Low frequency noise in asymmetric double barrier magnetic tunnel junctions with a top thin MgO layer

Low frequency noise has been investigated at room temperature for asymmetric double barrier magnetic tunnel junctions（DBMTJs）, where the coupling between the top and middle CoFeB layers is antiferromagnetic with a 0.8-nm thin top Mg O barrier of the CoFeB/MgO/CoFe/CoFeB/MgO/CoFe B DBMTJ. At enough large bias, 1/f noise dominates the voltage noise power spectra in the low frequency region, and is conventionally characterized by the Hooge parameter αmag.With increasing external field, the top and bottom ferromagnetic layers are aligned by the field, and then the middle free layer rotates from antiparallel state（antiferromagnetic coupling between top and middle ferromagnetic layers） to parallel state. In this rotation process αmag and magnetoresistance-sensitivity-product show a linear dependence, consistent with the fluctuation dissipation relation. With the magnetic field applied at different angles（θ） to the easy axis of the free layer,the linear dependence persists while the intercept of the linear fit satisfies a cos（θ） dependence, similar to that for the magnetoresistance, suggesting intrinsic relation between magnetic losses and magnetoresistance.

Effect of Quench Treatment on Fe/Mo Order and Magnetic Properties of Double Perovskite Sr_2FeMoO_6

A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2FeMo06 （SFMO）. X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9（2）% from 94.2（3）%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 #s at 300 K, and the one for the traditional sol-gel method sample is 0.946#9. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.

Magnetic and Electronic Properties of Double Perovskite Ba2SmNbO6 without Octahedral Tilting by First Principle Calculations

The structural, magnetic and electronic properties of the double perovskite Ba2SmNbO6 （for the simple cubic structure where no octahedral tilting exists anymore） are studied using the density functional theory within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction. The total energy, the spin magnetic moment, the band structure and the density of states are calculated. The optimization of the lattice constants is 8.5173 A, which is in good agreement with the experimental value 8.5180 A. The calculations reveal that Ba2SmNbO6 has a stable ferromagnetic ground state and the spin magnetic moment per molecule is 5.00μB/f.u. which comes mostly from the Sin3＋ ion only. By analysis of the band structure, the compound exhibits the direct band gap material and half-metallic ferromagnetic nature with 100% spin-up polarization, which implies potential applications of this new lanthanide compound in magneto-electronic and spintronic devices.

Endovascular Application of Magnetic Resonance Double Mismatch Technique for Acute Anterior Circulation Large Vessel Occlusion with Cerebral Infarction in an Unknown Time Window

Objective:To investigate the clinical effects of applying the magnetic resonance double mismatch technique to endovascular treatment of acute anterior circulation,large vessel occlusion with cerebral infarction in an unknown time window.Methods:The research work was carried out in our hospital,the work was carried out from November 2018 to November 2019,the patients with acute anterior circulation large vessel occlusion with cerebral infarction who were treated in our hospital during this period,100 patients,50 patients with an unknown time window and 50 patients with definite time window were selected,and they were named as the experimental and control groups,given different examination methods,were given to investigate the clinical treatment effect.Results:Patients’data on HIHSS score before treatment,the incidence of intracranial hemorrhage and rate of Mrs≤2 rating after 90 days of treatment were not significantly different(P>0.05),which was not meaningful.The differences in data between the two groups concerning HIHSS scores were relatively significant before,and after treatment(P<0.05).Conclusion:The magnetic resonance double mismatch technique will be applied in the endovascular treatment of acute anterior circulation large vessel occlusion with cerebral infarction of unknown time window.

Interpretation method of nuclear magnetic resonance dual-TW logging in oil-wet tight sandstone reservoirs

Fluid typing from nuclear magnetic resonance(NMR)logging in oil-wet tight sandstone reservoirs is proving to be diffi cult;thus,research into the NMR logging response mechanism and analysis methods is critical.The NMR response mechanism and theoretical method were investigated based on the oil-water distribution in the pores under oil-wet conditions.The data processing method is studied based on NMR dual-TW activation principle,and the equations of macroscopic magnetization vector,fl uid volume,and relaxation parameters are derived,which is a nonlinear inversion problem.The simulated annealing algorithm is used,and the fl uid relaxation parameters,oil volume,and water volume of the fl ushing zone are calculated.An ideal reservoir model is set up,and simulation results indicate that the above-mentioned NMR relaxation theory and algorithms are valid.A case study is conducted in Huanjiang Oilfi eld in the Ordos Basin,China.The calculated oil saturation of the fl ushing zone is consistent with the oil saturation calculated using the Archie formula,and the test results indicated that the new method is applicable.Moreover,the fl uid-typing cross-plot combined with oil test data is constructed on the basis of the saturation of the fl ushing zone,improving the accuracy of fl uid identifi cation.

Synthesis pretreatment and characterization of a magnetic layered double hydroxides fluorescent probe

Using magnetic layered double hydroxide （MLDH） as carrier of fluorescein （FLU）, a fluorescent composite of MLDH-FLU was prepared via intercalation reaction of ion change. The crystal properties of MLDH-FLU were investigated through XRD, IR, TEM and TG-DSC characterization. It is shown that the crystal type of MLDH-FLU composite matched well with R-hexagonal crystal system of MLDH, with crystal cell parameters of a, c and channel height h equal to 0.3199, 2.411 and 0.3267 nm respectively. The superabundant pigment adsorbed outside the composite should be cleared before interference with cells, but excessive wash would decrease stability and cause crystal phase transformation of MLDH.

Double Emulsion Droplets as Microreactors for Synthesis of Magnetic Macroporous Polymer Beads

An easy method is presented to fabricate monodisperse magnetic macroporous polymer beads（MMPBs）. Waterin-oil high internal phase emulsion（HIPE） is prepared by emulsifying aqueous iron ions solution in an oil phase containing monomers. The HIPE is introduced into a simple microfluidic device to fabricate monodisperse（water-in-oil）-in-water double emulsion droplets. The droplets serve as microreactors to synthesize Fe3O4 nanoparticles and are on-line polymerized to form MMPBs. The prepared MMPBs display uniform size, interconnected porous structure, superparamagnetic behavior and uniform distribution of Fe3O4 in polymer matrix. The MMPBs are characterized by scanning electron microscopy（SEM）, Fourier transform infrared spectroscopy（FTIR）, X-ray diffraction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometry（VSM）. We believe that this method is a universal technique in preparing macroporous nanocomposite beads.

Controllable magnetic properties of cobalt ferrite particles derived from layered double hydroxide precursors

Cobalt ferrite CoxNi1-xFe2O4 （x = 0, 0.5, 1 ） particles with controllable magnetic properties have been prepared by calcination of co-substituted NiFe^2＋Fe^3＋ -layered double hydroxide （NiFe^2＋Fe^3＋-LDH） precursors prepared via a scalable method involving separate nucleation and aging steps （SNAS）. Their structural and magnetic characteristics were investigated by powder X-ray diffraction （XRD）, scanning electron microscopy （SEM） and vibrating sample magnetometry （VSM）. Measurements of magnetic properties show that the saturation magnetization （Ms） and coercivity （He） of the calcined products increased with increasing cobalt content. The LDH precursor-based product obtained by calcination of a mixture of CoFe^2＋Fe3^＋-LDH and NiFe^2＋Fe^3＋ -LDH powders with a Co/Ni molar ratio of 1：1, exhibits a moderate value of Ms and an increased value of He compared to the corresponding values for an Ni0.5Co0.5Fe2O4 material prepared by calcination of a Co0.5Ni0.5Fe^2＋Fe^3＋-LDH precursor, and a physical mixture of CoFe2O4 and NiFe2O4 with a Co/Ni molar ratio of 1 ： 1. These results may provide a way to regulate magnetic anisotropy of ferrite spinels by varying the composition of the LDH precursors.

Relationship between controllable preparation and microstructure of NdFeB sintered magnets

The double hard magnetic phase magnets with nominal compositions of Nd30–xDyxFe69B1（x=2, and 4）（wt.%） were prepared. The magnetic properties of the magnets were measured with a NIM-2000H hysteresigraph. The crystalline structures of the magnets were identified by X-ray diffraction（XRD）. The Rietveld refinement was carried out using the FULLPROF software. The scanning electron microscopy（SEM） and transmission electron microscopy（TEM） analyses were carried out in order to investigate the microstructure of the magnets. It showed that the magnets consisted mainly of Nd2Fe14 B phase, and some Nd-rich phase. Two types of matrix-phase grains in dark grey and light grey were found in the magnets with x=2 and 4. The Dy content was obviously different in the two types of grains, which proved that the double hard magnetic phases（Dy-rich and Dy-lean phases） coexisted in the magnet. It revealed that the Nd-rich phases in junction regions had fcc structure, with the unit cell parameter of about 0.52–0.56 nm. The weak superlattice spots were found in the SAD patterns of the junction Nd-rich phases with large scale. The double hard magnetic phase structure seemed to improve the magnetic properties of NdFeB magnets with high coercivity, while decrease the consumption of Dy element, compared with the single alloy magnet.