Total ionizing radiation-induced read bit-errors in toggle magnetoresistive random-access memory devices

The 1-Mb and 4-Mb commercial toggle magnetoresistive random-access memories（MRAMs） with 0.13 μm and 0.18-μm complementary metal–oxide–semiconductor（CMOS） process respectively and different magnetic tunneling junctions（MTJs） are irradiated with a Cobalt-60 gamma source. The electrical functions of devices during the irradiation and the room temperature annealing behavior are measured. Electrical failures are observed until the dose accumulates to 120-krad（Si） in 4-Mb MRAM while the 1-Mb MRAM keeps normal. Thus, the 0.13-μm process circuit exhibits better radiation tolerance than the 0.18-μm process circuit. However, a small quantity of read bit-errors randomly occurs only in 1-Mb MRAM during the irradiation while their electrical function is normal. It indicates that the store states of MTJ may be influenced by gamma radiation, although the electrical transport and magnetic properties are inherently immune to the radiation. We propose that the magnetic Compton scattering in the interaction of gamma ray with magnetic free layer may be the origin of the read bit-errors. Our results are useful for MRAM toward space application.

Effects of substrate temperature and annealing on the anisotropic magnetoresistive property of NiFe films

Ni_(83)Fe_(17) films with a thickness of about 100 nm were deposited onthermal oxidized silicon substrates at ambient temperature, 240, 350, and 410℃ by DC magnetronsputtering. The deposition rate was about 0.11 nm/s. The as-deposited films were annealed at 450,550, and 650℃, respectively, in a vacuum lower than 3 x 10~3 Pa for 1 h. The Ni_(83)Fe_(17) filmsmainly grow with a crystalline orientation of [111] in the direction of the film growth. With theannealing temperature increasing, the [111] orientation enhances. For films deposited at all fourdifferent temperatures, the significant improvement on anisotropic magnetoresistance occurs at theannealing temperature higher than 550℃. But for films deposited at ambient temperatures and 240 ℃,the anisotropic magnetoresistance can only rise to about 1% after 650 ℃ annealing. For filmsdeposited at 350℃ and 410℃, the anisotropic magnetoresistance rises to about 3.8% after 650℃annealing. The atomic force microscopy (AFM) observation shows a significant increase in grain sizeof the film deposited at 350℃ after 650℃ annealing. The decrease in resistivity and the increasein anisotropic magnetoresistance are caused by the decrease in point defects, the increase in grainsize, and the improvement in lattice structure integrity of the films.

The magnetoresistive effect induced by stress in spin-valve structures

Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic （FM） monolayer and an FM/antiferromagnetic （AFM） bilayer under a stress field, respectively. It then investigates the magnetoresistance （MR） of the spin-valve structure, which is built by an FM rnonolayer and an FM/AFM bilayer, and its dependence upon the applied stress field. The results show that under the stress field, the magnetization properties of the FM monolayer is obviously different from that of the FM/AFM bilayer, since the coupled AFM layer can obviously block the magnetization of the FM layer. This phenomenon makes the MR of the spin-valve structure become obvious. In detail, there are two behaviors for the MR of the spin-valve structure dependence upon the stress field distinguished by the coupling （FM coupling or AFM coupling） between the FM layer and the FM/AFM bilayer. Either behavior of the MR of the spin-valve structure depends on the stress field including its value and orientation. Based on these investigations, a perfect mechanical sensor at the nano-scale is suggested to be devised experimentally.

Magnetoresistive behavior and magnetization reversal of NiFe/Cu/CoFe/IrMn spin valve GMRs in nanoscale

The magnetoresistance behavior and the magnetization reversal mode of NiFe/Cu/CoFe/IrMn spin valve giant magnetoresistance （SV-GMR） in nanoscale were investigated experimentally and theoretically by nanosized magnetic simulation methods. Based on the Landau-Lifshitz-Gilbert equation, a model with a special gridding was proposed to calculate the giant magnetoresistance ratio （MR） and investigate the magnetization reversal mode. The relationship between MR and the external magnetic field was obtained and analyzed. Studies into the variation of the magnetization distribution reveal that the magnetization reversal mode, that is, the jump variation mode for NiFe/Cu/CoFe/IrMn, depends greatly on the antiferromagnetic coupling behavior between the pinned layer and the antiferromagnetic layer. It is also found that the switching field is almost linear with the exchange coefficient.

Magnetoresistive sensors with hybrid Co/insulator/ZnO:Co junctions

Magnetic tunnel junctions （MTJs）, as the seminal spintronic devices, are expected for applications in magne- toresistive sensors due to their large magnetoresistance （MR） and high field sensitivity. Two hybrid Co/insulator/ZnO：Co junctions were fabricated with two different barriers to investigate the magneto-transport properties. Experimental results indicate that, both Co/MgO/ZnO：Co and Co/ZnO/ZnO：Co junctions show the positive and nearly linear MR, and their tunnel magnetoresistances （TMR） are 21.8% and 13.6%, respectively, when the current is applied perpendicular to the film plane under the magnetic field of 2 T at 4 K. The nonlinearity of MR is less than 1% within the magnetic field （H） of 1 kOe 〈 H 〈 12 kOe at low temperature, making them attractive as magnetoresistive sensors. The higher MR of Co/MgO/ZnO：Co junctions is due to the superior spin filtering effect and larger effective barrier height of the MgO barrier. This linear MR characteristic of Co/insulator/ZnO：Co structures shows a promising future on the applications of diluted magnetic semiconductors in magnetoresistive sensors.

Low temperature magnetoresistive effects and coulomb blockade in La_0.7Ca_0.3MnO₃nanoparticles synthesis by auto-Ignition method

Electrical transport properties of the La0.7Ca0.3MnO3nanoparticles have been inves-tigated in the temperature range 300 to 9 K as a function of magnetic field. Samples were pre-pared by auto-ignition method. In low tempera-ture regime from 40 to 9 K, an increase in the resistivity has been observed. This effect is found to decrease as magnetic field is increased. It is assumed that these effects are due to the magnetic contacts between the nanoparticles.

Construction and Validation of Simple Magnetic Nanoparticle Detector Based on Giant Magnetoresistive Effect

The finding of giant magnetoresistive（GMR） effect develops a new field for the sensing application with magnetic nanoparticles（MNPs） labeling. A convenient GMR sensor was built with a permanent magnet to excite the MNPs in this work. The sensing element contained a Wheatstone bridge with the GMR material as one of its branches. The magnetic field from MNPs unbalanced the Wheatstone bridge. After being amplified, the output signals were recorded. The construction and optimization of the magnetoresistive sensing platform were discussed in detail. The detection of three kinds of MNPs validated the performance of the proposed GMR sensor. The sensor showed a fast response to the addition or removal of MNPs. Because of its simplicity, this kind of GMR sensor can be developed in a routine laboratory. The finding of this new GMR sensor will promote the development of the method of probing biomoleeules and the study on the biomolecular interaction after being labeled magnetically.

Anisotropic spin transport and photoresponse characteristics detected by tip movement in magnetic single-molecule junction

Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions.Here,using the first-principles method,we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites.The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry.The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%.Moreover,as the Ni tip electrode moves,the tunneling magnetoresistance of upright molecular junctions can be increased to 70%.The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation,where the molecule in upright molecular junctions yields higher spin polarization.Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.

Pressure-induced magnetic phase and structural transition in SmSb_(2)

Motivated by the recent discovery of unconventional superconductivity around a magnetic quantum critical point in pressurized CeSb_(2),here we present a high-pressure study of an isostructural antiferromagnetic(AFM) SmSb_(2) through electrical transport and synchrotron x-ray diffraction measurements.At P_C~2.5 GPa,we found a pressure-induced magnetic phase transition accompanied by a Cmca→P4/nmm structural phase transition.In the pristine AFM phase below P_C,the AFM transition temperature of SmSb_(2) is insensitive to pressure;in the emergent magnetic phase above P_C,however,the magnetic critical temperature increases rapidly with increasing pressure.In addition,at ambient pressure,the magnetoresistivity(MR) of SmSb_(2) increases suddenly upon cooling below the AFM transition temperature and presents linear nonsaturating behavior under high field at 2 K.With increasing pressure above P_C,the MR behavior remains similar to that observed at ambient pressure,both in terms of temperature-and field-dependent MR.This leads us to argue an AFM-like state for SmSb_(2) above P_C.Within the investigated pressure of up to 45.3 GPa and the temperature of down to 1.8 K,we found no signature of superconductivity in SmSb_(2).

Magnetic Switching Dynamics and Tunnel Magnetoresistance Effect Based on Spin-Splitting Noncollinear Antiferromagnet Mn_(3)Pt

In comparison to ferromagnets,antiferromagnets are believed to have superior advantages for applications in next-generation magnetic storage devices,including fast spin dynamics,vanishing stray fields and robust against external magnetic field,etc.However,unlike ferromagnetic orders,which could be detected through tunneling magnetoresistance effect in magnetic tunnel junctions,the antiferromagnetic order(i.e.,Néel vector)cannot be effectively detected by the similar mechanism due to the spin degeneracy of conventional antiferromagnets.Recently discovered spin-splitting noncollinear antiferromagnets,such as Mn_(3)Pt with momentum-dependent spin polarization due to their special magnetic space group,make it possible to achieve remarkable tunneling magnetoresistance effects in noncollinear antiferromagnetic tunnel junctions.Through first-principles calculations,we demonstrate that the tunneling magnetoresistance ratio can reach more than 800% in Mn_(3)Pt/perovskite oxides/Mn_(3)Pt antiferromagnetic tunnel junctions.We also reveal the switching dynamics of Mn_(3)Pt thin film under magnetic fields using atomistic spin dynamic simulation.Our study provides a reliable method for detecting Néel vector of noncollinear antiferromagnets through the tunnel magnetoresistance effect and may pave its way for potential applications in antiferromagnetic memory devices.

Linear magnetoresistance and structural distortion in layered SrCu_(4-x)P_(2) single crystals

We report a systematic study on layered metal SrCu_(4-x)P_(2) single crystals via transport, magnetization, thermodynamic measurements and structural characterization. We find that the crystals show large linear magnetoresistance without any sign of saturation with a magnetic field up to 30T. We also observe a phase transition with significant anomalies in resistivity and heat capacity at T_(p)~140 K. Thermal expansion measurement reveals a subtle lattice parameter variation near Tp, i.e.,?L_(c)/L_(c)~0.062%. The structural characterization confines that there is no structure transition below and above T_(p). All these results suggest that the nonmagnetic transition of SrCu_(4-x)P_(2) could be associated with structural distortion.

Negative magnetoresistance in the antiferromagnetic semimetal V_(1/3)TaS_(2)

Intercalated transition metal dichalcogenides(TMDCs)attract much attention due to their rich properties and potential applications.In this article,we grew successfully high-quality V_(1/3)TaS_(2) crystals by a vapor transport method.We measured the magnetization,longitudinal resistivityρxx(T,H),Hall resistivityρxy(T,H),as well as performed calculations of the electronic band structure.It was found that V_(1/3)TaS_(2) is an A-type antiferromagnet with the Neel temperature T_(N)=6.20 K,and exhibits a negative magnetoresistance(MR)near T_(N).Both band structure calculations and Hall resistivity measurements demonstrated it is a magnetic semimetal.

Unconventional room-temperature negative magnetoresistance effect in Au/n-Ge:Sb/Au devices

Non-magnetic semiconductor materials and their devices have attracted wide attention since they are usually prone to exhibit large positive magnetoresistance(MR)effect in a low static magnetic field environment at room temperature.However,how to obtain a large room-temperature negative MR effect in them remains to be studied.In this paper,by designing an Au/n-Ge:Sb/Au device with metal electrodes located on identical side,we observe an obvious room-temperature negative MR effect in a specific 50 T pulsed high magnetic field direction environment,but not in a static low magnetic field environment.Through the analysis of the experimental measurement of the Hall effect results and bipolar transport theory,we propose that this unconventional negative MR effect is mainly related to the charge accumulation on the surface of the device under the modulation of the stronger Lorentz force provided by the pulsed high magnetic field.This theoretical analytical model is further confirmed by regulating the geometry size of the device.Our work sheds light on the development of novel magnetic sensing,magnetic logic and other devices based on non-magnetic semiconductors operating in pulsed high magnetic field environment.

High efficiency giant magnetoresistive device based on two-dimensional MXene(Mn_(2)NO_(2))

Due to the unique electronic structure of half-metals,characterized by the conductivity of majority-spin and the band gap of minority-spin,these materials have emerged as suitable alternatives for the design of efficient giant magnetoresistive(GMR)devices.Based on the first-principles calculations,an excellent GMR device has been designed by using two-dimensional(2D)half-metal Mn_(2)NO_(2).The results show that Mn_(2)NO_(2)has sandwiched between the Au/nMn_(2)NO_(2)(n=1,2,3)/Au heterojunction and maintains its half-metallic properties.Due to the half-metallic characteristics of Mn_(2)NO_(2),the total current of the monolayer device can reach up to 1500 nA in the ferromagnetic state.At low voltage,the maximum GMR is observed to be 1.15×1031%.Further,by increasing the number of layers,the ultra-high GMR at low voltage is still maintained.The developed device is a spintronic device exhibiting the highest magnetoresistive ratio reported theoretically so far.Simultaneously,a significant negative differential resistance(NDR)effect is also observed in the heterojunction.Owing to its excellent half-metallic properties and 2D structure,Mn_(2)NO_(2)is an ideal energy-saving GMR material.

Magnetoresistive properties of Ni-doped La_(0.7)Sr_(0.3)MnO_3 manganites

Lao.7Sr0.3Mnl_xNixO3 （x = 0, 0.025, 0.050 and 0.075） ceramics were prepared by the conventional solid-state reaction method. The partial substitution of Mn by Ni2＋ leads to a decrease in cell volume as well as a structural transition from the rhombohedral to the orthorhombic structure. Ni2＋ doping increases the electrical resistivity, decreases the semiconductor-metal transition temperature （Tms） and relatively enhances the room temperature magnetoresistance （MR）, especially in x = 0.025 and around Tins. With respect to conduction mechanism, the small polaron hopping （SPH） and the variable range hopping （VRH） models were used to ex- amine conduction in the semiconducting region.

Colossal negative magnetoresistance in spin glass Na(Zn,Mn)Sb

We report the study of magnetic and transport properties of polycrystalline and single crystal Na(Zn,Mn)Sb,a new member of“111”type of diluted magnetic materials.The material crystallizes into Cu2Sb-type structure which is isostructural to“111”type Fe-based superconductors.With suitable carrier and spin doping,the Na(Zn,Mn)Sb establishes spin-glass ordering with freezing temperature(Tf)below 15 K.Despite lack of long-range ferromagnetic ordering,Na(Zn,Mn)Sb single crystal still shows sizeable anomalous Hall effect below Tf.Carrier concentration determined by Hall effect measurements is over 1019 cm-3.More significantly,we observe colossal negative magnetoresistance(MR≡[ρ(H)−ρ(0)]/ρ(0))of-94%in the single crystal sample.

Spin injection into heavily-doped n-GaN via Schottky barrier

Spin injection and detection in bulk GaN were investigated by performing magnetotransport measurements at low temperatures.A non-local four-terminal lateral spin valve device was fabricated with Co/GaN Schottky contacts.The spin injection efficiency of 21%was achieved at 1.7 K.It was confirmed that the thin Schottky barrier formed between the heavily ndoped GaN and Co was conducive to the direct spin tunneling,by reducing the spin scattering relaxation through the interface states.

Negative magnetoresistance in Dirac semimetal Cd_(3)As_(2)with in-plane magnetic field perpendicular to current

Topological insulators and semimetals have exotic surface and bulk states with massless Dirac or Weyl fermions,demonstrating microscopic transport phenomenon based on relativistic theory.Chiral anomaly induced negative magnetoresistance(negative MR)under parallel magnetic field and current has been used as a probable evidence ofWeyl fermions in recent years.Here we report a novel negative MR result with mutually perpendicular in-plane magnetic field and current in Cd_(3)As_(2)nanowires.The negative MR has a considerable value of-16%around 1.5 K and could persist to room temperature of 300 K with value of-1%.The gate tuning and angle dependence of the negative MR demonstrate the mechanism of the observed negative MR is different from the chiral anomaly.Percolating current paths induced by charge puddles and disorder might be involved to produce such considerable negative MR.Our results indicate the negative MR effect in topological semimetals involves synergistic effects of many mechanisms besides chiral anomaly.

Abnormal magnetoresistance effect in the Nb/Si superconductor–semiconductor heterojunction

Ultrathin superconducting Nb films of about 8 nm thick have been deposited on heavily doped Si substrates through DC magnetron sputtering and then the high-quality Nb/Si superconductor–semiconductor heterojunctions have been fabricated by electron beam lithography and reactive ion etching.An abnormal magnetoresistance effect,which manifests itself as a zero field resistance peak under a magnetic field applied perpendicular to the interface,has been distinctly observed when the Nb film is in the superconductiing state.By considering the heterojunction interface being equivalent to the structure of superconductor–barrier layer–superconductor configuration,we could generally understand this unusual effect based on the Andreev reflection mechanism.Our results can be of help for the future development on compatibility and scalability of the silicon-based nanoscale superconducting devices for integrated circuits and superconducting quantum electronics.

Nonmonotonic anomalous Hall effect and anisotropic magnetoresistance in SrRuO_(3)/PbZr_(0.52)Ti_(0.48)O_(3)heterostructures

We fabricate SrRuO_(3)/PbZr_(0.52)Ti_(0.48)O_(3)heterostructures each with an in-plane tensile-strained SrRuO_(3)layer and investigate the effect of an applied electric field on anomalous Hall effect.The four-fold symmetry of anisotropic magnetoresistance and the nonmonotonic variation of anomalous Hall resistivity are observed.By applying positive electric field or negative electric field,the intersecting hump-like feature is suppressed or enhanced,respectively.The sign and magnitude of the anomalous Hall conductivity can be effectively controlled with an electric field under a high magnetic field.The electric-field-modulated anomalous Hall effect is associated with the magnetization rotation in SrRuO_(3).The experimental results are helpful in modulating the magnetization rotation in spintronic devices based on SrRuO_(3)heterostructures.