Magnetoresistance Values Research Articles

Particles-Matrix Bond in ZnCoO:H and ZnCoAlO:H Films: Issues of Magnetism and Spin Injection.

ZnCoO:H and ZnCoAlO:H films were synthesized by radio frequency magnetron sputtering in a (1 - x)Ar + xH2 mixed atmosphere with x = 0.2-0.5. The films contain different amounts of metallic Co particles (from 7.6% and higher) ~4-7 nm in size. The magnetic and magneto-optical (MO) behavior of the films was analyzed in combination with their structural data. The samples exhibit high values of magnetization (up to 377 emu/cm3) and MO response at room temperature. Two situations are considered: (1) the film magnetism is associated only with isolated metal particles and (2) magnetism is present both in the oxide matrix and in metal inclusions. It has been established that the formation mechanism of the magnetic structure of ZnO:Co2+ is due to the spin-polarized conduction electrons of metal particles and zinc vacancies. It was also found that in the presence of two magnetic components in the films, these components are exchange-coupled. In this case, the exchange coupling generates a high spin polarization of the films. The spin-dependent transport properties of the samples have been studied. A high value of the negative magnetoresistance of the films at room temperature (~4%) was found. This behavior was explained in terms of the giant magnetoresistance model. Thus, the ZnCoO:H and ZnCoAlO:H films with high spin polarization can be considered as sources of spin injection.

Magnetotransport property of oxygen-annealed Fe1+y Te thin films

Fe-based superconductors are one of the current research focuses. FeTe is unique in the series of FeSe1−x Te x , since it is nonsuperconducting near the FeTe side in the phase diagram in contrast to the presence of superconductivity in other region. However, FeTe thin films become superconducting after oxygen annealing and the mechanism remains elusive. Here, we report the temperature dependences of resistivity, Hall effect and magnetoresistance (MR) of a series of FeTe thin films with different amounts of excess Fe and oxygen. These properties show dramatic changes with excess Fe and oxygen incorporation. We found the Hall coefficients are positive for the oxygen-annealed samples, in contrast to the transition from positive to negative below 50 K for the vacuum-annealed samples. For all samples, both the resistivity and Hall coefficient show a dramatic drop, respectively, at around 50 K–75 K, implying coexistence of superconductivity and antiferromagnetic order for the oxygen-annealed samples. The vacuum-annealed samples show both positive and negative values of MR depending on temperature, while negative MR dominates for the oxygen-annealed samples. We also found that oxygen annealing reduces the excess Fe in FeTe, which has been neglected before. The results are discussed in terms of several contributions, and a comparison is made between the oxygen-annealed FeTe thin films and FeSe1−x Te x . This work is helpful for shedding light on the understanding of oxygen-annealed FeTe thin films.

Variation of Electrical Resistivity During Magnetic Field-Induced Martensitic Transformation in Vanadium added NiMnSnB alloys

In this study, the structural and electrical properties of Ni49-xVxMn37Sn12B2 (x = 0, 1, 2, and 3) ferromagnetic shape memory alloys were investigated. According to XRD analyzes at room temperature, the x=0 sample was in the martensite phase, the x=1 and 2 samples were in the mixture phase, and the x=3 sample was in the austenite phase. The resistivity analyses depend on temperature showed that all samples exhibited martensitic transformation and the phase transformation temperature decreased with V doping. Magnetoresistance (MR) values were calculated using ρ-T curves performed under 0 T and 1 T magnetic fields. The observed negative MR is consistent with Kataoka's s-d model. As-Af interval was determined and M-H measurements were made at constant temperatures determined in this interval. The results were attributed to the magnetic field-induced phase transformation (MFIPT). In order to examine the effects of MFIPT on the electrical resistivity, the resistivity depend on magnetic field was measured using the same thermal process. The overlapping of the curves in the high magnetic field revealed that the resistivity decreased due to the MFIPT as well as the MR.

Electron conduction mechanisms in magnetic tunnel junctions fabricated using amorphous Si-Zn-Sn-O as a low-resistive semiconducting barrier

CoFeB/ Si-Zn-Sn-O /CoFeB magnetic tunnel junctions (MTJs) have been fabricated using amorphous Si-Zn-Sn-O as a low-resistive semiconducting barrier. In the low bias voltage range (up to ∼0.2 V), direct tunneling is found to be the dominant transport mechanism in MTJs. Tunneling conduction is further verified by simulation of tunnel current density and differential conductance using Simmon’s and Brinkmann model, respectively. Simulated results provided valuable insights into the barrier properties, including interfacial barrier height, thickness, and barrier asymmetry. Above the direct tunneling regime, electron transport in MTJs is governed by Pool Frenkel emission, which possibly arises due to the presence of high-density localized tail states below the conduction band of amorphous Si-Zn-Sn-O. Tunnelling magnetoresistance value of MTJs is found to be very low, which is attributed to the presence of various inelastic conduction channels. The results of this study might be useful to explore the potential of amorphous Si-Zn-Sn-O for fabricating low-resistive MTJ based spintronic devices.

Structure redetermination, transport and thermal properties of the YNi3Al9 compound

Single crystals of completely ordered variant of the YNi3Al9 compound were grown by self-flux method with excess of aluminum. The crystal structure of the title compound was redetermined from single crystal X-ray diffraction data. The structure adopts ErNi3Al9 type, space group R32, parameters of the unit cell a ​= ​7.2838(2) Å, c ​= ​27.4004(8) Å. The growth of relatively large single crystals of the YNi3Al9 compound, having completely ordered structure, indicates possible existence of region on phase diagram, where the title compound is in equilibrium with liquid. Comparison with the results in the literature on the investigations of the same and related compounds shows trend towards formation of more ordered structures in flux grown samples and more disordered ones in arc melted samples.Physical properties of the title compound - electrical resistivity, magnetoresistance and heat capacity - were measured for the first time. It shows metallic-like behavior with very high values of magnetoresistance up to 420% at low temperatures without presence of magnetic elements. Therefore electronic structure calculations were carried out. The phonon heat capacity reveals major Debye and minor Einstein contributions at the intermediate temperatures, and total heat capacity approaches Dulong-Petit limit at high temperatures. The calculated Debye temperature from the whole temperature range θD ​= ​480(6) K is typical for aluminium-rich compounds. Corresponding Einstein temperature is θE ​= ​198(8) K. The estimations of electron-phonon coupling constant λ ​= ​0.092 show very weak coupling and absence of superconducting transition.

Stacking Order, Perfect Spin Polarization, and Giant Magnetoresistance in Zigzag Graphene/ h - BN Heterobilayer Nanoribbons

In a van der Waals heterostructure of two-dimensional materials, electronic properties are tunable by means of stacking orders. Here, we study the spin-dependent quantum transport in the bilayer of ferromagnetic zigzag-edged graphene/hexagonal-$\mathrm{BN}$ nanoribbons (ZGr-BNNRs) using density-functional theory combined with the Keldysh nonequilibrium Green's-function method. We reveal a strong odd-even effect of transport across the ZGr-BNNRs and a giant magnetoresistance value observed only in even-width ZGr-BNNRs. More interestingly, this value can be optimized by engineering stacking orders, yielding the perfect spin polarization efficiency of 100% and the magnetoresistance value of over ${10}^{4}$ in even-width ZGr-BNNRs. Our results provide a route to design and fabricate high-performance spin filters and magnetic storage devices.

Enhancement of magnetoresistance with the variation of particle size in La0.68−xYxCa0.32MnO3, x = 0.0, 0.4, 0.5, 0.6

Huge magnetoresistance (MR) has been achieved in La0.68Ca0.32MnO3, by optimal substitution. To explore the origin of this giant enhancement of MR, we have carried out magnetic and magneto transport measurements of La0.68−xYxCa0.32MnO3, x = 0.0, 0.4, 0.5, 0.6 compounds in detail. Our analysis indicates that the disorder introduced by yttrium substitution plays the crucial role in the magneto resistive properties in this series. A large MR has been observed in optimally doped x = 0.5. In this compound, an MR value as high as 1.5 × 107% at a temperature of 50 K has been achieved for an external magnetic field of 90 kOe. The extraordinarily enhanced and large MR value has been described using a phenomenological model of percolation via ferromagnetic clusters. At the specific temperature sizes of these s compounds increases and MR% is likewise increased. For x = 0.6,not enough to create the percolation path.

Substrate temperature dependence of microstructure and magnetoresistance field sensitivity of Co–ZnO non-uniform nanocomposite film

Co–ZnO metal-semiconductor nanocomposite films have drawn a growing number of attention due to their significant room temperature (RT) magnetoresistance (MR) effect. In this paper, Co–ZnO non-uniform nanocomposite films with high crystallinity of ZnO matrix have been prepared by controlling substrate temperature. With the increase of substrate temperature, the Co particles grow and gradually aggregated into ferromagnetic clusters, which leads to an increase in saturation magnetization (Ms) from 5.8 to 6.7 kGs. Moreover, the growth of ferromagnetic clusters results in the formation of cluster-particle current paths and isolated magnetic particles, which have less contribution to the MR, causing the separation between MR curve and -(M/Ms)2 curve. This phenomenon induces a broadening of the MR curve, which modulates the shift of the MR field sensitivity (FS) peak toward higher fields. When the substrate temperature is 250 °C, high ZnO matrix crystallinity, -MR value (2.6%) and effective modulation of MR FS in Co–ZnO non-uniform nanocomposite films can be achieved simultaneously. It provides a reference for the application and modification of Co–ZnO MR devices.

Effects of Partial Manganese Substitution by Cobalt on the Physical Properties of Pr0.7Sr0.3Mn(1-x)CoxO3 (0 ≤ x ≤ 0.15) Manganites.

We have investigated the structural, magnetic, and electrical transport properties of Pr0.7 Sr0.3 Mn(1-x)Cox O3 nanopowders (x = 0, 0.05, 0.10 and 0.15). The Pechini Sol-gel method was used to synthesize these nanopowders. X-ray diffraction at room temperature shows that all the nano powders have an orthorhombic structure of Pnma space group crystallography. The average crystallite size of samples x = 0, 0.05, 0.10, and 0.15 are 33.78 nm, 29 nm, 33.61 nm, and 24.27 nm, respectively. Semi-quantitative chemical analysis by energy dispersive spectroscopy (EDS) confirms the expected stoichiometry of the sample. Magnetic measurements indicate that all samples show a ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature TC gradually decreases (300 K, 270 K, 250 K, and 235 K for x = 0, 0.05, 0.10, and 0.15, respectively) with increasing Co concentrations. The M-H curves for all compounds reveal the PM behavior at 300 K, while the FM behavior characterizes the magnetic hysteresis at low temperature (5 K). The electrical resistivity measurements show that all compounds exhibit metallic behavior at low temperature (T < Tρ) well fitted by the relation ρ = ρ0 + ρ2T2 + ρ4.5T4.5 and semiconductor behavior above Tρ (T > Tρ), for which the electronic transport can be explained by the variable range hopping model and the adiabatic small polaron hopping model. All samples have significant magnetoresistance (MR) values, even at room temperature. This presented research provides an innovative and practical approach to develop materials in several technological areas, such as ultra-high density magnetic recording and magneto resistive sensors.

Role of cationic size mismatch and effect of disorder in mixed valent manganites

Comparative studies of structure, magnetism, and magnetoresistance (MR) have been carried out in A-site ordered NdBaMn2O6 (O-NB), A-site disordered NdBaMn2O6 (D-NB) and A-site disordered NdCaMn2O6 (D-NC). O-NB, where A-site cations, Nd3+ and Ba2+ (of different ionic sizes) are arranged periodically, undergoes structural transition with temperature, while no structural change is present in D-NB where A-site cations are arranged randomly. However, structural transitions are observed in D-NC where Nd3+ and Ca2+ have similar ionic sizes. Magnetization (M) data shows O-NB has AFM ground state associated with a lower structurally symmetric phase and an FM ground state is observed for D-NB with higher structural symmetry. However, AFM ground state is observed in D-NC similar to that of O-NB. Both the disorder systems exhibit semiconductive transport characteristics over the entire temperature range. The resistivity data of disorder compounds have been fitted with different theoretical models to elucidate the conduction process in these systems. Further, MR studies depict a three times higher value of MR in both disorder compounds compared to that of order one. However, the behavior of MR with H is different for D-NB and D-NC, implying a different origin of this large MR in these compounds. We believe that the different magnetic ground state of D-NB and D-NC is the possible origin of their distinct MR behavior to the magnetic field.

Measurement System for Short-Pulsed Magnetic Fields.

A measurement system based on the colossal magnetoresistance CMR-B-scalar sensor was developed for the measurement of short-duration high-amplitude magnetic fields. The system consists of a magnetic field sensor made from thin nanostructured manganite film with minimized memory effect, and a magnetic field recording module. The memory effect of the La1-xSrx(Mn1-yCoy)zO3 manganite films doped with different amounts of Co and Mn was investigated by measuring the magnetoresistance (MR) and resistance relaxation in pulsed magnetic fields up to 20 T in the temperature range of 80-365 K. It was found that for low-temperature applications, films doped with Co (LSMCO) are preferable due to the minimized magnetic memory effect at these temperatures, compared with LSMO films without Co. For applications at temperatures higher than room temperature, nanostructured manganite LSMO films with increased Mn content above the stoichiometric level have to be used. These films do not exhibit magnetic memory effects and have higher MR values. To avoid parasitic signal due to electromotive forces appearing in the transmission line of the sensor during measurement of short-pulsed magnetic fields, a bipolar-pulsed voltage supply for the sensor was used. For signal recording, a measurement module consisting of a pulsed voltage generator with a frequency up to 12.5 MHz, a 16-bit ADC with a sampling rate of 25 MHz, and a microprocessor was proposed. The circuit of the measurement module was shielded against low- and high-frequency electromagnetic noise, and the recorded signal was transmitted to a personal computer using a fiber optic link. The system was tested using magnetic field generators, generating magnetic fields with pulse durations ranging from 3 to 20 μs. The developed magnetic field measurement system can be used for the measurement of high-pulsed magnetic fields with pulse durations in the order of microseconds in different fields of science and industry.

Room-temperature magnetoresistance in an all-antiferromagnetic tunnel junction.

Antiferromagnetic spintronics1-16 is a rapidly growing field in condensed-matter physics and information technology with potential applications for high-density and ultrafast information devices. However, the practical application of these devices has been largely limited by small electrical outputs at room temperature. Here we describe a room-temperature exchange-bias effect between a collinear antiferromagnet, MnPt, and a non-collinear antiferromagnet, Mn3Pt, which together are similar to a ferromagnet-antiferromagnet exchange-bias system. We use this exotic effect to build all-antiferromagnetic tunnel junctions with large nonvolatile room-temperature magnetoresistance values that reach a maximum of about 100%. Atomistic spin dynamics simulations reveal that uncompensated localized spins at the interface of MnPt produce the exchange bias. First-principles calculations indicate that the remarkable tunnelling magnetoresistance originates from the spin polarization of Mn3Pt in the momentum space. All-antiferromagnetic tunnel junction devices, with nearly vanishing stray fields and strongly enhanced spin dynamics up to the terahertz level, could be important for next-generation highly integrated and ultrafast memory devices7,9,16.

Variation of structural and magnetic properties of mixed-valent manganites through A-site cationic ordering

Effect of A-site cationic ordering on structural, transport and magnetic properties of mixed-valent perovskite manganite NdBaMn2O6 has been studied. Three samples of same chemical composition NdBaMn2O6 but with different degrees of A-site ordering (92 %, 60 %, 28 %) were prepared by tuning the synthesis conditions. At higher temperatures, all the compounds possess the same crystallographic phase (P4/mmm). However, temperature (T) dependent X-ray diffraction data reveals that different types of crystallographic phase transitions depends on the degree of ordering of the A-site cations Nd3+ and Ba2+. For example, the maximum ordered compound undergoes multiple structural phase transitions (from P4/mmm to Cmmm to P21am) with decreasing T, whereas the disordered compound retains the high-T crystal structure (P4/mmm) throughout the studied temperature range. Resistivity measurements shows that although both the compounds (ordered and disordered) are insulating, the mechanism of charge transport is different for the two compounds. Similarly the magnetic properties and colossal magnetoresistance also depend on the degree of ordering. Cationic disorder suppresses the long-range antiferromagnetic order and enhances ferromagnetic correlations at lower temperature; which (ferromagnetic correlation) is accompanied with larger value of saturation magnetic moment while ferromagnetic TC too shifts to higher temperature with increasing disorder. Disordered system also exhibits a larger value of magnetoresistance at low temperature compared to the ordered counterpart.

Polycrystalline La0.66Gd0.04Ca0.3MnO3 for magnetic-response applications: concurrent anisotropic magnetoresistance and magneto-transport under a low magnetic field

Polycrystalline La0.66Gd0.04Ca0.3MnO3 with a large anisotropic magnetoresistance (−30%) value achieved under a magnetic field of 1 T.

Спиновый угол Холла в гетероструктурах иридат/манганит

We present results on experimental determination of spin-Hall angle theta_SH in the SrIrO3/La0.7Sr0.3MnO3 heterostructure with nanometer-thick films. From longitudinal magnetoresistance value of spin-Hall angle was estimated thetaL_SH ≈ 0.04 ± 0.01, from the transverse thetaT_SH ≈0.35±0.06. Decreasing the temperature from room to T= 165 K, the transverse magnetoresistance decreased, and at temperatures T&lt;150 K it was not detected within the measurement error. For comparison, we measured also a single SrIrO3 film which did not demonstrate magnetoresistance.

Room-Temperature Spin Transport in Metal Nanocluster-Based Spin Valves.

As a new type of inorganic-organic hybrid semiconductor, quantum-confined atomically precise metal nanoclusters (MNCs) have been widely applied in the fields of chemical sensing, optical imaging, biomedicine and catalysis. Herein, we successfully design and fabricate the first example of MNC-based spin valves (SVs) that exhibit remarkable magnetoresistance (MR) value up to 1.6 % even at room temperature (300 K). The concomitant photoresponse of MNC-based SVs unambiguously confirms that the spin-polarized electron transmission takes place across the MNC interlayer. Furthermore, the spin-dependent transport property of MNC-based SVs is largely varied by changing the atomic structure of MNCs. Both experimental proofs and quantum chemistry calculations reveal that the atomic structure-discriminative spin transport behavior is attributed to the distinct spin-orbit coupling (SOC) effect of MNCs.

Room‐Temperature Spin Transport in Metal Nanocluster‐Based Spin Valves

AbstractAs a new type of inorganic‐organic hybrid semiconductor, quantum‐confined atomically precise metal nanoclusters (MNCs) have been widely applied in the fields of chemical sensing, optical imaging, biomedicine and catalysis. Herein, we successfully design and fabricate the first example of MNC‐based spin valves (SVs) that exhibit remarkable magnetoresistance (MR) value up to 1.6 % even at room temperature (300 K). The concomitant photoresponse of MNC‐based SVs unambiguously confirms that the spin‐polarized electron transmission takes place across the MNC interlayer. Furthermore, the spin‐dependent transport property of MNC‐based SVs is largely varied by changing the atomic structure of MNCs. Both experimental proofs and quantum chemistry calculations reveal that the atomic structure‐discriminative spin transport behavior is attributed to the distinct spin‐orbit coupling (SOC) effect of MNCs.

Half-Metallic Heusler Alloy/MoS2 Based Magnetic Tunnel Junction.

Integration of half-metallic materials and 2D spacers into vertical magnetoresistive spin valves may pave the way for effective low-power consumption storage and memory technologies. Driven by the recent successful growth of graphene/half-metallic Co2Fe(Ge1/2Ga1/2) (CFGG) heterostructure, here we report a theoretical investigation of magnetic tunnel junction (MTJ) based on the ferromagnetic CFGG Heusler alloy and the MoS2 spacer of different thicknesses. Using ab initio approach, we demonstrate that the inherent ferromagnetism of CFGG is preserved at the interface, while its half-metallicity is recovering within few atomic layers. Ballistic transport in CFGG/MoS2/CFGG MTJ is studied within the nonequilibrium Green's function formalism, and a large magnetoresistance value up to ∼105% is observed. These findings support the idea of effective spintronics devices based on half-metallic Heusler alloys and highly diversified transition metal dichalcogenide family.

Violation of Kohler's rule at the charge density wave transition in 1T-TiSe2

The Kohler scaling of magnetoresistance (MR) is examined across the charge-density-wave (CDW) transition of 1T-TiSe2 microflakes. The normalized MR value vs (B/ρ0)2 showed linear dependence, where B is the magnetic field and ρ0 is the resistivity at zero magnetic field. However, all MR-(B/ρ0)2 curves at various temperatures were not coincident with each other, demonstrating the violation of Kohler's rule. The Kohler slope, K = dMR/d[(B/ρ0)2], and the MR value reached a minimum at the CDW transition temperature, TCDW. The nonmonotonous relationship between the Kohler slope and the Hall coefficient was observed, indicating a nonuniform electron scattering rate on the Fermi surface. The MR value satisfied the scaling laws of ∼|T − TCDW|1.35 and ∼|T − TCDW|0.62 below and above TCDW, respectively. Our results highlight magnetotransport properties of the 1T-TiSe2 microflakes in the critical region of the CDW phase transition.

Magnetoresistance enhancement in a perpendicular (Co/Pt)4/Co/IrMn/(Co/Pt)2/Co structure

We investigate the magnetoresistance (MR) effect and magnetic properties in (Co/Pt)4/Co/IrMn (SFM) and (Co/Pt)4/Co/IrMn/(Co/Pt)2/Co (DFM) structures with (Co/Pt)4/Co and (Co/Pt)2/Co multilayers having a perpendicular magnetic anisotropy. Despite the exchange bias field, the antiferromagnetic IrMn layer itself influences the coercivity (Hc) and MR differently for both types of structures when the IrMn layer is thin. A suppressed Hc and an enhanced MR in the DFM samples are obtained compared with those in the SFM samples. The maximum MR reaches up to (0.6 ± 0.1)% when the IrMn thickness (tIrMn) of the DFM samples varies from 1.5 to ∼5 nm, but the MR value of the SFM samples remains (0.1 ± 0.05)% with the same tIrMn range. The suppressed Hc and the enhanced MR in the DFM samples may be due to the formation of an antiferromagnetic-type contact when large antiferromagnetic domains in the IrMn layer are sandwiched by (Co/Pt)4/Co and (Co/Pt)2/Co multilayers.