Ab initio/MBPT Studies of the Effective Exchange Integrals and Theoretical Models of Organic Ferromagnets

Nowadays the studies of organize ferromagnets have been becoming a very attractive area of material science in both theoretical and experimental aspects. A major theoretical problem on design of OFM is to estimate the effective exchange integrals(J) between radical sites. However, most of theoretical work was on hypothetical hydrocarbons, which were impracticable in the synthesis. The recent breakthrough in the synthesis of OFM turns the theorist’s attention to some more realistic models such as those

Tunneling magnetoresistance in ferromagnet/organic-ferromagnet/metal junctions

Spin-dependent transport in ferromagnet/organic-ferromagnet/metal junctions is investigated theoretically.The results reveal a large tunneling magnetoresistance up to 3230%by controlling the relative magnetization orientation between the ferromagnet and the central organic ferromagnet.The mechanism is explained by distinct efficient spin-resolved tunneling states in the ferromagnet between the parallel and antiparallel spin configurations.The key role of the organic ferromagnet in generating the large magnetoresistance is explored,where the spin selection effect is found to enlarge the difference of the tunneling states between the parallel and antiparallel configurations by comparing with the conventional organic spin valves.The effects of intrinsic interactions in the organic ferromagnet including electron–lattice interaction and spin coupling with radicals on the magnetoresistance are discussed.This work demonstrates a promising potential of organic ferromagnets in the design of high-performance organic spin valves.

Spin-excited states and rectification in an organic spin rectifier

Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent trans- mission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.

Length dependence of rectification in organic co-oligomer spin rectifiers

The rectification ratio of organic magnetic co-oligomer diodes is investigated theoretically by changing the molecular length. The results reveal two distinct length dependences of the rectification ratio： for a short molecular diode, the chargecurrent rectification changes little with the increase of molecular length, while the spin-current rectification is weakened sharply by the length; for a long molecular diode, both the charge-current and spin-current rectification ratios increase quickly with the length. The two kinds of dependence switch at a specific length accompanied with an inversion of the rectifying direction. The molecular ortibals and spin-resolved transmission analysis indicate that the dominant mechanism of rectification suffers a change at this specific length, that is, from asymmetric shift of molecular eigenlevels to asymmetric spatial localization of wave functions upon the reversal of bias. This work demonstrates a feasible way to control the rectification in organic co-oligomer spin diodes by adjusting the molecular length.

Effect of interfacial coupling on rectification in organic spin rectifiers

The effect of interfacial coupling on rectification in an organic co-oligomer spin diode is investigated theoretically by considering spin-independent and spin-resolved couplings respectively. In the case of spin-independent coupling, an optimal interfacial coupling strength with a significant enhanced rectification ratio is found, whose value depends on the structural asymmetry of the molecule. In the case of spin-resolved coupling, we found that only the variation of the interfacial coupling with specific spin is effective to modulate the rectification, which is due to the spin-filtering property of the central asymmetric magnetic molecule. A transition of the spin-current rectification between parallel spin-current rectification and antiparallel spin-current rectification may be observed with the variation of the spin-resolved interfacial coupling. The interfacial effect on rectification is further analyzed from the spin-dependent transmission spectrum at different biases.

Bis-radicals (nitronyl nitroxide and imino nitroxide) Substituted Benzene with Long Alkyl Chain: Synthesis, Magnetic Study and Formation of LB film

The titled compound 1 as well as compounds 2 and 3 with similar chemical structures were prepared and characterized. The magnetic properties of 1 were investigated with SQUID (MPMS, quantum design) magnetometer. Studies with Langmuir-Blodgett (LB) technique indicated that stable condensed film of 1 could be formed at air-water interface and could be transferred onto various solid substrate under suitable conditions.

Crystal Structure of trans－2－（1－Naphthyl）－1－（p－（4＇，4＇，5＇，5＇－tetramethyl－4＇，5＇－dihydro－1＇H－imidazolyl－1＇－oxy－3＇－oxide）－phenyl）－imine，C_（24）H_（24）N_3O_2

The crystal structure of the title compound was determined by X-ray diffraction method at room temperature.The crystal belongs to triclinic space group P1 with the following crystallographic parameters:a=13.942(2),b=15.540(2),c=10.007(1) A,a=105.16(1)°,β=92.42(1)°,γ=88.12(1)°,V=2090.2(4) Z=4,Dc=1.23g cm-3,F(000)=820,μ(MoKα)=0.74 cm-1,and final R= 0.054 for 3208 observations.Two molecules , which are slightly different in conformation,coexist in an asymmetric unit. Some intermolecular distances are fairly short.The packing arrangement of the molecules in the crystal is also discussed.

PREPARATION AND MAGNETIC PROPERTIES OF POLYMERIC COMPLEXES CONTAINING 1,10-PHENANTHROLINE

A series of polymeric complexes were prepared from Fe^2＋, Co^2＋ or Ni^2＋ and poly（Schiff base） （DAPcIPA）, which was obtained by polycondensation of 5,6-diamino-1,10-phenanthroline （DAP） with isophthalaldehyde （IPA）. The structures of the polymer and the polymeric complexes were characterized by IR, 1^H-NMR and elemental analysis. The magnetic behavior of these complexes was measured as a function of magnetic field strength （0-3.98 ~ 106 A/m） at 5 K and as a function of temperature （5-300 K） at a magnetic field strength of 2.39 × 10^6 A/re. Experimental results show that DAPcIPA-Ni^2＋, DAPcIPA-Co^2＋ are soft ferromagnets while DAPcIPA-Fe^2＋ exhibits features of an antiferromagnet.