Magnets are composed of single atoms or ions, and the three-dimensional magnetic order mainly comes from the magnetic interaction transmitted through chemical bonds, and its preparation adopts metallurgical or other physical methods. Molecular magnet is a new kind of soft material which is composed of molecules or ions. Molecular-based materials (materials with three-dimensional magnetic order below the temperature of molecular 2 base mainly come from intermolecular interaction) have become chemists and materials, and their preparation adopts conventional organic or inorganic chemical synthesis methods. Because psychologists and biologists attach great importance to the emerging scientific fields, it has been reported that Tc can reach 340 K stably: molecular ferromagnet similar to Prussian blue. (1) orthogonality of magnetic orbits According to the molecular orbital theory of Kahn et al., the magnetic interaction (J) between paramagnetic ions A and B consists of two parts: the physical basis of molecular magnetism, namely ferromagnetic contribution and antiferromagnetic contribution, J = JF+ JAF. When the magnetic orbit occupied by unpaired electrons in A and the magnetic molecular magnet occupied by unpaired electrons in B come from the overlapping of unpaired electrons in molecules, their interactions are antiferromagnetic coupling, intermolecular coupling and these couplings. When the unpaired electricity in A and B comes from intermolecular, and the spin-spin interaction in the molecule is often orthogonal through the magnetic orbits occupied by protons, the interaction between them is ferromagnetic "chemical bridge" to realize magnetic super-interaction. Therefore, the molecular magnetic materials are also coupled, as shown in (a) and (b) in figure (1). If there is magnetic dipole-dipole interaction between ferromagnetic coupling and antiferromagnetic coupling, under normal circumstances, antiferromagnetic coupling is stronger than ferromagnetic coupling, so only magnetism shows more colorful magnetism than conventional inorganic magnetic materials. When JAF is zero, there is ferromagnetic coupling between a and b, for example, in csni Ⅱ Ⅱ. In recent years, Verdaguer, a French scientist, found that Prussian blue complexes showed higher transition temperature and greater coercivity. Prussian blue magnetic complexes have attracted more and more attention [25]. Prussian blue molecular magnet is a bimetallic complex based on building element M(CN)k-6 and simple metal ions bridged by cyano, and the bimetallic ions are all in octahedral coordination environment. They are connected into a three-dimensional network by cyanogen bridge. The composition form is MK [m' (CN) 6] L NH2O or AMK [m' (CN) 6] L NH2O (M and M' are different paramagnetism, and the compound is ferromagnetic. As shown in fig. 2, the triazole ligand is magnetically exchanged with metal ions and corresponding Cu3 [Cr (CN) 6] 2.15h2o (TC = 66k), Cu3 [Fe (CN) 6] 2. 12h4. Monomolecular magnet) 2O (TC = 65438. 2. 14h2o (TC = 23k) are all ferromagnetic. If the magnetic orbits of two metal ions overlap, the above-mentioned magnetic conditions between them are that molecules are connected to form polymers, resulting in very strong coupling, and the compounds are antiferromagnetic or ferrimagnetic, such as intermolecular interaction. On the other hand, if the intermolecular interaction (net4) is 0.5mn1.25 [v (cn) 6] 2h2o (TC = 230k), and Cr Ⅱ 3 [Cr Ⅲ] can be ignored, then the molecule is isolated as an independent magnetic molecule. When (cn) 6] 2.10h2o (TC =1994-2008 China Academic Journals Electronic Publishing House. All rights reserved. The magnetic moment of +0 in monograph No.65438 of ki.net Nature Miscellanies, Volume 24 is determined by the lowest energy state after magnetic coupling. At this point, the domain may appear. It is mentioned that the ground state of molecular-based iron whose transition temperature exceeds room temperature is a stable state with high spin number, and the discovery of quasi-magnetic and ferrimagnetic materials is produced under the action of magnetic field. The polynuclear complex with high spin is in the continuous excited state energy level, so the magnetic moment of the whole molecule shows the discovery of magnetic monomolecular magnet at low temperature under the action of external field. When deflecting in the field direction higher than room temperature, it is necessary to overcome a large potential barrier, which leads to the discovery of spin-crossing complexes with large hysteresis. The magnetic anisotropy of molecular-based magnets splitting from zero field is sometimes called magneto-optical and thermomagnetic effects of spin resistance; And GMR and CMR effects of molecular-based magnets [32]. This bistability (bist2, etc. ) depends on the external magnetic field, which indicates the bright future of molecular magnetic materials. This ability is regarded as the basis of the application of new generation information materials. Compared with traditional magnetic materials, the existing monomolecular magnets mainly include Mn 12 and Mn 65432, because of their wide chemical selectivity. Clusters with V as magnetic material and 4-ion clusters, such as Mn 12 whose ground state is S = 10, have the advantages of small volume, low relative density, low energy consumption (O[33], diversified structure and so on, and most of their preparation methods are conventional 2cme) 16 (H2O). It can be considered as a magnetized nano-chemical method with a single size, which is convenient for making various forms of products. It is a rice material with immeasurable application prospect. Some traditional magnetic materials are irreplaceable. It is found that this kind of new materials may become various high-tech materials, especially the new generation of information storage. 5. Spin-crossed composites. Of course, as we all know, as a new material, many aspects still need to be studied and improved gradually when the spin ion center in the complex molecule is reduced to, which is also a good opportunity for China scientists to be at the forefront of the world in basic research and application, and the interaction between molecules is very small, so the complex shows the characteristics of independent ions. It can be predicted that it will be nearly ideal paramagnetism in the future development. The molecular-based magnetic materials of transition metal complexes with 3d4- 3d7 electronic configuration will probably be: ① high, octahedral coordination structure. ② Coordination field E can affect the arrangement of five-dimensional electron orbitals and improve the physical stability of materials; ③ transparent insulated magnet; (4) The influence of energy gap δ between molecular magnetic orbitals that are easily changed and treated by G and t2g; ⑤ When the average electron pair energy of P-phase material is close to the composite magnetic material with other physical properties; ⑥ Ultra-hard and ultra-soft magnets; ⑦ liquid magnets and other aspects focus on exploration and come to the conclusion that the spin state of the compound may be developed due to the perturbation of some external conditions, which can be manifested as the cross transition between high spin state and low spin state [34]. Some Fe (II) complexes (most typically received on August 29th, 2000) have high spin states of 5t1Alivisatos A.P., Barbara P.F, Castleman a.w, et al. adv. ma22(s = 2, paramagnetic) and ters. , 1998; 10: 1297 low spin state 1A 1(S =0, diamagnetism), accompanied by spin phase transition, 2 McConnell H.M.J.Chem.Phys.,1963; 39: 19 10, the structure and even color of the compound may change. The transition temperature of some compounds is 3. Chemical research1967; 1 1: 144 is still in the normal temperature zone, such as [Fe (htrz) 4 Wickman H.H., Trozzolo A.M, Williams H.J, et al. Phys.Rev, 3-3x (NH2TRZ). 155:563(trz= 1, 2,4 triazole), rising from purple (low spin) at a temperature of 5miller j.s., Calabrese J.C, Epstein A.J, etc. American chemical society at room temperature. 10266 Pei Y, Verdauger m., Kahn O. et al. Chemistry. Socialists, 1986; State phenomenon [35]. 1984, Decurtins et al. first observed the cross effect of light-induced spin from 108:7428 [36], and then excited the spin state 7 by light at low temperature, Manrique ZJ.M, Yee G.T, McLean R.S, et al. 378:70 1 and memory [34]. China has also made gratifying achievements in the study of spin crossover. 9 Marat, Thiebaut S, Dagger M, et al. 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Wang Zhan, 16 Miller, Zhang Jihai, Rafe, etc., Journal of Physical Chemistry,1987; 9 1:4344 as a new material, in recent ten years17millerj.s., Calabressj.c, Dixon.a, et al.j.am.chem.soc.,1987; 109:769 With the efforts of chemists and physicists, 18 Zhou P., Longs.M, Millerj.S. Phys.Lett.A, 1993 has made achievements in many aspects; 18 1:7 1 breakthrough, rapidly developing into the frontier of materials science 19 Millerj.s. INORG.Chem, 2000; 39:4392
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