We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles (~10) at high temperatures (up to 623 K) using in situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by u0Hc=2(Kmc+Kshape)/Ms with Kmc the magnetocrystalline anisotropy constant, Kshape the shape anisotropy constant and Ms the saturation magnetization. Hc decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300 - 500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation.
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…
Effect of Decreasing Cobalt Content on the Electrochemical Properties and Structural Stability of Li_(1-x)Ni_(y)Co_(z)Al_(0.05)O_(2) Type Cathode Materials
Fe5-xGeTe2 is a van der Waals material with one of the highest reported bulk Curie temperatures, $T_C$ ~ 310K. In this study, theoretical calculations and experiments are utilized to demonstrate that the magnetic ground state is highly sensitive to local atomic arrangements and the interlayer stacking. Cobalt substitution is found to be an effective way to manipulate the magnetic properties while also increasing the ordering temperature. In particular, cobalt substitution up to 30% enhances $T_C$ and changes the magnetic anisotropy, while approximately 50% cobalt substitution yields an antifer…
The Pr$_{0.50}$Sr$_{0.5}$0CoO$_3$ perovskite exhibits unique magnetostructural properties among the rest of ferromagnetic/metallic Ln$_{0.50}$Sr$_{0.50}$CoO$_3$ compounds. The sudden orthorhombic-tetragonal (Imma $\to$ I4/mcm) structural transition produces an unusual magnetic behavior versus temperature and external magnetic fields. In particular, the symmetry change is responsible for a spontaneous spin rotation in this metallic oxide. We have studied half-doped Ln$_{0.50}$(Sr$_{1-x}$A$_x$)$_{0.50}$CoO$_3$ cobaltites varying the ionic radius rA of A-site cations (divalent cations and lanthan…
The structural and electronic properties of tin oxide nanowires: an {\it ab initio} investigation
我们对金红石型氧化锡（SnO $_{x}$）纳米线的性质进行了{ \it ab initio}研究。我们计算了几种导线尺寸和表面小平面配置的导线属性，确定平衡几何形状，结合能和电子能带结构。结果允许建立缩放律的结构特性，在纳米线周长。结果还表明，表面态控制了纳米线的大部分电子性质。纳米线表面的氧掺入钝化了表面相关的电子态，由此产生的量子特性和标度律与纳米线内部的电子完全一致。此外，线表面中的氧掺入产生了自旋向上和向下电子的不平衡浓度，导致纳米线的磁性状态。
Correlation between the structural and optical properties of spontaneously formed GaN nanowires: a quantitative evaluation of the impact of nanowire coalescence
Structural, magnetic and electric polarization properties of geometrically frustrated YBaCo4O7 and DyBaCo4O7 cobaltites
在RBaCo_4O_7（R = Ca，Y和稀土）钴酸盐家族中，只有CaBaCo_4O_7具有三维长程亚铁磁和自旋驱动的电极化的强度性质。在本研究中，我们已经研究了结构，磁性和电极化的强度性能在YBaCo 4 O 7和DyBaCo 4 O 7的这个家庭的成员，并得到的结果进行了比较与CaBaCo 4 O 7。化合物YBaCo_4O_7在5K以下表现出一系列与文献报道一致的磁性转变，并观察到团簇玻璃行为。DyBaCo_4O_7钴矿的粉末中子衍射研究表明其具有正交Pbn_（21）对称性和可果美层的短程120度磁关联特征，并在65 K以下表现出自旋玻璃行为。两种样品的介电测量结果表明，在高温下的频率分散和频率无关的行为在低温下没有介电异常。热释电电流的测量表明，在这两个样品中的宽峰约50 K，然而，仔细的分析涉及到热刺激去极化电流的峰值。这一研究表明，在kagome层的巨结构畸变和钴电荷有序是驱动长程磁有序和自旋驱动电极化的强度在这个钴族的关键因素。
Cobalt carbonate hydroxide (CCH) is a pseudocapacitive material with remarkably high capacitance and cycle stability. Previously, it was reported that CCH pseudocapacitive materials are orthorhombic in nature. Recent structural characterization has revealed that they are hexagonal in nature; however, their H positions still remain unclear. In this work, we carried out first-principles simulations to identify the H positions. Through the simulations, we could consider various fundamental deprotonation reactions inside the crystal and computationally evaluate the electromotive forces (EMF) of th…
Comprehensive investigation on the correlation of growth, structural and optical properties of GaN nanowires grown on Si(111) substrates by plasma assisted molecular beam epitaxy technique
Structural and magnetic properties of the new cobaltate series (BaSr)4-xLa2xCo4O15
报道了一类新的钴酸盐化合物（BaSr）4-xLa 2xCo 4 O 15（x = 0，0.5和1）的结构和磁性。这些化合物以六方结构结晶，其中钴离子分布在具有不同氧配位的两个不同晶体学位点之间。三个Co-O四面体和一个八面体通过共享氧原子连接形成Co 4 O 15簇，这些簇被堆积在一起形成蜂窝状网络。Sr和/或Ba原子被La部分取代允许调节Co价态混合的程度，但所有组合物仍然受到电荷随机分布的影响。磁化率与中子散射测量表明，所有研究的标本的特点是竞争铁磁和反铁磁交换相互作用，产生一个三维海森堡自旋玻璃态。中子能谱显示出一个明显的趋势，自旋动力学减慢后，增加La浓度，表明在掺杂样品中的电荷随机性减少。
Free-standing, interconnected metallic nanowire networks with density as low as 40 mg/cm^{3} have been achieved over cm-scale areas, using electrodeposition into polycarbonate membranes that have been ion-tracked at multiple angles. Networks of interconnected magnetic nanowires further provide an exciting platform to explore 3-dimensional nanomagnetism, where their structure, topology and frustration may be used as additional degrees of freedom to tailor the materials properties. New magnetization reversal mechanisms in cobalt networks are captured by the first-order reversal curve method, whi…
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…
We analyse the morphological, structural and luminescence properties of self-assembled ZnO nanowires grown by chemical vapour transport on Si(001). The examination of nanowire ensembles by scanning electron microscopy reveals that a non-negligible fraction of nanowires merge together forming coalesced aggregates during growth. We show that the coalescence degree can be unambiguously quantified by a statistical analysis of the cross-sectional shape of the nanowires. The examination of the structural properties by X-ray diffraction evidences that the nanowires crystallize in the wurtzite phase, …
High-entropy concept introduced with a promising paradigm to obtain exotic physical properties has motivated us to explore the thermoelectric properties of Sr-substituted high-entropy rare-earth cobaltates i.e., (LaNdPrSmEu)$_{1-x}$Sr$_x$CoO3 (0 \leq x \leq 0.10). The structural analysis of the samples synthesized using the standard solid-state route, confirms the orthorhombic structure with the Pbnm space group. The Seebeck coefficient and electrical resistivity decrease with rising Sr concentration as well as with an increase in temperature. The multiple A-site ions in high-entropy rare-eart…
