Pyroelectricity and field-induced spin-flop in (4-(Aminomethyl)pyridinium)2 MnCl4 · 2H2O

Large single crystals of (4-(Aminomethyl)pyridinium)2 MnCl4 · 2H2O (1) were grown by slow evaporation of solution. The crystal structure was solved to be Pī, which belongs to the central symmetric space group. But small pyroelectric current was detected, as well as a ferroelectric hysteresis loop. The pyroelectric and the ferroelectric properties were attributed to the strain caused by defects. Temperature-dependent magnetic curves and the M–H curve show that 1 is antiferromagnetic ordering below 2.5 K. A field-induced spin-flop is observed in the antiferromagnetic ordering state.


30-Mar-2020
Dear Dr Gao: Title: Pyroelectricity and field induced spin-flop in (4-(Aminomethyl)pyridinium)2MnCl4•2H2O Manuscript ID: RSOS-200271 Thank you for your submission to Royal Society Open Science. The chemistry content of Royal Society Open Science is published in collaboration with the Royal Society of Chemistry.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch. ********************************************** RSC Associate Editor: Comments to the Author: (There are no comments.) RSC Subject Editor: Comments to the Author: (There are no comments.) ********************************************** Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) In this work, the authors reported an Mn-based hybrid compound (4-(Aminomethyl)pyridinium)2MnCl4·2H2O with a P-1 space group, showing small pyroelectric current, as well as a ferroelectric hysteresis loop. The authors claimed that the pyroelectric and the ferroelectric property was attributed to the strain caused by defects. Moreover, temperaturedependent magnetic curves and the M-H curve shows an antiferromagnetic ordering behavior below 2.5 K and A field-induced spin-flop is observed in the antiferromagnetic ordering state. I believe the article passes the basic requirements for publication. There are, however, a number of changes that should be made to the article before publication to address a number of issues with the current version of the manuscript. 1. The introduction part needs to be reorganized, and the current version is poorly written. 2. The authors found that the title compound crystallizes in a centrosymmetric space group, but with pyroelectric and ferroelectric properties. The authors, however, infer only through guesswork that it is due to a stress defect in the crystal. This is not necessarily rigorous, and I strongly suggest that the author prove his conclusion by means of experiments. 3. PXRD pattern should be retested and the baseline should be recalibrated.

Reviewer: 2
Comments to the Author(s) 1. The section of Materials and Methods is over simplified. Please include more details of how the experiment isconducted. Schematic illustration might be helpful. 2. XRD results should be included in the main content as an inset picture of the Figure 1. 3. The author mentioned 'The ferroelectric and pyroelectric behavior in centrosymmetric compound 1 is similar to that in SrTiO3.'. Is there any figure of merit in terms of pyroelectricity to compare the performance of the two materials? 4. In the experimental section, the author indicated that 'a 1047 nm pulsed laser with a power of 100 mW' was used. Is it possible to choose other laser settings? 5. In figure 5, the author provided data of 2K, 5K, 50K and 300K. However, it is still not sufficient to see the trend given that only four temperatures are chosen. So, it should be more direct to catch the trend for readers if there are more measurements for other temperatures.

Comments to the Author(s)
The current version is suitable for publication.

Comments to the Author(s)
The authors have addressed my comments.
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Dear Editors and Reviewers:
Thank you for your letter and for the reviewers' comments concerning our manuscript entitled "Pyroelectricity and field induced spin-flop in (4-(Aminomethyl)pyridinium)2MnCl4•2H2O" (ID: RSOS-200271). Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied the comments carefully and have made corrections which we hope meet with approval. Revised portions are marked in red in the paper. The main corrections in the paper and the responds to the reviewer's comments are as following: Reviewer: 1 Comment 1: The introduction part needs to be reorganized, and the current version is poorly written. Response: The introduction part has been reorganized as:" Organic-inorganic hybrid perovskites have attracted great attention due to their rich and excellent physical properties(1-5). In hybrid perovskites crystals, BX6 octahedra play an important role in their multifunction property. Many ferroelectric materials have been found among organic-inorganic hybrid perovskite materials (4,(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). The octahedral structure is important for the ferroelectricity of hybrid perovskites. Some of the organic-inorganic hybrid perovskites are found to possess large spontaneous polarization and large piezoelectric coefficient that is comparable to those of inorganic materials. The excellent ferroelectric property and piezoelectric property of organic-inorganic perovskites make molecular based ferroelectrics become attractive in the field of application(20-22).
Here we report a compound (4-(Aminomethyl)pyridinium)2MnCl4·2H2O which have organic-inorganic hybrid perovskite structure. Pyroelectricity and field induced spin-flop was found in the single crystal of compound 1.
Flexoelectricity reflects a coupling between polarization and strain(23-26). Most materials have flexoelectric effect, in which a strain gradient could induce a polarization and a piezoelectric composite containing no piezoelectric elements. In centrosymmetric materials, a strain gradient can break the inversion symmetry. The strain induced polarization in SrTiO3 is widely studied. The crystal structure of SrTiO3 belong to the simple cubic centrosymmetric lattices and the dielectric permittivities of SrTiO3 is large. The ABX3 crystal structure and the large dielectric permittivities make it easy for strain to induce a polarization in the SrTiO3 single crystal(27, 28). Bulk photovoltaic bulk effect can also exist in SrTiO3, which is caused by flexoelectricity 4 . Pyroelectricity in 1 is similar that found in SrTiO3(29), which is not caused by the ferroelectricity or spontaneous polarization. The space group of singe crystal of 1 is Pī, which is centrosymmetric symmetry. However, small pyroelectric current is detected in 1 using Chnowth technology. Flexoelectric effect may play an important role in the pyroelectric effect in 1."