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.
An unusual high magnetic hardness for the layered perovskite-like (C2H5NH3)2[Fe(II)Cl4], in addition to its already found canted antiferromagnetism, ferroelasticity, and ferroelectricity, which are absent for (CH3NH3)2[Fe(II)Cl4], has been observed. The additional CH2 in the ethylammonium compared to methylammonium allows more degrees of freedom and therefore numerous phase transitions which have been characterized by single-crystal structure determinations from 383 to 10 K giving the sequence from tetragonal to orthorhombic to monoclinic (I4/mmm ↔ P42/ncm ↔ Pccn ↔ Pcab ↔ C2/c) accompanied by both tilting and rotation of the FeCl6 octahedra. The magnetic properties on single crystal and powder samples at high temperature are similar for both compounds, but at TN (C2H5NH3)2[Fe(II)Cl4] is a proper canted antiferromagnet unlike the hidden canting observed for (CH3NH3)2[Fe(II)Cl4]. The canting angle is 0.6° toward the c-axis, and thus the moments lie in the easy plane of the iron-chloride layer defined by a critical exponent β = 0.18. The isothermal magnetizations for the field along the three orthogonal crystallographic axes show wider hysteresis for H ∥ c and is present at all temperature below 98 K. The coercive field increases as the temperature is lowered, and at T < 20 K it is difficult to reverse all the moments with the available 50 kOe of the SQUID for both single crystal and powder samples. The shape of the virgin magnetization after zero-field-cool (ZFC) indicates that the high coercive field is due to domain wall pinning. Thus, there are unusual associated anomalies such as asymmetric hysteresis and history dependence. The difference in magnetic hardness of the two compounds suggests that magnetic, electric, and elastic domains are intricately manifested and therefore raise the key question of how the different domains interact.
C11H7Co 2 N 3 O7, triclinic, P¯ (no. 2), a = 7.8744(6) Å, b = 9.2561(9) Å, c = 9.6688(9) Å, α = 65.775(9)°, β = 87.625(7)°, γ = 73.654(8)°, V = 614.48(11) Å 3 , Z = 2, Rgt(F) = 0.0537, CCDC no.: 1506236A representative part of the coordination polymer forming the crystal structure is shown in the gure (′ = x, 1 + y, z). Tables 1 and 2 contain details of the measurement method and a list of the atoms including atomic coordinates and displacement parameters. Source of materialA mixture of CoCl 2 ·2H 2 O (0.1 mmol, 0.024 g), 1,2,4 triazole (Htrz) (13.9 mg, 0.2 mmol), and benzene-1,3,5-tricarboxylic acid (H 3 btc) (21.0 mg, 0.1 mmol) was dissolved in 5 mL DMF and 2 mL EtOH. The mixture was then transferred into a 20 mL vial and heated to 80°C, and hold for 60 h. Then the reactant mixture was cooled at a rate of 10°C/min to lead to the formation of crystals in 36% yield based on Co(II) ion. Experimental detailsThe H atoms bonded to C were positioned geometrically and re ned using a riding model, with C-H = 0.93 Å with U iso (H) = 1.2 times Ueq(C). DiscussionThere is a general interest in 1,2,4-triazoles [1]. Structural analysis suggests that there are three crystallographically independent Co(II) ions, one deprotonated trz − ligand and one deprotonated btc 3− ligand in the asymmetric unit. Co1 (occupancy 1/2) is six-coordinated by four carboxylic O atoms from four di erent btc 3− ligands and two N atoms from two di erent trz − ligands, forming a octahedral coordination; Co2 is ve-connected with four carboxylic O atoms from four di erent btc 3− ligands and one N atom from one trz − ligand; Co3 (occupancy 1/2) is six-coordinated again
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