From Low to High Saturation Magnetization in Magnetite Nanoparticles: The Crucial Role of the Molar Ratios Between the Chemicals.

In this study, a comprehensive characterization of iron oxide nanoparticles synthesized by using a simple one-pot thermal decomposition route is presented. In order to obtain monodisperse magnetite nanoparticles with high saturation magnetization, close to the bulk material, the molar ratios between the starting materials (solvents, reducing agents, and surfactants) were varied. Two out of nine conditions investigated in this study resulted in monodisperse iron oxide nanoparticles with high saturation magnetization (90 and 93% of bulk magnetite). The X-ray diffraction analyses along with the inspection of the lattice structure through transmission electron micrographs revealed that the main cause of the reduced magnetization in the other seven samples is likely due to the presence of distortion and microstrain in the particles. Although the thermogravimetric analysis, Raman and Fourier transform infrared spectroscopies confirmed the presence of covalently bonded oleic acid on the surface of all the samples, the particles with higher polydispersity and the lowest surface coating molecules showed the lowest saturation magnetization. Based on the observed results, it could be speculated that the changes in the kinetics of the reactions, induced by varying the molar ratio of the starting chemicals, can lead to the production of the particles with higher polydispersity and/or lattice deformation in their crystal structures. Finally, it was concluded that the experimental conditions for obtaining high-quality iron oxide nanoparticles, particularly the molar ratios and the heating profile, should not be chosen independently; for any specific molar ratio, there may exist a specific heating profile or vice versa. Because this synthetic consideration has rarely been reported in the literature, our results can give insights into the design of iron oxide nanoparticles with high saturation magnetization for different applications.

Magnetic order and competition with superconductivity in (Ho-Er)Ni2B2C.

The rare earth magnetic order in pure and doped Ho(1-x)ErxNi2B2C (x = 0, 0.25, 0.50, 0.75, 1) single crystal samples was investigated using magnetization and neutron diffraction measurements. Superconducting quaternary borocarbides, RNi2B2C where R = Ho, Er , are magnetic intermetallic superconductors with the transition temperatures~10 K in which long range magnetic order develops in the same temperature range and competes with superconductivity. Depending on the rare earth composition the coupling between superconductivity and magnetism creates several phases, ranging from a near reentrant superconductor with a mixture of commensurate and incommensurate antiferromagnetism to an incommensurate antiferromagnetic spin modulation with a weak ferromagnetic component. All of these phases coexist with superconductivity. RKKY magnetic interactions are used to describe the magnetic orders in the pure compounds. However, the doping of Er on Ho sites which have two strong magnetic moments with two different easy directions creates new and complicated magnetic modulations with possible local disorder effects. One fascinating effect is the development of an induced magnetic state resembling the pure and doped R2CuO4 cuprate with R = Nd and Pr.

Publisher Correction: Magnetization Manipulation of a Flexible Magnetic Sensor by Controlled Stress Application.

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Magnetization Manipulation of a Flexible Magnetic Sensor by Controlled Stress Application.

Spin-based electronic devices on polymer substrates have been intensively investigated because of several advantages in terms of weight, thickness, and flexibility, compared to rigid substrates. So far, most studies have focused on maintaining the functionality of devices with minimum degradation against mechanical deformation, as induced by stretching and bending of flexible devices. Here, we applied repetitive bending stress on a flexible magnetic layer and a spin-valve structure composed of Ta/NiFe/CoFe/Cu/Ni/IrMn/Ta on a polyimide (PI) substrate. It is found that the anisotropy can be enhanced or weakened depending upon the magnetostrictive properties under stress. In the flat state after bending, due to residual compressive stress, the magnetic anisotropy of the positive magnetostrictive free layer is weakened while that of the pinned layer with negative magnetostriction is enhanced. Thus, the magnetic configuration of the spin-valve is appropriate for use as a sensor. Through the bending process, we design a prototype magnetic sensor cell array and successfully show a sensing capability by detecting magnetic microbeads. This attempt demonstrates that appropriate control of stress, induced by repetitive bending of flexible magnetic layers, can be effectively used to modify the magnetic configurations for the magnetic sensor.

Transfer printing of metal nanoring and nanodot arrays for use in catalytic reactions.

Nanoscale metal ring and dot catalyst arrays are printed over large substrate areas using vertically aligned carbon-based stamps with the ring- and dot-shaped tips. The fundamental nature of these ring and dot catalysts is successfully compared by applying them in diverse electrocatalytic reactions in acidic and alkaline media.

Printable nanoscale metal ring arrays via vertically aligned carbon nanotube platforms.

This paper reports a novel and efficient strategy for fabricating sub-100 nm metal ring arrays using a simple printing process. Vertically aligned carbon nanotubes that are supported by hexagonally ordered channels of alumina matrices are used as a stamp to print nanoscale ring patterns, which is a very unique stamping platform that has never been reported. Using this strategy, uniform nanoring patterns of various metals can be directly printed onto a wide range of substrate surfaces under ambient conditions. Significantly, the size and interval of the printed nanorings can be systematically tuned by controlling the ring-shaped tip dimensions of the pristine stamps. An advanced example of these printable nanoscale metal ring arrays is explicitly embodied in this work by investigation of the plasmon resonances of metal nanorings with different sizes and intervals.

Syntheses, structures, and magnetic characterizations of cyanide-bridged Fe(III)Mn(III) chains constructed by mer-Fe(III)tricyanide and Mn(III) Schiff bases: magnetostructural relationship.

Five Fe(III)Mn(III) bimetallic compounds [Fe(iqc)(CN)(3)][Mn(5-Xsalen)]·pMeOH·qMeCN·rH(2)O [Hiqc = N-(quinolin-8-yl)isoquinoline-1-carboxamide; salen = N,N'-ethylenebis(salicylideneiminato) dianion; X = H(2), F(3, 3a), Cl(4), Br(5)] were prepared by assembling a newly designed mer-Fe tricyanide (Ph(4)P)[Fe(iqc)(CN)(3)]·0.5H(2)O (1) and the respective Mn Schiff bases Mn(5-Xsalen)(+). Compounds 2-4 show linear chain structures in which trans-positioned cyanides of the Fe precursor bridge neighbouring Mn atoms, while 5 is a zigzag chain coordination polymer where two cyanide groups of the precursor in the cis mode act as bridges. The structural change from linear to zigzag may arise from the size effect of the halogens. The reversible structural transformation occurs between 3 and 3a upon the solvation-desolvation protocol and the corresponding magnetic behaviours are affected. Furthermore, in 4 and 5, the helical chains are established through hydrogen bonding of solvent molecules. From a magnetostructural point of view, within the linear chain system, the ferromagnetic coupling in 2, contrary to antiferromagnetic interactions in 3-4, is associated with the large torsion angle of C(eq)-Fe-Mn-N(O)(eq) (eq = equatorial) as well as almost the linear Mn-N≡C angle.

Printing of sub-100-nm metal nanodot arrays by carbon nanopost stamps.

This work reports an efficient method to fabricate hexagonally patterned metal nanodot arrays at the sub-100-nm scale, which is based on contact printing via novel nanometer-scaled stamps. Vertically aligned carbon nanoposts, supported by hexagonally ordered nanochannels of anodic aluminum oxide templates, are employed as the stamping platform to directly transfer controlled metal nanodot arrays. Using the fabrication platform, a number of patterned metal nanodot arrays made of Au, Cu, Ni, Ag, Pt, Al, and Ti can be contact-printed over large substrate areas in ambient conditions. The size, density, and interdistance of the printed nanodots are controllable with a tight correspondence to the mother stamp geometries, which can be precisely tuned by modifying the pore dimensions of the alumina matrixes. An advanced example of contact printing of metal nanoparticles is successfully demonstrated by the controlled formation of nanodot arrays in a specific area.

Diameter-engineered SnO2 nanowires over contact-printed gold nanodots using size-controlled carbon nanopost array stamps.

A novel and effective methodology to control the diameters of semiconductor nanowires is reported through a versatile contact-printing method for obtaining size-controlled nanocatalysts by size-tunable carbon-based nanometer stamps. Vertically aligned carbon nanopost arrays, derived from nanoporous alumina templates, are used as the nanoscale stamps for printing of catalyst nanoparticles. The diameter of the carbon nanopost can be engineered by adjusting the pore dimension of the templates. Over the contact-printed Au nanodots in a uniform size distribution, semiconductor SnO2 nanowires are grown via a vapor-liquid-solid growth mechanism. Consequently, a direct dimension correspondence is achieved between the carbon nanopost stamp, the printed Au catalyst, and the finally obtained SnO2 nanowires. A model example of the diameter-dependent electrical properties of the semiconductor nanowires is successfully demonstrated in this work by applying three diameter-controlled SnO2 nanowires to nanowire field effect transistors.

One-dimensional cyanide-bridged Mn(III)W(V) bimetallic complexes: metamagnetism, spontaneous resolution, and slow magnetic relaxation.

The reaction of [W(CN)(6)(bpy)](-) with the corresponding Mn Schiff bases led to the formation of two antiferromagnetic (1) and ferromagnetic (2) chains. The formation of the conglomerate (2) is associated with chiral induction by the enantiomeric chelate-ring conformation of the Mn Schiff base. Modulation of the linking groups in the Mn Schiff bases affects the interchain contacts, causing alteration of the magnetic behaviors from metamagnetism (1) to slow magnetic relaxation (2).

Syntheses, crystal structures and magnetic properties of cyano- and phenoxide-bridged Fe(iii)Mn(iii) tetramers containing fac-Fe(iii) tricyanides and Mn(iii) Schiff bases.

Three cyanide-linked Fe(iii)Mn(iii) bimetallic clusters, [(Tp)Fe(CN)(3)](2)[Mn(acphen)](2) [; acphen = N,N'-ethylenebis(2-hydroxyacetophenylideneiminato) dianion], [(Tp)Fe(CN)(3)](2)[Mn(5-Bracphen)](2) [; 5-Bracphen = N,N'-ethylenebis(5-bromo-2-hydroxyacetophenylideneiminato) dianion], and [(Tp)Fe(CN)(3)](2)[Mn(salen)](2).6H(2)O [; salen = N,N'-ethylenebis(salicylidineiminato) dianion], were prepared by self-assembling a facial [(Tp)Fe(CN)(3)](-) [Tp = hydrotris(pyrazolyl)borate] precursor and respective Mn(iii) Schiff bases. X-Ray crystal structure analyses revealed that each complex is composed of a central Mn(iii) dimer doubly linked by phenoxides of the tetradentate N(2)O(2) Schiff bases and the terminal [(Tp)Fe(CN)(3)](-) groups connecting to the center through cyanides. Using the spin Hamiltonian H = -2J(1)(S(Fe1).S(Mn1) + S(Mn1a).S(Fe1a)) - 2J(2)(S(Mn1).S(Mn1a)), where J(1) stands for the exchange coupling constant between Fe(iii) (S(Fe) = 1/2) and Mn(iii) (S(Mn) = 2) through cyanides and J(2) between Mn(iii) ions via phenoxides, the best fits corresponded to J(1) = 2.61 cm(-1) and J(2) = 0.85 cm(-1) for , J(1) = 2.50 cm(-1) and J(2) = 1.30 cm(-1) for , and J(1) = -2.15 cm(-1) and J(2) = 0.55 cm(-1) for . The phenoxide routes transmit ferromagnetic interactions in all cases, while ferromagnetic or antiferromagnetic couplings occur through the cyanide linkage. Although the geometric parameters relevant to the magnetic Fe-C[triple bond, length as m-dash]N-Mn pathways are analogous to each other their magnetic natures are varied across the compounds, which supports that a degree of orbital overlap is quite sensitive to a subtle structural change in the present system.

Cyanide-bridged Fe(III)-Mn(III) bimetallic complexes with dimeric and chain structures constructed from a newly made mer-Fe tricyanide: structures and magnetic properties.

Four cyanide-linked Fe(III)-Mn(III) complexes were prepared by reacting Mn Schiff bases with a new molecular precursor (PPh(4))[Fe(qcq)(CN)(3)] [1; qcq = 8-(2-quinolinecarboxamido)quinoline anion]. They include a dimeric molecule, [Fe(qcq)(CN)(3)][Mn(3-MeOsalen)(H(2)O)] x 2 H(2)O [2 x 2 H(2)O; 3-MeOsalen = N,N'-ethylenebis(3-methoxysalicylideneiminato) dianion], and three 1D zigzag chains, [Fe(qcq)(CN)(3)][Mn(5-Clsalen)] x 3 H(2)O [3 x 2 MeOH; 5-Clsalen = N,N'-ethylenebis(5-chlorosalicylideneiminato) dianion], [Fe(qcq)(CN)(3)][Mn(5-Brsalen)] x 2 MeOH [4 x 2 MeOH; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylideneiminato) dianion], and Fe(qcq)(CN)(3)][Mn(salen)].MeCN x H(2)O [5 x MeCN; salen = N,N'-ethylenebis(salicylideneiminato) dianion]. The complexes consist of extensive hydrogen bonding and pi-pi stacking interactions, generating multidimensional structures. Magnetic studies demonstrate that antiferromagnetic couplings are operative between Fe(III) and Mn(III) centers bridged by cyanide ligands. On the basis of an infinite chain model, magnetic coupling parameters of 2-5 range from -9.3 to -14.1 cm(-1). A long-range order is observed at 2.3 K for 3 and 2.2 K for 4, while compound 5 shows spin glass behavior possibly coupled with magnetic ordering.