Monte Carlo simulation of pressure-induced phase transitions in spin-crossover materials

Pressure-induced phase transitions of spin-crossover materials were simulated by a Monte Carlo simulation in the constant pressure ensemble for the first time. Here, as the origin of the cooperative interaction, we adopt elastic interaction among the distortions of the lattice due to the difference of the molecular sizes in different spin states, i.e., the high spin (HS) state and the low spin (LS) state. We studied how the temperature dependence of the ordering process changes with the pressure, and we obtained a standard sequence of temperature dependences that has been found in changing other parameters such as strength of the ligand field (S. Miyashita et al., Prog. Theor. Phys. \textbf{114}, 719 (2005)). Various effects of pressure on the spin-crossover ordering process are examined from a unified point of view.Comment: 5 pages, 6 figure

Pembelajaran Lingkungan Bagi Siswa Rumah Baca Onomi Niphi, Kampung Yoboy, Kabupaten Jayapura, Papua

Abstract   Lake Sentani is located in Jayapura, Papua. Sentani people live in 26 villages along the coast and small islands around the lake. One of those islands is Yoboy Village, where a Onomi Niphi Reading House has been operating to provide library for elementary and senior high schools. The reading house is becoming center for various programs from various parties. Lake Sentani education program for students in Onomi Niphi Reading House was conducted to increase their knowledge of characteristics and fish species of Lake Sentani, as well as to develop digital education package and distributed to students in Yoboi Village and other students through social media. The program was conducted in Onomi Niphi Reading House, Jayapura at June 26 and July 3, 2021 through seminar and answer-question methods. Pretest was conducted before the class started and posttest applied after the class. Evaluation of the program was based on tests result and categorized to be distinguished, excellent, moderate, and poor. The test results showed the improvement of students’ knowledge on Lake Sentani. The documentation of the lake knowledge in digital format was distributed to the students and through social media. This will help the students to be aware of the improtance of conserving Lake Sentani.   Abstrak   Danau Sentani terletak di Kabupaten Jayapura, Papua. Danau ini ditempati oleh penduduk asli Sentani di 26 kampung yang menyebar di pulau-pulau dan tepian danau. Salah satunya adalah Kampung adat Yoboy, dimana terdapat Rumah Baca Onomi Niphi yang menyediakan perpustakaan bagi pelajar. Pembelajaran lingkungan tentang Danau Sentani diberikan kepada siswa Rumah Baca Onomi Niphi di kampung ini untuk meningkatkan pengetahuan mereka tentang karakteristik dan jenis-jenis ikan Danau Sentani, membuat media pembelajaran digital (video) nya serta menyebar luaskannya ke pelajar di rumah baca ini dan melalui berbagai media sosial. Pengabdian ini dilaksanakan di Rumah Baca Onomi-Niphi, Kampung Adat Yoboy, Kabupaten Jayapura, tanggal 26 Juni dan 3 Juli 2021 dalam bentuk ceramah dan tanya jawab. Pre test diberikan sebelum pembelajaran dan post test diberikan setelah pembelajaran. Evaluasi hasil pembelajaran ditentukan berdasarkan hasil-hasil test yang dikelompokkan menjadi kategori sangat baik, baik, cukup dan kurang. Hasil pre test dan post test pada pembelajaran tentang Danau Sentani menunjukkan bahwa pengetahuan anak-anak meningkat setelah pembelajaran lingkungan tentang Danau Sentani. Dokumentasi materi pembelajaran dalam bentuk digital dan penyebar luasannya diharapkan dapat mempertahankan pengetahuan anak tentang Danau Sentani.  Pengetahuan ini diharapkan dapat meningkatkan kepedulian anak terhadap Danau Sentani. &nbsp

Poly[[hexa-μ-cyanido-manganese(II)iron(III)] penta­hydrate]

The structure of the title compound, MnII[FeIII(CN)6]2/3·5H2O, features a face-centered cubic –Mn—NC—Fe– framework with both Mn and Fe having site symmetry m m. Since one-third of the [Fe(CN)6]3− units are missing for a given formula in order to maintain charge neutrality, each Mn atom around such a vacancy is coordinated not only by the N atoms of the CN groups but also by the O atoms of the ligand water mol­ecules. In addition to ligand water mol­ecules, two types of non-coordinated water mol­ecules, so-called zeolitic water mol­ecules, exist in the inter­stitial sites of the –Mn—NC—Fe– framework. The positions of the O atoms of the zeolitic water mol­ecules are fixed by the linkage via hydrogen bonds between ligand water and zeolitic water mol­ecules. The structure is related to a recently reported rubidium manganese hexa­cyano­ferrate. Site occupancy factors for Fe, C, N are 0.67; for two O atoms the value is 0.83 and for one O atom is 0.17

Structure of Metastable States in Phase Transitions with High-Spin Low-Spin Degree of Freedom

Difference of degeneracy of the low-spin (LS) and high-spin (HS) states causes interesting entropy effects on spin-crossover phase transitions and charge transfer phase transitions in materials composed of the spin-crossover atoms. Mechanisms of the spin-crossover (SC) phase transitions have been studied by using Wajnflasz model, where the degeneracy of the spin states (HS or LS) is taken into account and cooperative natures of the spin-crossover phase transitions have been well described. Recently, a charge transfer (CT) phase transition due to electron hopping between LS and HS sites has been studied by using a generalized Wajnflasz model. In the both systems of SC and CT, the systems have a high temperature structure (HT) and a low temperature structure (LT), and the change between them can be a smooth crossover or a discontinuous first order phase transition depending on the parameters of the systems. Although apparently the standard SC system and the CT system are very different, it is shown that both models are equivalent under a certain transformation of variables. In both systems, the structure of metastable state at low temperatures is a matter of interest. We study temperature dependence of fraction of HT systematically in a unified model, and find several structures of equilibrium and metastable states of the model as functions of system parameters. In particular, we find a reentrant type metastable branch of HT in a low temperature region, which would play an important role to study the photo-irradiated processes of related materials.Comment: 19 pages, 11 figure

Bulk and surface switching in Mn-Fe-based Prussian Blue Analogues

Many Prussian Blue Analogues are known to show a thermally induced phase transition close to room temperature and a reversible, photo-induced phase transition at low temperatures. This work reports on magnetic measurements, X-ray photoemission and Raman spectroscopy on a particular class of these molecular heterobimetallic systems, specifically on Rb0.81Mn[Fe(CN)6]0.95_1.24H2O, Rb0.97Mn[Fe(CN)6]0.98_1.03H2O and Rb0.70Cu0.22Mn0.78[Fe(CN)6]0.86_2.05H2O, to investigate these transition phenomena both in the bulk of the material and at the sample surface. Results indicate a high degree of charge transfer in the bulk, while a substantially reduced conversion is found at the sample surface, even in case of a near perfect (Rb:Mn:Fe=1:1:1) stoichiometry. Thus, the intrinsic incompleteness of the charge transfer transition in these materials is found to be primarily due to surface reconstruction. Substitution of a large fraction of charge transfer active Mn ions by charge transfer inactive Cu ions leads to a proportional conversion reduction with respect to the maximum conversion that is still stoichiometrically possible and shows the charge transfer capability of metal centers to be quite robust upon inclusion of a neighboring impurity. Additionally, a 532 nm photo-induced metastable state, reminiscent of the high temperature Fe(III)Mn(II) ground state, is found at temperatures 50-100 K. The efficiency of photo-excitation to the metastable state is found to be maximized around 90 K. The photo-induced state is observed to relax to the low temperature Fe(II)Mn(III) ground state at a temperature of approximately 123 K.Comment: 12 pages, 8 figure

Photoinduced Magnetization in a Thin Fe-CN-Co Film

The magnetization of a thin Fe-Co cyanide film has been investigated from 5 K to 300 K and in fields up to 500 G. Upon illumination with visible light, the magnetization of the film rapidly increases. The original cluster glass behavior is further developed in the photoinduced state and shows substantial changes in critical temperature and freezing temperature.Comment: 2 pages, 2 figures, 1 table, International Conference on Magnetism 200