Developing the Pressure–Temperature–Magnetic Field Phase Diagram of Multiferroic [(CH₃)₂NH₂]Mn(HCOO)₃

Abstract

We combined Raman scattering and magnetic susceptibility to explore the properties of [(CH 3 ) 2 NH 2 ]Mn-(HCOO) 3 under compression. Analysis of the formate bending mode reveals a broad two-phase region surrounding the 4.2 GPa critical pressure that becomes increasingly sluggish below the order−disorder transition due to the extensive hydrogen-bonding network. Although the paraelectric and ferroelectric phases have different space groups at ambient-pressure conditions, they both drive toward P1 symmetry under compression. This is a direct consequence of how the order−disorder transition changes under pressure. We bring these findings together with prior magnetization work to create a pressure−temperature−magnetic field phase diagram, unveiling entanglement, competition, and a progression of symmetry-breaking effects that underlie functionality in this molecule-based multiferroic. That the high-pressure P1 phase is a subgroup of the ferroelectric Cc suggests the possibility of enhanced electric polarization as well as opportunity for strain control.

Metal-Formate Framework Stiffening and Its Relevance to Phase Transition Mechanism

“…MOFs have received a great deal of attention due to their potential applications as catalysts, biomedical sensors, and luminescent materials [ 1 , 2 , 3 , 4 , 5 ]. Most efforts have been devoted to dimethylammonium MOFs with the general formula ((CH 3 ) 2 NH 2 )(M(HCOO) 3 ) (DMAM, where M denotes divalent metal ions) [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. These compounds consist of metal centers M 2+ related by HCOO − anionic ligands within the frameworks with pseudo-cubic nanocavities [ 15 , 21 ].…”

Metal Site Substitution and Role of the Dimer on Symmetry Breaking in FePS3 and CrPS4 under Pressure

“…Obviously, infrared and Raman scattering spectroscopies are complementary techniques. Both are needed for a full symmetry analysis of phonons in this material. , Infrared also reveals electronic properties like metallicity. Typical signatures include the development of a Drude and screening of phonons.…”

Pressure-induced shift of effective Ce valence, Fermi energy and phase boundaries in CeOs$_4$Sb$_{12}$

“…It can allow the investigation of quantum criticality [23,24,25], manipulate the band structure [26,27] and lead to the emergence of new (superconducting) phases [28,29] that would not be accessible at ambient pressure. In contrast to alloying, the application of pressure not only preserves sample symmetry [30,31,32] and introduces little disorder, but it is also continuous and reversible. In this paper we present results on the pressure dependence of the phase boundaries of the high-temperature H-to-L transition, of the S-phase boundary and on the influence of pressure on the high-field Fermi surface and electronic band structure, and the corresponding effective masses.…”