saturation field opens the door to exploration of the high field phase.

Phonon mode links ferroicities in multiferroic [(CH3)2NH2]Mn(HCOO)3Hughey1, Clune2, Yokosuk3 et al. 2017Phys. Rev. B18030View full textAdd to dashboardCite

“…Curiously, cross-coupling between the electric and magnetic orders [8,15,16] extends to relatively high temperatures [8,9], demonstrating that a low ordering temperature may not be a barrier to strong magnetoelectric coupling -although the precise mechanism for this effect has not yet been resolved. Magnetic field drives the system through a spin-flop transition at 0.31 T and into the fully saturated magnetic state at 15.3 T [17]. These energy scales are summarized in Fig.…”

“…1(b). In addition to representing a class of relatively unexplored multiferroics with flexible molecular architectures, the experimentally accessible transition temperatures and critical fields in [(CH 3 ) 2 NH 2 ]Mn(HCOO) 3 [6,17] are ideal for exploring the interplay between charge, structure, and magnetism. In this Letter, we unveil an unusual signature of this interaction: a phonon that is sensitive to the development…”

“…Ferroelectricity develops across the order-disorder transition [6,7]. The formate bridges define the Mn-O-C-O-Mn superexchange pathway (J = -0.69 K) [17,18]. (b) Summary of important temperature and magnetic energy scales [6,10,17].…”

“…The formate bridges define the Mn-O-C-O-Mn superexchange pathway (J = -0.69 K) [17,18]. (b) Summary of important temperature and magnetic energy scales [6,10,17]. PM = paramagnetic, cAFM = canted antiferromagnet, PE = paraelectric, FE = ferroelectric, BSF = spin-flop field, and BC = saturation field.…”

“…In order to explore what might control these ferroicities and the mechanisms that underlie the field dependent properties above T N [8,9], we measured the in-frared vibrational response of [(CH 3 ) 2 NH 2 ]Mn(HCOO) 3 and compared our findings with complementary lattice dynamics calculations and prior magnetization measurements [17]. We find that doublet splitting of the formate bending mode across T C functions as a ferroelectric order parameter and that the same phonon mode is sensitive to the development of the fully saturated magnetic state above 15.3 T. A single fundamental excitation in the form of a phonon thus underpins the development of the ferroic phases and magnetoelectric coupling -even though T C and T N are quite different.…”