Spin Polarization at Organic-Ferromagnetic Interface: E ect of Contact Con guration

Based on ab initio theory, the interfacial spin polarization of a benzene-dithiolate molecule vertically adsorbed on a nickel surface is investigated by adopting di erent microscopic con-tact con gurations. The results demonstrate a strong dependence of the interfacial spin polarization on the contact con guration, where the sign of spin polarization may vary from positive to negative with the change of contact con guration. By analyzing the projected density of states, an interfacial orbital hybridization between the 3d orbital of the nickel atom and the sp3 hybridized orbital of the sulfur atom is observed. We also simulated the interfacial adsorption in mechanically controllable break junction experiments. The magne-toresistance obtained from Julliere model is about 27% based on the calculated interfacial spin polarization, which is consistent with experimental measurement.     

NO binds to unsaturated Os(IV) polyhydrides as a redox reagent

Reaction of Os(H)₃ClL₂(LPⁱPr₃) with equimolar NO occurs via a detectable paramagnetic species, to form OsCl(NO)L₂ + H₂, then Os(H)₂Cl(NO)L₂, together with the product of halogen transfer, OsHCl₂(NO)L₂. For comparison, equimolar NO and the dichloride Os(H)₂Cl₂L₂ react to give OsHCl₂(NO)L₂. DFT(PBE) calculations on potential radical intermediates reveal cases where spin density is on NO (vs. on Os), and show how coordinated H₂ can lead to the observed halogen transfer.     

Poly(1,8-octanediol citrate)/bioactive glass composite with improved mechanical performance and bioactivity for bone regeneration

Poly(1,8-octanediol-co-citrate)(POC) represents a new promising biocompatible and biodegradable polyester that has been extensively investigated for soft tissue engineering. However, the poor mechanical performance and poor bioactivity limit its application in bone regeneration. In this study, a series of POC/bioactive glasses(BG) composites were developed using 45 S5 Bioglass~ and a phytic acidderived bioactive glass(referred as PSC). The results indicated that calcium in BG could enhance the crosslinking of the POC/BG composites by forming calcium dicarboxylate bridges and thus improve their mechanical performances. When PSC were used, the composites exhibited significantly better mechanical properties compared to composites with 45 S5 Bioglass~. For example, by incorporating70 wt% PSC, the compressive strength of POC/PSC composites could be improved to approximately50 MPa and modulus 1.3±0.1 GPa. Furthermore, all these POC/PSC composites showed good in vitro bioactivity and cellular biocompatibility. Histology results in femoral condyle defects of Sprague-Dawley rats indicated that the POC/PSC samples integrated well with surrounding tissues and stimulated bone regeneration. The improved mechanical properties and bioactivity of POC/PSC composites make them promising for potential application in bone regeneration.     

Solution-processable precursor route for fabricating ultrathin silica film for high performance and low voltage organic transistors

In this paper, we introduce a simple solution spin-coating method to fabricate silica thin film from precursor route in the condition of low temperature and atmospheric environment, which possesses a low leakage current, high capacitance, and low surface roughness. With silica film (~ 50 nm), high performance and low voltage (< 4 V) p-/n-type organic transistors are fabricated. This method shows great potential for industrialization owing to its characteristic of low consumption and energy saving, time-saving and easy to operate.     

Influence of Poly (methyl metacrylate) Addition on Resistive Switching Performance of P3HT/P(VDF-TrFE) Blend Films

Organic semiconducting/ferroelectric blend films attracted much attention due to their elec-trical bistability and rectification properties and thereof the potential in resistive memory devices. Blend films were usually deposited from solution, during which phase separation oc-curred, resulting in discrete semiconducting phase whose electrical property was modulated by surrounding ferroelectric phase. However, phase separation resulted in rough surface and thus large leakage current. To further improve electrical properties of such blend films, poly(methyl metacrylate) (PMMA) was introduced as additive into P3HT/P(VDF-TrFE) semiconducting/ferroelectric blend films in this work. It indicated that small amount of PMMA addition could effectively enhance the electrical stability to both large electrical stress and electrical fatigue and further improve retention performance. Overmuch PMMA addition tended to result in the loss of resistive switching property. A model on the con-figuration of three components was also put forward to well understand our experimental observations.     

π-Electron-Assisted Relaxation of Spin Excited States in Cobalt Phthalocyanine Molecules on Au(111) Surface

We present our investigation on the spin relaxation of cobalt phthalocyanine (CoPc) films on Au(111) (CoPc/Au(111)) surface using scanning tunneling microscopy and spectroscopy. The spin relaxation time derived from the linewidth of spin-flip inelastic electron tunneling spectroscopy is quantitatively analyzed according to the Korringa-like formula. We find that although this regime of the spin relaxation time calculation by just considering the exchange interaction between itinerant conduction electrons and localized d-shells (s-d exchange interaction) can successfully reproduce the experimental value of the adsorbed magnetic atom, it fails in our case of CoPc/Au(111). Instead, we can obtain the relaxation time that is in good agreement with the experimental result by considering the fact that the π electrons in CoPc molecules are spin polarized, where the spin polarized π electrons extended at the Pc macrocycle may also scatter the conduction electrons in addition to the localized d spins. Our analyses indicate that the scattering by the π electrons provides an efficient spin relaxation channel in addition to the s-d interaction and thus leads to much short relaxation time in such a kind of molecular system on a metal substrate.     

Spin-glass-like magnetic ordering in Zn substituted magnetite magnetic fluids

Electron spin resonance (ESR) spectra of magnetic fluids involving polydispersed Zn(0.5)Fe(0. 5)Fe(2)O(4) (FZ5) and Zn(0.7)Fe(0. 3)Fe(2)O(4) (FZ7) nanomagnetic particles are scanned from 4.2 to 300K. The FZ7 fluid exhibits certain distinct features below 40K which are different from FZ5 fluid. These include (i) an isotropic shift in resonance field in zero-field-cooled ESR study, (ii) deviation of resonance field from sin(2)theta behavior (where theta is the angle between axis of the particle and field) in field cooled (FC) sample and (iii) abrupt increase in anisotropy field for FC sample. The results are analyzed in light of the core-shell model for nanomagnetic particles.     

Effect of Ta<Superscript>5+</Superscript> substitution for Mn on the ground state of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>

We report the charge state modification effects at the Mn site on the ground state properties of colossal magnetoresistive manganites. Ta⁵⁺ substitution results in an appreciable increase in the lattice parameters and unit cell volume due to increased Mn³⁺ concentration. The ferromagnetic-metallic ground state modifies to a cluster glass insulator for . The reduction in the transition temperatures with increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn³⁺ concentration and enhanced local structural effects, the local electrostatic potential of the substituent seems to contribute to the unusually strong reduction of the transition temperatures of the compounds. Thermo magnetic irreversibility just below Curie temperature (T_c), non-saturation of magnetization, two distinct magnetic transitions in ac susceptibility in an appropriate static field: close to T_c and other at low temperature (the spin freezing temperature (T_g)) and non-stationary dynamics with a characteristic maximum in the magnetic viscosity close to T_g confirm a cluster glass state for . These results find additional support from a linear low temperature magnetic specific heat of x = 0.10 with a characteristic broad maximum close to T_g.     

High resolution diffraction and small angle scattering neutron investigations of LaCo<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>O<Subscript>3+</Subscript><Subscript>δ</Subscript>: effect of oxygen content

We have investigated LaCo_0.5Mn_0.5O_{3+ δ} compounds with different oxygen content by means of magnetization, high resolution and small-angle neutron diffraction measurements. Oxygen content decrease down to stoichiometric composition leads to an essential increase of T_C and magnetic moment while Co/Mn ionic ordering degree is kept almost constant. It is assumed that upon oxygen reduction Co³⁺ ions change their valence state down to 2+ one that leads to dominating of Co²⁺-Mn⁴⁺ ferromagnetic interactions as well as T_C increase. Magnetic properties can be explained in terms of coexistence of long-range ferromagnetic order and short-range clusters with antiferromagnetic interactions prevailing. Size distribution of the mentioned short-range magnetic inhomogeneities is rather mild within the samples but it is strongly temperature dependent.     

自旋催化剂-量子触发化学反应

当初始态和过渡态之间存在能量差时,通常会考虑用催化的方法来增加反应速率,即经由能量更低过渡态的反应路径,或增加反应物初始态能量,如改变溶剂或在特殊表面吸附分子。然而,对于某些类型的反应,如H2和O2反应生成水, NO的氧化等,仅仅采用这些方法还不够,因为反应物和产物具有不同的自旋态,而自旋守恒定律一般会禁止该过程的发生。即使克服了能垒,该体系也不能转化成稳定的产物,且不改变其电子自旋多重态。但在特殊的非热力学条件下,该类反应仍可发生。这通常指自旋不守恒的过程。改变体系电子自旋最直接的方法是与原子核自旋有作用的电子自旋翻转。它可由自旋-轨道耦合来实现,因此,其实现的几率取决于元素的原子数。从3d金属开始,发生这种情况的可能性甚至更大。这是由于与d轨道耦合的效率更高所致,所以采用自旋交叉就能方便地解释自旋禁止反应发生的原因。然而,轻原子发生自旋翻转的可能性很低,因此,当面对无金属化学时,我们应该考虑自旋禁止反应发生的第二个方法—自旋催化。通过帮助克服自旋禁止的物质以促进化学反应,或通过顺磁催化剂诱导自旋解耦以降低活化能垒,这类现象就可定义为自旋催化。简而言之,为了得到想要的和热力学更有利的自旋态,一个反应粒子可以与自旋催化剂交换磁矩;该自旋催化剂需有拟自旋-简并基态或低激发态。因此,体系整个的自旋仍守恒,但可发生反应。值得强调的是,自旋“催化剂”指的是分子状态和固体状态,通常后者应用于工业中则方便得多。自旋催化是作为自旋化学的范例来研究的,或在外磁场中化学诱导动态核极化和反应,主要是指采用EPR光谱研究以液相为主的过程。本文简略介绍了自旋催化的理论。实际上,自旋催化与常规催化之间并不相互抵触—相同的材料既可作为自旋催化剂,也可用作常规催化剂,都起着降低反应能垒和提供自旋交换的自由基中心的作用。另外,许多现代材料包含着常规催化剂和自旋催化剂的特性。有些发生在多核磁性金属中心上的过程可能本身就包含着常规催化(活化底物)、自旋交叉(与d金属相互作用)和自旋催化(金属-氧簇合物中低能的铁磁-反铁磁转化)效应。气相自旋催化在实际应用中产生的主要问题是在稀释的体系中三粒子碰撞几率低,常规催化在这方面则有很多优势。我们首先列出固体成为自旋催化剂的条件：(1)活性中心中至少2个自旋态的能量差要小于反应温度下热运动的能量,这样无需额外的能量活化催化剂;(2)较大的比表面积以提供更多的自旋中心用于相互作用;(3)最好能够自旋导电,在此情况下反应无需三粒子碰撞即可发生。这是因为自由基可通过催化剂的电子系统交换自旋,使得自旋-自旋相互作用的几率迅速增加,从而有利于自旋催化反应的进行。另外,如果固体或载体具有自旋导电性,则无需外加电场或磁场,即有可能遥控催化中心的电荷和自旋态,从而避免使用外电场或磁场。实际上,许多反应过程本身就包含着自旋催化,它还可使反应过程的许多不足变成优势,如对于不需要的链式自由基反应;通过引入自旋捕获剂使得自旋禁止反应成为有用的自旋催化;磁性粒子的浓度以及外加磁场和电场均可导致自旋催化/禁止反应。由于均相自旋催化的研究较早,在此不再赘述。本文详细介绍了多相体系中的自旋催化的应用,如燃烧、温和氧化、环化、开环、非极性小分子的活化和不稳定自由基的耦合等。可能用作自旋催化剂的材料有：含有不同顺磁性的金属离子的磁性氧化物或多核磁性簇合物;嫁接在一些载体上的多核络合物或过渡金属(低温催化);带有非整数氧化价态的导电金属;各种具有半金属性和导电性的碳材料。研究自旋催化反应的一个突出问题就是这些过程大部分是自由基式的,趋于非线性区域,因而很难预测,也没有一个便利的工具用以描述,甚至预测自旋催化反应,但也许这些研究的特点就是不可预测性。自旋催化除了可调变反应的进行,我们还可从中获得一个独特的调节手段：通过外加磁场或电场触发基元过程,在非热力学上控制反应的进行。该手段在控制化学反应方面具有明显优势,因为现在大都是通过调节温度、压力和流量等参数来实现对化学反应的控制,且滞后严重。同时,通过添加外加磁场可立刻改变反应速率。另外,通过降温可精细控制基元反应,从而开辟了一种抑制副反应的方法,因而也使得反应的随机性降低。