Magnetic Properties Of Molecular Magnets Based On 3d-4f Complexs By Cyanide Ligand

Cyano-bridged complexes have been widely studied in many fields,particularly have shown magnetic properties with high Tc values and magnetic-optical phenomenon. These studies were mainly focus on transition metals. Until recently, the studies about magnetic properties of 3d-4f molecular complexes are very scarce. The major difficulties in studying the magnetic properties of the 3d-4f molecular complexes arise from the well-shielded 4f electrons of rare earth ions, except for Gd3+, has a frist-order angular momentum, which prevents the use of a spin-only Hamiltonian for isotropic exchange.The joint effect of the electrostatic crystal field and orbital comtribution can result in an important anisotropy of the magnetic susceptibility and exchange interaction. Recently, Using betaine, N,N-dimethylformamide(DMF) as hybrid ligand, many 3d-4f Cyano-bridged complexes have been synthesized and the crystal structures and magnetic properties of these complexes have been determined. Cyano-bridged 3d-4f complexes have attracted great attention because of their rich and interesting structures,and particular optical properties and magnetic properties with their potential application. the research of these complexes has been one of the most attractive interdiscipline of physical, chemistry and material science. In the thesis, the magnetic measurements and proved microsurements are performed to study the magnetic properties in cyano-bridged 3d-4f complexes. In the thesis, we have obtained the results in the following aspects:1. The magnetic properties of three cyano-bridged heterodinuclear 3d-4d complexes [Ln(H2O)3(DMF)4(μ-CN)Fe(CN)5]-nH2O(Ln=Nd,Gd,Er) investigated in detail in 100Oe dc field. Their curie temperatureθ< 0 was obtained by extrapolating the linear portion ofχm-1 versus T toχm-1= 0.The negative value of 0 indicates the presence of antiferromagnetic ordering. the magnetic susceptibilities of the complexes [GdFe] and [ErFe] follow Curie-Weiss law in the temperature range 1.9-300K. the magnetic susceptibilities of the complexes [NdFe] deviate from the Curie-Weiss law below 50K, which is caused by Zeeman effect contributions of the gound states of Nd. magnetic susceptibilities data were fit for complexes [LnFe] on the Hamiltonian H= JS1S2+β(S1g1+S2g2)H. the magnetic parameters J of complexes [NdFe], [GdFe] and [ErFe] fit to the experimental data are-48.4cm-1,-0.44cm-1,-6.06cm-1, respectively.the value of J were infulenced mainly by the nonlinear structure of magnetic moment of Ln ions. the results have confirmed that the spin coupling between Ln and Fe ions through an cyano group in complexes [LnFe] is antiferromagnetic.2. The magnetic properties of two cyano-bridged 3d-4f bimetal LnFe(CN)6·4H2O (Ln=Sm3+, Gd3+) investigated in detail in 10Oe and 100Oe dc field. curie temperatureθ< 0 of [GdFe] was obtained by extrapolating the linear portion ofχm-1 versus T to Xm-1=0-The negative value of 0 indicates the presence of antiferromagnetic ordering.the magnetic susceptibilities of the complexes [NdFe] deviate from the Curie-Weiss law,which is caused by first-and second-order Zeeman effect contributions of the gound and first excited states of Sm ions. The relationship ofχmT vs T have the same trend with complexes [NdFe] and [GdFe]. Molecular-field theory succeeds in explaining the trend. In complexes [LnFe], the results have confirmed that the spin coupling between Ln and Fe ions is antiferromagnetic. Since Sm3+/Gd3+ ions have large moments and Sm3+/Gd3+ separations are are rather small, the spin interactions between Sm3+/Gd3+ ions should not be ignored, the spin coupling between Ln and Ln ions is ferromagnetic.the magnitudes of the two coupling are very near at low temperature. the combination of these interactions lead eventually to the ferrimagnetic ordering.Eventually, we summarize the work of the paper and envisage the coming study of the 3d-4f molecular complexes...