On the Nature of the Structural and Magnetic Phase Transitions in the Layered Perovskite-Like (CH₃NH₃)₂[Fe^IICl₄]

Abstract

In view of renewed interest in multiferroic for molecular systems, we re-examine the structural and magnetic properties of the potentially ferroic layered perovskite-like (CH3NH3)2[Fe(II)Cl4] due to its high-temperature magnetic ordering transition. The structures from several sets of diffraction data of single crystals consist of square-grid layers of corner-sharing FeCl6 octahedra and changes from the high-symmetry I4/mmm (T > 335 K) to the low-symmetry Pccn (T < 335 K). In the former the iron and bridging chlorine atoms are within the layer and the organic cations sit in the middle of each square grid, while in the latter the octahedra are tilted in pairs, two in and two out, progressively by up to 12° and the nitrogen atoms follow their motion to be nearer to the two-in pairs. Crystals are stable up to 450 K and display three phase transitions, two structural at 332 and 233 K and one magnetic at 95 K. The temperature dependences of the dc magnetization (zero-field and field-cooling modes) in different applied fields (10-10,000 Oe) on several aligned single crystals independently reveal a hidden-canted antiferromagnetic ground state of at least four sublattices and not the reported canted antiferromagnetic ground state. A metamagnetic critical field of only 200 Oe transforms it to a canted antiferromagnet. The estimated canting angle is 1.4° in zero field, and it folds to ca. 2.8° in a field of 50 kOe at 2 K. The easy axis is along 010, the hard axis is along 100, and the intermediate and canting axis is 001. Using the available extracted parameters the phase diagram has been constructed. This study provides evidence of a complex and intricate manifestation of the orientation, temperature, and field dependence of the interplay between anisotropy and coherent lengths, which would need further studies.

Progress on lead-free metal halide perovskites for photovoltaic applications: a review

“…The layered perovskites are made up of alternating stacks of organic (alkyl, aryl) ammonium and inorganic metal–halogen sheets of corner-sharing FeX 6 octahedra [144]. Even though various hybrid iron halide perovskites such as (RNH 3 ) 2 FeCl 4 (R = CH 3 , C 2 H 5 , C 3 H 7 , C 6 H 5 CH 2 ), (CH 3 NH 3 ) 2 FeCl 2 Br 2 , (CH 3 NH 3 ) 2 FeCl 4 , and (CH 3 NH 3 ) 2 FeCl 3 Br have been investigated with regard to their magnetic properties, only a few studies pay attention to the electrical and optical properties [129, 143–145].…”

Potential Substitutes for Replacement of Lead in Perovskite Solar Cells: A Review

“…The divalent Fe 2+ has a smaller ionic radius (78 pm) as compared to Pb 2+ (119 pm) that does not allow the formation of 3D perovskite structure. Iron‐based 2D layered perovskite (CH 3 NH 3 ) 2 (FeCl 4 ) exhibits a canted anti‐ferromagnetism in a magnetic field of strength greater than 2000 Oe and it also exhibits the phase transition from a high symmetry to a low symmetry . The magnetic susceptibility of (CH 3 NH 3 ) 2 FeCl 3 Br perovskite depends upon the strength of applied magnetic field.…”

“…Iron-based 2D layered perovskite (CH 3 NH 3 ) 2 (FeCl 4 ) exhibits a canted anti-ferromagnetism in a magnetic field of strength greater than 2000 Oe and it also exhibits the phase transition from a high symmetry to a low symmetry. [287] The magnetic susceptibility of (CH 3 NH 3 ) 2 FeCl 3 Br perovskite depends upon the strength of applied magnetic field. Also, the size of halide anion has a direct effect on the canted spin.…”

Progress and Perspective in Low‐Dimensional Metal Halide Perovskites for Optoelectronic Applications

“…Furthermore, with different organic cations, a series of copper‐based layered perovskites with various large organic cations including (CH 3 CH 2 CH 2 CH 2 NH 3 ) 2 CuBr 4 , (C 5 H 9 NH 3 ) 2 CuBr 4 , (C 6 H 5 CH 2 CH 2 NH 3 ) 2 CuCl 4 , (C 8 NH 6 CH 2 CH 2 NH 3 ) 2 CuCl 4 are explored with ferromagnetic and photovoltaic applications (Figure d) . In addition, ferrous perovskite (CH 3 NH 3 ) 2 Fe(II)Cl 4 and germanium‐containing perovskite (C 6 H 5 C 2 H 4 NH 3 ) 2 GeI 4 (Figure e) also tend to form layered structures, due to the similarity in their ionic radii of metal cations …”