Effect of native defects and Co doping on ferromagnetism in HfO2: first-principles calculations.

First-principles calculations of undoped HfO(2) and cobalt-doped HfO(2) have been carried out to study the magnetic properties of the dielectric material. In contrast to previous reports, it was found that the native defects in HfO(2) could not induce strong ferromagnetism. However, the cobalt substituting hafnium is the most stable defect under oxidation condition, and the ferromagnetic (FM) coupling between the cobalt substitutions is favorable in various configurations. We found that the FM coupling is mediated by the threefold-coordinated oxygen atoms in monoclinic HfO(2) and could be further enhanced in electron-rich condition.

3,3'-(2-Oxocyclo-pentane-1,3-di-yl)dipropane-nitrile.

The complete mol-ecule of the title compound, C(11)H(14)N(2)O, is generated by crystallographic twofold symmetry, with the C=O group lying on the rotation axis. In the crystal structure, weak C-H⋯N inter-actions form zigzag chains of mol-ecules.

N-(2-Formamido-eth-yl)formamide.

The complete molecule of the title compound, C(4)H(8)N(2)O(2), is generated by a crystallographic inversion center. The occurence of N-H⋯O hydrogen bonds results in the formation of a two-dimensional infinite network parallel to the (010) plane. In this plane, the hydrogen bonds define graph-set motif R(4) (4)(22) in a centrosymmetric array by the association of four mol-ecules.

Bis(4-pyridylmeth-yl) hexa-nedioate.

The asymmetric unit of the title compound, C(18)H(20)N(2)O(4), contains one half-mol-ecule. The mol-ecule lies on an inversion centre and is roughly planar, the chains between the two pyridine rings being only slightly twisted, with torsion angles ranging from 170.9 (1) to 177.2 (1)°. Weak C-H⋯O hydrogen bonds result in the formation of a three-dimensional network.

4-Hydroxy-2,2,6,6-tetra-methyl-piperidinium trifluoro-acetate.

The title compound, C(9)H(20)NO(+)·C(2)F(3)O(2) (-), is an important inter-mediate in the synthesis of hindered light stabilizers. The piperidinium ring adopts a chair conformation with the hydroxyl group in an equatorial position. The crystal packing is stabilized by O-H⋯O and N-H⋯O hydrogen bonds. The CF(3) group is disordered over two positions with almost equal site occupancy factors.

Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions.

Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

Electrical control of memristance and magnetoresistance in oxide magnetic tunnel junctions.

Electric-field control of magnetic and transport properties of magnetic tunnel junctions has promising applications in spintronics. Here, we experimentally demonstrate a reversible electrical manipulation of memristance, magnetoresistance, and exchange bias in Co/CoO-ZnO/Co magnetic tunnel junctions, which enables the realization of four nonvolatile resistance states. Moreover, greatly enhanced tunneling magnetoresistance of 68% was observed due to the enhanced spin polarization of the bottom Co/CoO interface. The ab initio calculations further indicate that the spin polarization of the Co/CoO interface is as high as 73% near the Fermi level and plenty of oxygen vacancies can induce metal-insulator transition of the CoO(1-v) layer. Thus, the electrical manipulation mechanism on the memristance, magnetoresistance and exchange bias can be attributed to the electric-field-driven migration of oxygen ions/vacancies between very thin CoO and ZnO layers.

Spin memristive magnetic tunnel junctions with CoO-ZnO nano composite barrier.

The spin memristive devices combining memristance and tunneling magnetoresistance have promising applications in multibit nonvolatile data storage and artificial neuronal computing. However, it is a great challenge for simultaneous realization of large memristance and magnetoresistance in one nanoscale junction, because it is very hard to find a proper spacer layer which not only serves as good insulating layer for tunneling magnetoresistance but also easily switches between high and low resistance states under electrical field. Here we firstly propose to use nanon composite barrier layers of CoO-ZnO to fabricate the spin memristive Co/CoO-ZnO/Co magnetic tunnel junctions. The bipolar resistance switching ratio is high up to 90, and the TMR ratio of the high resistance state gets to 8% at room temperature, which leads to three resistance states. The bipolar resistance switching is explained by the metal-insulator transition of CoO(1-v) layer due to the migration of oxygen ions between CoO(1-v) and ZnO(1-v).