We implemented a nuclear magnetic resonance (NMR) study on rubrene(C42H28)-Co nano-composites that exhibit an enhanced magnetoresistance (MR) ratio of 80%. The 59Co NMR spin echo experiment enabled clarification of the hyperfine field of Co at the interface between the ferromagnet and the molecules, which has not been investigated for molecular spintronics. An enhanced hyperfine field of the Co was observed in the rubrene-Co nano-composites, which may be related to the enhancement of the MR ratio. This study demonstrates the importance of microscopic investigation of the interface between molecules and ferromagnets that governs spin-dependent transport in molecular spin devices.
Cobalt ferrite nanoparticles have been synthesized using a co-precipitation approach. Co:Fe precursor ratio is varied over a certain window (1.05 to 1.2). It is observed that the 1.15:2 precursor ratio gives better phase control but poor coercivity. On the other hand, 1.05:2 precursor ratio results in substantially better coercivity values (274kA/m; almost 300% the value reported for co-precipitated cobalt ferrite by Praveena et al.), but moderate BH product maximum (2.25 kJ/m3; ~ comparable to many reports on cobalt ferrite nanoparticles so far). The nanoparticles with best coercivity are ann…
In this work, a successful synthesis of magnetic cobalt ferrite (CoFe2O4) nanoparticles is presented. The synthesized CoFe2O4 nanoparticles have a spherical shape and highly monodisperse in the selected solvent. The effect of different reaction conditions such as temperature, reaction time and varying capping agents on the phase and morphology is studied. Scanning transmission electron microscopy showed that the size of these nanoparticles can be controlled by varying reaction conditions. Both X-ray diffraction and energy dispersive X-ray spectroscopy corroborate the formation of CoFe2O4 spine…
We present a comparative study on the influence of applied magnetic field on the resistance of $C_{1-x}Co_x$ thin films (with $x=0.1$, $0.15$ and $0.2$) grown on $Si$ substrate by pulsed laser deposition technique. It is found that the behavior of magnetoresistance (MR) drastically depends on the temperature. Namely, at low temperatures MR is positive and its behavior is governed by the field mediated weak localization scenario. While at high temperatures MR turns negative and its behavior is dominated by electron scattering on ferromagnetic cobalt atoms.
We synthesized pure and Co-doped (6.25 12.5 at.) ZrO$_2$ nanopowders in order to study their magnetic properties.We analyzed magnetic behavior as a function of the amount of Co and the oxygenation, which was controlled by low pressure thermal treatments. As prepared pure and Co-doped samples are diamagnetic and paramagnetic respectively. Ferromagnetism can be induced by performing low pressure thermal treatments, which becomes stronger as the dwell time of the thermal treatment is increased. This behavior can be reversed, recovering the initial diamagnetic or paramagnetic behavior, by performi…
Evolution of magnetization behaviour of cobalt film on nano patterned silicon substrate, with film thickness, has been studied. In situ magneto-optical Kerr effect measurements during film deposition allowed us to study genuine thickness dependence of magnetization behaviour, all other parameters like surface topology, deposition conditions remaining invariant. The film exhibits uniaxial magnetic anisotropy, with its magnitude decreasing with increasing film thickness. Analysis shows that anisotropy has contributions from both, i) exchange energy which is volume dependent and, ii) stray dipola…
Interfaces separating ferromagnetic (FM) layers from non-ferromagnetic layers offer unique properties due to spin-orbit coupling and symmetry breaking, yielding effects such as exchange bias, perpendicular magnetic anisotropy, spin-pumping, spin-transfer torques, conversion between charge and spin currents and vice-versa. These interfacial phenomena play crucial roles for magnetic data storage and transfer applications, which require forming FM nano-structures embedded in non-ferromagnetic matrices. Here, we investigate the possiblity of creating such nano-structures by ion-irradiation. We stu…
Using focused electron-beam-induced deposition (FEBID), we fabricate vertical, platinum-coated cobalt nanowires with a controlled three-dimensional structure. The latter is engineered to feature bends along the height: these are used as pinning sites for domain walls, the presence of which we investigate using X-ray Magnetic Circular Dichroism (XMCD) coupled to PhotoEmission Electron Microscopy (PEEM). The vertical geometry of our sample combined with the low incidence of the X-ray beam produce an extended wire shadow which we use to recover the wire's magnetic configuration. In this transmiss…
We study magnetic, transport and thermal properties of Cobalt carbide nanocomposite with a mixture of Co2C and Co3C phases in 1:1 ratio, with an average particle diameter of 40$\pm 15$ nm. We show that the behavior of the nanocomposite is completely different from that of either Co3C or Co2C. We observed that with decreasing temperature the saturation magnetization MS(T) increases, however, below 100 K, there is a steep rise. A detail analysis shows the increase in MS(T) down to 100 K is explained via the surface spin freezing model. However, below 100 K the steep increase in MS(T) is explaine…
High-density magnetic memories are key components in spintronics, quantum computing, and energy-efficient electronics. Reduced dimensionality and magnetic domain stability at the nanoscale are essential for the miniaturization of magnetic storage units. Yet, inducing magnetic order, and selectively tuning spin-orbital coupling at specific locations have remained challenging. Here we demonstrate the construction of switchable magnetic nano-islands in a nonmagnetic matrix based on cobaltite homo-structures. The magnetic and electronic states are laterally modified by epitaxial strain, which is r…
Cylindrical magnetic nanowires with large transversal magnetocrystalline anisotropy have been shown to sustain non-trivial magnetic configurations resulting from the interplay of spatial confinement, exchange, and anisotropies. Exploiting these peculiar 3D spin configurations and their solitonic inhomogeneities are prospected to improve magnetization switching in future spintronics, such as power-saving magnetic memory and logic applications. Here we employ holographic vector field electron tomography to reconstruct the remanent magnetic states in CoNi nanowires with 10 nm resolution in 3D, wi…
High coercivity induced by mechanical milling in cobalt ferrite powders
在这项工作中，我们报告的研究亚铁磁性氧化物CoFe 2 O 4的磁行为处理的机械研磨与不同的磨球。采用简单的水热法制备了钴铁氧体纳米粒子，并在500 ℃下进行了退火处理。未研磨的样品呈现约1.9kOe的磁化率、69.5emu/g的饱和磁化强度和0.42的剩磁比。球磨后，两种样品的磁化强度分别为4.2和4.1kOe，饱和磁化强度分别为67.0和71.4emu/g。这些样品的剩磁比MR/MS分别增加到0.49和0.51。为了研究这些样品的磁行为的微观结构的影响，我们使用X射线粉末衍射（XPD），透射电子显微镜（TEM），和振动样品磁强计（VSM）。通过Williamson-Hall图的XPD分析用于估计样品中由机械研磨引起的平均微晶尺寸和应变。
The nanoparticle Co3Si (P63/mmc) displays remarkable magnetism [Appl. Phys. Lett. 108, 152406 (2016)], we thus searched cobalt silicides and several phases are searched including a Cmcm with 60 meV/atom lower than that of P63/mmc. A lower-energy Co R3m (-7.03 eV/atom) is predicted, whose energy is higher than that of known P63/mmc (-7.04 eV/atom) but is lower than that of Fm3m (-7.02 eV/atom). Three small-magnetism low-energy Fe5Si3 structures are searched with energies 30 meV/atom lower than that of experimental P63/mcm. The strong lattice shape dependence of magnetocrystalline anisotropy ene…
Wereport the results of a sequence of magnetisation and magneto-optical studies on laser ablated thin films of ZnCoAlO and ZnCoO that contain a small amount of metallic cobalt. The results are compared to those expected when all the magnetization is due to isolated metallic clusters of cobalt and with an oxide sample that is almost free from metallic inclusions. Using a variety of direct magnetic measurements and also magnetic circular dichroism we find that there is ferromagnetism within both the oxide and the metallic inclusions, and furthermore that these magnetic components are exchange-co…
A detailed correlative structural, magnetic and chemical analysis of non-stoichiometric cobalt ferrite micrometric crystals was performed by x-ray magnetic circular dichroism combined with photoemission microscopy, low energy electron microscopy, and atomic force microscopy. The vector magnetization at the nanoscale is obtained from magnetic images at different x-ray incidence angles and compared with micromagnetic simulations, revealing the presence of defects which pin the magnetic domain walls. A comparison of different types of defects and the domain walls location suggests that the main s…
Transport and magnetic properties of GdBaCo_{2}O_{5+x} single crystals: A cobalt oxide with square-lattice CoO_2 planes over a wide range of electron and hole doping
