Absence of ferromagnetism and strong orbital coupling in carrier rich Zn/sub 1-x/In/sub x/Co/sub 0.075/O

Polycrystalline samples of Zn/sub 1-x/In/sub x/Co/sub 0.075/O (0.010/spl les/x/spl les/0.020) diluted magnetic semiconductors were prepared by the rapid oxalate decomposition technique. Phase purity is analyzed by means of X-ray diffraction technique and structures are refined by Rietveld refinement technique. Bulk conductivity of the polished pellets was measured by two-point probe technique at 295 K. Magnetic properties were analyzed with magnetic property measurement system. Samples show paramagnetic behavior and Curie-Weiss fitting at high temperature range gave effective magnetic moment of Co ions. Magnetization behavior caused by applied magnetic field was also investigated. High itinerant carrier concentration was achieved but no ferromagnetism was observed in the samples

The Electrode Properties of Mg1.9Al0.1Ni0.8Co0.1Mn0.1 Alloy by Mechanical Grinding with Ni Powders

A modified magnesium alloy of composition Mg1.9Al0.1Ni0.8Co0.1Mn0.1 was prepared by mechanical grinding with Ni powder for periods up to 120 h. The resulting structures of the Mg1.9Al0.1Ni0.8Co0.1Mn0.1 alloys were found to be amorphous. The electrodes of the modified Mg1.9Al0.1Ni0.8Co0.1Mn0.1 alloys had large discharge capacities. At a discharge current rate of 50 mA/g, the capacity was 630 mAh/g after 50 h of mechanical grinding and 510 mAh/g after 120 h of mechanical grinding

Co valence and possible spin transformation in diluted magnetic semiconductors Zn/sub 1-z/Mg/sub z/Co/sub 0.15/O and Zn/sub 1-x/Co/sub x/O

In this paper, possible spin transformation and Co valence in dilute magnetic semiconductors is studied. Polycrystalline samples of Zn/sub 1-x/Co/sub x/O (0.05/spl les/x/spl les/0.17) and Zn/sub 1-z/Mg/sub z/Co/sub 0.15/O are prepared by rapid oxalate decomposition technique. X-ray diffraction is used to determine phase purity of the samples. Co valence state 2+ is determined by X-ray absorption near edge spectroscopy (XANES) using synchrotron irradiation. Magnetic properties measured show that all samples are paramagnetic and magnetization hysteresis measurement indicated that there is no trace of ferromagnetism. From Curie-Weiss fittings at high temperature region, the effective magnetic moment (/spl mu//sub eff/) is 3.87/spl mu//sub B//Co which corresponds to that of tetrahedral Co/sup 2+/ high spin state. When fitting at T approaches 0 K, /spl mu//sub eff/ = 2.82/spl mu//sub B//Co is observed indicating a possible spin state transition to Co/sup 2+/ low spin state

Anomalous magnetization peak effect in spiral-grown Bi2Sr2CaCu2Oy crystals

Magnetic hysteresis loops were measured on spiral-grown Bi2Sr2CaCu2Oy (Bi-2212) crystals. An anomalous peak effect at a magnetic field of 1000–2000 Oe was observed both in high-Tc (86 K) and oxygen underdoped (Tc=76 K) spiral-grown crystals between 20 and 40 K. The peak effect was observed to be stronger than that induced by oxygen vacancies, defect dislocation networks reported in Bi-2212 crystals. Further, the anomalous peak almost completely disappeared after removing growth spiral patterns from the crystal surface. Edge barriers associated with the growth spirals are suggested to be responsible for the strong peak effect for the spiral-grown Bi-2212 crystals and not oxygen vacancies or screw dislocations

Characterization of LiMxFe1–xPO4 (M = Mg, Zr, Ti) Cathode Materials Prepared by the Sol-Gel Method

A series of LiMxFe12xPO4 (M 5 Mg,Zr,Ti) phosphates were synthesized via a sol-gel method. Transmission electron microscopy observations show that LiMxFe12xPO4 particles consist of nanosize crystals, ranging from 40 to 150 nm. High-resolution TEM analysis reveals that a layer of amorphous carbon was coated on the surface of the LiMxFe12xPO4 particles, which substantially increases the electronic conductivity of LiMxFe12xPO4 electrodes. The doped LiMxFe12xPO4 powders are phase pure. Near full capacity ~170 mAh/g! was achieved at the C/8 rate at room temperature for LiMxFe12xPO4 electrodes. The doped LiMxFe12xPO4 electrodes demonstrated better electrochemical performance than that of undoped LiFePO4 at high rate

An electron-losing regulation strategy for stripping modulation towards a highly reversible Zn anode

The practical application of aqueous zinc-ion batteries (AZIBs) is hindered by their low coulombic efficiency (CE) and unstable cycle life. Numerous electrolyte-additive-related studies have been performed, but most of the focus has been on the Zn plating process. In fact, practical AZIBs undergo stripping in practice rather than plating in the initial cycle, because the commonly used cathodes in the charged state do not have zinc ions, so a uniform stripping process is crucial for the cell performance of AZIBs. Here, we propose an electron-losing regulation strategy for stripping modulation by adding additives. Oxolane (OL) was chosen as the model additive to verify this assumption. It is found that OL adsorbs onto the uneven initial Zn surface and accelerates the dissolution of the Zn tips, thus providing a uniform Zn anode during the stripping process. The oxygen atoms in OL reduce the surface energy of Zn and promote the exposure of the Zn (002) surface during plating. Consequently, cells with the OL electrolyte additive maintained a long lifespan and showed superior reversibility with a high average CE. The findings of this work lead to a deep understanding of the underlying mechanism of Zn anode stripping and provide new guidance for designing electrolyte additives.</p

Magnetic and superconducting properties of Pr in La12xPrxBaCaCu3O7 system with 0.0< x <1.0

We report the results on structural aspects, magnetic, and superconducting properties of the La1-xPrxBaCaCu3O7 system. Both x-ray and neutron diffraction studies reveal that Pr substitutes isostructurally in the tetragonal LaBaCaCu3O7 (La:1113) system until the complete replacement of La by Pr. The superconducting transition temperature, Tc , determined from ac susceptibility measurements decreases, with increasing x. The relative Tc depression due to Pr in the LaBaCaCu3O7 superconductor is less in comparison to that found for La-site Pr substituted LaBa2Cu3O7 (La:123). While the critical Pr concentration (xcr) to completely suppress the superconductivity in the former is around 70 at. % of Pr at La site, the same is reported as only 30 at. % for the latter. For nonsuperconducting samples, i.e., for x=0.70 and 1.0, possible antiferromagnetic ordering with Neel temperatures, TN , of 4 and 8 K, respectively, are observed from both dc magnetic and heat capacity measurements. Interestingly in the La1-xPrx :1113 system the xcr of Pr is 0.70, and TN of Pr:1113 is 8 K, while for the La1-xPrx :123 system xCr is 0.30 and TN of Pr:123 is 17 K. The results are explained on the basis of distribution of Pr at both RE and Ba sites in the RE:1113 structure. This leads to a lower TN and a less deleterious effect of Pr on superconductivity of La:1113 compared to La:123

Structural and magnetic properties of RSr2Fe3O9 (R=La, Y, Pr, and Gd)

We have investigated the RSr2Fe3O9 (R=La, Y, Pr, and Gd) materials by several experimental techniques, including x-ray and neutron diffraction, magnetic susceptibility, and Mossbauer spectroscopy measurements. All materials studied are single phase and crystallize in the hexagonal perovskite structure. Magnetic susceptibility studies reveal that, for R=La and Pr, the Fe ions order antiferromagnetically at about TN=190 K. Short range magnetic correlations are observed up to 250 K. For R=La and Pr, 57Fe Mossbauer studies reveal two inequivalent magnetic sextets below 190 K, with the area ratio 2:1. Above TN, one singlet is observed with an isomer shift value typical to Fe4+. For R=Y and Gd, the magnetization curves do not lend themselves to easy determination of the magnetic transition due to an extra magnetic phase which exists up to 350 K. This phase is a result of deficiency of oxygen. The 57Mossbauer spectra at 300 K indicate two superimposed singlet lines, and contain a small magnetic sextet. There is no indication that the R sublattice in RSr2Fe3O9 (R=Pr and Gd) orders magnetically down to 1.5 K