Cr/Ru/PtCo/Ru/PtCo/Ru介质中底层Ru厚度对磁记录特性影响的研究

讨论了Cr/Ru（1）/PtCo（稳定层）/Ru（2）/PtCo（记录层）/Ru（3） 结构的矫顽力Hc_c与层间反铁磁耦合交换场Hex_ex随Ru（1）与Ru（2）厚度变 化的规律.研究发现 ，样品的矫顽力及交换场随Ru（1）厚度增加而增大， 这可能是由Ru（1）hcp结构引起的. 矫顽力及交换场在Ru（2）厚度为08nm处有峰值. 关键词： 磁记录 反铁磁耦合     

混合桥基双核配合物中的轨道互补与反互补效应

在混合桥基的双核体系中,金属中心的磁轨道的线形组合可与相同对称性的桥基最高占据轨道(HOMO'S)相互作用.如果两种桥联配体稳定同一磁轨道组合,则称它们以互补方式起作用;反铁磁偶合就会被加强.反之,如果桥联配体稳定不同的磁轨道组合,则称它们以反互补方式起作用;这将减小反铁磁偶合.本文就互补和反互补效应以及相关的磁学知识做一简要概述.     

对称三唑Schiff碱与铜的配合物合成及性能

合成了４种新型对称三唑水杨醛Ｓｃｈｉｆ碱的铜配合物［ＣｕＬ１Ｃｌ２］（Ⅰ）和三核配合物［Ｃｕ３（Ｌ２－Ｌ４）２Ｃｌ４］·ｎＨ２Ｏ（Ⅱ～Ⅳ），其中Ｌ１，Ｌ２，Ｌ３和Ｌ４分别为４－氨基－１，２，４－三唑、４－氨基－３，５－二甲基－１，２，４－三唑、４－氨基－３，５－二乙基－１，２，４－三唑和４－氨基－３，５－二羟甲基－１，２，４－三唑的水杨醛Ｓｃｈｉｆｆ碱．经元素分析、电导、红外光谱、热重分析、电子光谱、ＥＳＲ和变温磁化率表征，该类配合物为畸变四方构型．配合物Ⅱ的变温磁化率表明，铜离子间存在弱的反铁磁相互作用，Ｊ＝－１８．９ｃｍ－１，ｇ＝２．０８，Ｆ＝２．７×１０－３．配合物对Ｂ细胞增殖有抑制作用．     

Magneto-structural characterization of metallocene-bridged nitronyl nitroxide diradicals by X-Ray, magnetic measurements, solid-state NMR spectroscopy, and ab initio calculations

Crystallization of ferrocene and ruthenocene substituted in the 1- and 1'-positions by two nitronyl nitroxide radicals gave the new crystal phases beta-1 (besides the known phase alpha-1), alpha-2, and beta-2 whose structures were determined by X-ray analysis. In beta-1 the radical moieties adopt transoid positions, whereas two different cisoid conformations are adopted by alpha-2 and beta-2. These conformations result from inter- and intramolecular hydrogen bonds, respectively. All compounds experience antiferromagnetic interactions, and J/k(B) values up to -7 K have been found by fitting the experimental magnetic susceptibilities to a modified Bleaney-Bowers equation. The solid diradicals alpha-1, beta-1, alpha-2, and beta-2 as well as the ferrocene 3, which was substituted by a unique nitronyl nitroxide, were investigated by (13)C and (1)H NMR spectroscopy with magic angle spinning. The carbon signals cover a range of 2000 ppm, and are well resolved such that the structure could be confirmed. Conversion of the signal shifts into spin densities disclosed the mechanisms by which spin delocalization from the nitronyl nitroxide substituents to the metallocene core occurs. The spin density distribution in alpha-1, beta-1, and 3 was also predicted by DFT calculations. There is good agreement between the experimental and theoretical trends of the spin delocalization. The magnetic interactions were discussed in the light of intramolecular spin transfer and its dependence on geometric constraints, demonstrating that the 1,1'-metallocenylene bridge is not a robust magnetic coupler.     

Hydrostatic pressure induced transformation of magnetism in a trimetallic CuMnFe Prussian blue analogue

With chemical co-precipitation, trimetal Prussian blue analogue Cu_0.71Mn_0.79[Fe(CN)₆]·7.3H₂O was obtained. We used supercritical carbon dioxide extraction apparatus to pressurize the samples for 10?MPa, 20?MPa, and 42?MPa for 5?h. X-ray powder diffraction data show the single-phase of the sample at different pressures with a NaCl-type face-centered cubic structure. Trimetal Prussian blue analogs Cu_0.71Mn_0.79[Fe(CN)₆]·7.3H₂O include both ferromagnetic and antiferromagnetic exchange interactions among different metal ions and exhibit novel mixed magnetic property. Hydrostatic pressure may be a powerful tool for development of new functional magnets. Spontaneous magnetization in the field cooled (FC) magnetization above 10?MPa approaches a value three times larger than that at 1?atm, and the zero field cooled (ZFC) magnetization is also extremely sensitive to pressure. The results show that pressure can simultaneously enhance the ferromagnetic and antiferromagnetic interactions in this material. The Weiss constant decreases gradually with pressure increasing from 10 to 42?MPa, due to pressure-induced electron transfer from Mn²⁺/Cu²⁺ to Fe³⁺.     

Dielectric and Magnetic Relaxations Exhibited in a 2D Parallel Interpenetrating Frustrated Star Net

Constructing multiple functional geometric frustration magnets is a hot topic in solid state chemistry and material science. Herein, a two-dimensional (2D) parallel interpenetrating “star” net complex [HDMPDA][Fe₆(μ₃-O)₂(μ-O₂CH)₁₅] ( 1 ) was obtained successfully with HDMPDA (DMPDA=N, N’-dimethyl-1,3-propanediamine) as charge balancer. The dipole reorientation of the rotator [HDMPDA]⁺ in the complex brings a structure transition which leads dielectric relaxation close to room temperature. Despite strong antiferromagnetic coupling existing between ions in the net, long-range order temperature T_N of the complex is suppressed to 4.2 K by geometric frustration. Interestingly, below T_N, a canted antiferromagnetic state, accompanied with slow magnetic relaxation, is detected due to the lack of enough magnetic coupling between 2D layers. Thus, 1 is a particular multifunctional magnetic frustration material containing two different types of relaxations.     

锰基高温反铁磁形状记忆合金中马氏体逆相变的表面浮突研究

本文利用原子力显微镜原位研究Mn_79.5Fe_15.6Cu_4.9反铁磁高温形状记忆合金在升降温过程中与马氏体相变相关的表面起伏特征, 同时采用X射线衍射、动态热机械分析等实验检测手段辅助分析其微观组织结构演化, 从纳米尺度分析面心立方–面心四方结构相变及表面浮突产生的物理机理. 实验结果表明: 在升降温过程中观察到帐篷型表面浮突, 由面心立方–面心四方马氏体逆相变产生的, 即母相浮突, 这与通常观测到的马氏体浮突不同; 实验证实面心立方–面心四方马氏体逆相变具有切变特征, 马氏体孪晶的逆向切变是产生帐篷型表面浮突的主要机理; 测得逆孪晶切变的浮突角小于1°, 远小于传统形状记忆合金的表面浮突角值, 这是由于面心立方母相与面心四方马氏体相结构差异较小造成的; 表面浮突随温度变化具有极好的可逆性, 这是马氏体相变晶体学可逆性决定的, 表明该合金具有优良的表面形貌记忆效应.     

金属离子掺杂对CuO基纳米复合材料的交换偏置调控

为了研究反铁磁基体中掺杂的金属离子对交换偏置效应的影响, 本文采用非均相沉淀法制备了纳米复合材料. X射线衍射图(XRD)和场发射扫描电子显微镜(SEM) 照片清晰表明CuO纳米复合样品具有统一的颗粒尺寸, 约为80 nm. 通过体系中掺杂磁性金属离子Ni和Fe, 实现了亚铁磁MFe₂O₄ (M=Cu, Ni)晶粒镶嵌在反铁磁(AFM) CuO 基体中. 在CuO基体中加入少量的Ni能改变两相交界面的磁无序从而生成类自旋玻璃相, 相应提高对铁磁相磁矩的钉扎作用. 同时, 场冷过程中反铁磁相内形成磁畴, 冻结在原始状态或磁场方向上, 畴壁也起到钉扎铁磁自旋的作用, 进而提高交换偏置效应. 随后加入的Ni 会生成各向异性能较大的NiO, 也能够提高交换偏置场. 在带场冷却下, 所有样品均发生垂直交换偏置, 也证明了样品在场冷过程中形成了自旋玻璃相, 正是由于亚铁磁与自旋玻璃相界面上的磁交换耦合, 才导致回线在整个测量范围内发生了向上偏移. 零场冷却和场冷却(ZFC/FC)情况下磁化强度与温度变化曲线(M-T)说明在这些复合材料中的交换偏置效应是由于存在亚铁磁颗粒和类自旋玻璃相界面处的交换耦合作用. 研究发现随着持续掺杂Ni离子, 交换偏置场先缓慢增加后又急剧增加, 生成各向异性能高的反铁磁相NiO 和反铁磁相内的畴态组织是这一结果的原因.     

A Cu(II) Complex with IM-MeImz-κ~2 N,O Mode in [Cu(IM-MeImz)_2]·(SCN)_2: Synthesis, Crystal Structure and Magnetic Properties

A new copper(II) compound with imino nitroxide radicals [Cu(IM-MeImz)2]?(SCN)2 (IM-meImz =2-(5-methylimidazol-4-yl)-4,4,5,5-tetramethyl-2-imidazoline-1-oxyl) has been synthesized and characterized structurally and magnetically. It crystallizes in monoclinic, space group P21/c with a = 9.3604(7), b = 10.3012(7), c = 16.6684(12) , β = 105.0290(10)o, V = 1552.25(19) 3, C24H34CuN10O2S2, Mr = 622.27, Z = 2, Dc = 1.331 g/cm3, μ(MoKα) = 0.876 mm-1, F(000) = 650, the final R = 0.0374 and wR = 0.1079. X-ray analysis demonstrates that the IM-MeImz ligand is coordinated to the copper(II) ion as an unusual didentate chelate with a κ2 N(MeImz),O(IM) mode in the complex. The square-planar coordination sites at Cu(II) are occupied by two O and two N atoms from the imino nitroxide radicals. The complex molecules are connected as a onedimensional polymer structure by intermolecular interactions. Magnetic measurements show that there are intramolecular antiferromagnetic interactions between the Cu(II) ion and radicals.