Maximum Magnetoresistance Value Research Articles

Study of the electrophysical and magnetic properties of a Dirac 3D semimetal Cd3As2 with nanogranules of MnAs

We report on the main results of studying the electrical and magnetoresistance (MR) of a composite material consisting of 70 % mol. Dirac semi-metal Cd3As2 and 30 % mol. ferromagnet MnAs at pressures up to 50 GPa in a diamond anvil cell with a «rounded cone-flat» type anvils, as well as magnetization at hydrostatic pressures up to 6 GPa in a toroid-shaped high-pressure cell, both at room temperature and in the temperature range of 180 – 350 K at atmospheric pressure. A mixture of methanol and ethanol in a ratio of 4:1 was used as a pressure transmitting medium. Elemental analysis of Cd3As2 + 30 % mol MnAs composites showed that much of the volume is occupied by the Cd3As2 phase. The proportion of MnAs phase inclusions is less than 5 %. The feature of Cd3As2 + MnAs is the presence of a significant region of non-mixing of the Cd3As2 and MnAs phase melts. A negative MR was revealed with increasing pressure in the entire studied baric zone. The maximum negative MR is observed in the baric zone of 22 – 26 GPa. Further increase in the pressure up to the maximum level result in the appearance of several extrema on the ΔR/R0(P) curve, with negative MR not exceeding 4 %. Upon pressure release from 50 GPa, the baric dependence of ΔR/R0(P) is characterized by an inversion of the MR sign: at pressures around 40 GPa, a negative MR is replaced by a positive MR, and at around 20 GPa, the maximum value of positive MR of ~5.3 % is observed. Signs of the instability of the monoclinic structure of Cd3As2 resulted from its partial decomposition upon decompression were revealed. The results obtained can be used in spintronics when using appropriate composite materials.

Electric-field-induced epitaxial breakdown and emergent magnetoresistance due to strong oxygen reduction in Ca-doped BiFeO3

We study the structural and transport properties of a heavily oxygen-reduced region that is formed by electrical injection of a large amount of oxygen vacancies into a ${\mathrm{Bi}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{FeO}}_{3\ensuremath{-}\ensuremath{\delta}}$ thin film. In electroforming, the epitaxial as-grown state is transformed into a disordered, polycrystalline phase. Nonohmic current-voltage relations, which can be interpreted as a space-charge-limited conduction, appear at low temperatures. As temperature increases, the curvature of the current-voltage relationship gradually changes to be nearly ohmic at and above 100 K. The maximum value of magnetoresistance, as large as \ensuremath{-}2.6% at 90 kOe, is attained at the same temperature of \ensuremath{\sim}100 K, which is significantly larger than \ensuremath{-}0.1% at 25 K and \ensuremath{-}1.3% at 300 K.

High room-temperature TCR and MR of La1-xSrxMnO3 thin films for advanced uncooled infrared bolometers and magnetic sensors

Perovskite manganese films had promising applications in the field of photoelectronic materials and devices. However, the utilization of manganese films remained severely challenging due to high fabrication cost and inferior electrical and magnetic properties. Herein, La1-xSrxMnO3 (LSMO) thin films were fabricated on La0.3Sr0.7Al0.65Ta0.35O3 (LSATO) substrates using a facile sol–gel spin-coating technique. All the LSMO films displayed (001)-orientation with orthorhombic structure. The LSMO films exhibited high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) values at room-temperature. The maximum TCR value was 10.4 % K−1 (301.2 K, for x = 0.175). This result can be attributed to high carrier concentration and mobility of optimal × content LSMO films with low film-substrate lattice mismatch (-0.4%), leading to low resistivity, and thus, increased TCR value. The maximum MR value reached 42.85% (290.95 K, for x = 0.150). The LSMO films with high room-temperature TCR and MR values are potential materials for advanced uncooled infrared bolometers and magnetic sensors.

Conductivity of pressed powders of chromium dioxide with spin-dependent electron tunneling: The effect of thickness and composition of dielectric layers

The resistive, magnetoresistive, and magnetic properties for nine compacted CrO2 powder samples synthesized by hydrothermal method from chromic anhydride were studied. The proposed new synthesis method allows adjusting the thickness of the dielectric shells on the surface of CrO2 nanoparticles. The powders consisted of either rounded nanopartides (with an average diameter of ≈ 120 nm) or needle-like crystals (≈22.9 nm in diameter and 302 nm long). In all cases, nanoparticles were covered by dielectric shells of varied thickness and composition (for example, chromium oxide Cr2O3 or chromium oxyhydroxide β-CrOOH). The effect of material properties and thickness of the intergranular dielectric layers, as well as the shape of CrO2 nanoparticles, on the magnitude of the tunnel resistance and magnetoresistance (MR) of compacted powder samples was investigated. For all the samples studied, the nonmetallic temperature behavior of the resistance and the giant negative tunneling MR were detected at low temperatures. The maximum values of MR at T ≈ 5 K and relatively small magnetic field (H = 0.5 T) were approximately 37%. With increasing temperature, the MR rapidly decreased (down to ≈1% at H = 1 T, T ≈ 200 K).

Magnetoresistance of CoFeNi/Cu Superlattices Differing in the Ferromagnetic Alloy Composition

Abstract—The structure and magnetoresistive properties of Ta(5 nm)/NiFeCr(5 nm)/[FM(tFM)/Cu(2.2 nm)]n/ Ta(5 nm) superlattices prepared by magnetron sputtering are studied in this work. The ferromagnetic layer thickness tFM is varied in a 1.1–1.5 nm range. The Co90Fe10, Co85Fe12Ni3, Co77Fe17Ni6, and Co70Fe20Ni10 alloys with an fcc structure and close saturation magnetization values are used as the ferromagnetic (FM) materials. It is shown that, as the Ni and Fe contents in the CoFeNi alloy increase, the magnetoresistance of superlattices containing eight bilayers remains high and equal to 24–28%; in this case, the twofold decrease in the hysteresis occurs. As the number of bilayers in the superlattices, which contain CoFeNi alloys differing in composition increases to 12, the close values of magnetoresistance 30–31% are obtained. The correlation between the saturation magnetization of the ferromagnetic material of superlattice layers and maximum value of magnetoresistance is discussed.

Tunable low-field magnetoresistance properties in (La0.7Ca0.3MnO3)1−x:(CeO2)x vertically aligned nanocomposite thin films

Vertically aligned nanocomposite (VAN) (La0.7Ca0.3MnO3)1−x:(CeO2)x thin films have been deposited on SrTiO3 (001) substrates by pulsed laser deposition. Enhanced low-field magnetoresistance properties and tunable metal-insulator transition temperature (TMI) have been demonstrated via modulating the composition of (La0.7Ca0.3MnO3)1−x:(CeO2)x (x = 0, 0.05, 0.1, and 0.2). By increasing the atomic percentage of the CeO2 phase to 20%, a maximum magnetoresistance value of 51.8% can be achieved and the TMI value can be tuned from 113 K to 210 K. The enhanced magnetoresistance properties are attributed to the disordered grain boundary and tunneling structure generated by the insulating CeO2 phase. The change in the TMI value is attributed to the strain state in the La0.7Ca0.3MnO3 phase. Furthermore, high ferromagnetic anisotropy and enhanced magnetization have been demonstrated in the VAN system. This work demonstrates the power of multifunctionalities and property tuning in VAN thin films.

Effect of Silver Substitution on Electrical Transport and Magnetoresistance of La0.8Ca0.2MnO3

In this work, we have investigated the effect of silver substitution on electrical transport behavior and magnetoresistance of La0.8-xAgxCa0.2MnO3 (x = 0 and 0.05). Preparation and study of structural and microstructure of both samples have been reported on previous work. Temperature-dependent resistivity has been measured at temperature range of 15-285 K with zero field cooling. Magnetoresistance effect has been measured at 15, 100, and 285 K with magnetic field up to 1 T. The electrical transport behavior of both samples are quite well described by a theory based on the Percolation model. The electrical conduction mechanism at low temperature can be explained by a theory based on Kondo-like spin-dependent scattering, electron-electron, electron–magnon, and electron-phonon scattering. It was found that silver substitution increases the metal-insulator transition temperature (TM-I) from 197.55 to 277.56 K, and Curie temperature (TcMod) from 217.25 to 278.65 K. Moreover, the maximum magnetoresistance value of both samples was obtained at 15 K.

Electrical, magnetic and magnetotransport properties of Na and Mo doped Ca3Co4O9 materials.

We report the electrical, magnetic and magnetotransport properties of Na and Mo dual doped Ca3−2xNa2xCo4−xMoxO9 (0 ≤ x ≤ 0.15) polycrystalline samples. The results indicate that the strength of ferrimagnetic interaction decreases with increase in doping, as is evident from the observed decrease in Curie temperatures (TC). The substitution of non-magnetic Mo6+ ions (4d0) in CoO2 layers and the presence of oxygen vacancies are responsible for decrease in ligand field strength, which results in an enhanced magnetization in the low doped x = 0.025 sample due to a change from the low spin to partial high spin electron configuration. The electrical resistivity of samples exhibits a semiconducting-like behavior in the low temperature range, a strongly correlated Fermi liquid-like behavior in the intermediate temperature range, and an incoherent metal-like behavior in the temperature range 210–300 K. All the samples show a large negative magnetoresistance (MR) at low temperature with a maximum MR value of −59% for the x = 0.025 sample at 2 K and 16 T applied field. The MR values follow the observed trend in magnetization at 5 K and sharply increase below the Curie temperatures of the samples, suggesting that the ferrimagnetic interactions are mainly responsible for the decrease in electrical resistivity under an applied magnetic field.

Large positive magnetoresistance of graphene at room temperature in magnetic fields up to 0.5 T

Graphene films were grown on an iron film catalyst deposited on oxidized silicon substrate, using the low-pressure chemical vapor deposition. Subsequently the iron film was dissolved with an aqueous solution of iron nitrate. The structures consisting of quasi-suspended graphene on reaction products of an iron film with iron nitrate were obtained. Magnetoresistance properties of the structures were investigated at a room temperature, and the positive magnetoresistance was observed. The maximum magnetoresistance value was 100% in the magnetic field of 0.5T. The dependence of magnetoresistance on the magnetic field was quasi-linear in the range of 0.07–0.5T.

Enhanced room-temperature MR and TCR in polycrystalline La0.67(Ca0.33−xSrx)MnO3 ceramics by oxygen assisted sintering

Polycrystalline La0.67(Ca0.33-xSrx)MnO3 (LCSMO, x = 0, 0.03, 0.06, 0.09, 0.12, and 0.15) ceramics were prepared by sol-gel method. Microstructures, electrical/magnetic transport properties, temperature coefficient of resistance (TCR) and magnetoresistance (MR) behaviors, were all investigated. X-ray diffraction (XRD) results showed that all samples crystallized in single phases without detectable secondary phases. At Sr doping (x) above 0.12, crystal structures transformed from orthorhombic phase (space group of Pnma) to rhombohedral phase (space group of R3̅c). As x content further rose, metal-insulator transition temperature (Tp) increased and maximum values of TCR and MR decreased. Further data revealed that TCR and MR peaks were controlled by Sr doping level x. In addition, room temperature MR and TCR of LCSMO ceramics were enhanced under oxygen assisted sintering. At Sr doping x = 0.09, the value of Tp attained room temperature (301.8K), and the maximum values of TCR and MR reached 10.5% K−1 and 43.0%, respectively. These properties were related to combination of double exchange (DE) and Jahn−Teller effects. LCSMO materials may have promising future use in photoelectric (uncooled bolometer or infrared detectors) or magnetic devices (uncooled magnetic sensors) at room temperature.

Integration of antiferromagnetic Heusler compound Ru2MnGe into spintronic devices

We report on the integration of an antiferromagnetic Heusler compound acting as a pinning layer into magnetic tunneling junctions (MTJs). The antiferromagnet Ru2MnGe is used to pin the magnetization direction of a ferromagnetic Fe layer in MgO based thin film tunneling magnetoresistance stacks. The samples were prepared using magnetron co-sputtering. We investigate the structural properties by X-ray diffraction and reflection, as well as atomic force and high-resolution transmission electron microscopy. We find an excellent crystal growth quality with a low interface roughnesses of 1–3 Å, which is crucial for the preparation of working tunneling barriers. Using Fe as a ferromagnetic electrode material, we prepared magnetic tunneling junctions and measured the magnetoresistance. We find a sizeable maximum magnetoresistance value of 135%, which is comparable to other common Fe based MTJ systems.

Easy synthesis and electric, magneto-transport and magnetic properties of double perovskite La2CoMnO6 compound

We report synthesis of double perovskite La2CoMnO6 compound by a simple solid state reaction method. The samples sintered at different temperatures showed single phase nature with monoclinic P21/n space group. The phase purity was confirmed through the presence of characteristic Raman scattering modes. The samples exhibited semiconducting behavior without any anomaly in the temperature range 125 K ≤ T ≤ 300 K. The maximum magnetoresistance value at low temperature was around 40 %. The electric and magneto-transport behaviors were governed by variable range hopping mechanism. A single paramagnetic to ferromagnetic transition and well saturated hysteresis loops, indicative of ordered phase were observed in these samples.

The Effect of Mn Doping on the Structure, Magnetic Properties, and Magnetoresistance of Fe-Cu Thin Films

Deposited on the glass substrate by direct current (dc) magnetron sputtering, the Fe-Cu-Mn thin film consisting of Fe nanoparticles embedded in a Cu matrix was treated by vacuum annealing. The effects of Mn doping and annealing temperature on the structure, magnetic properties, and magnetoresistance were investigated. The as-deposited films had flat, compact surfaces and face-centered cubic (fcc) structure. The grain size of Fe increased with the annealing temperature. With the Mn doping, the size increased first and then decreased. The Mn content exists in an amorphous state in the nanocomposite films, and it is homogeneously distributed between the Fe nano-grains, which increase grain growth and obtain isolated Fe particles with uniform size. Not all of the Mn atoms diffuse into the nano-sized Fe particles until the Mn content reaches 10 at.%. The easy magnetization direction of the Fe-Cu-Mn films is in plane rather than out of plane. Coercivity, remanent magnetization, remanence ratio, and hysteresis losses are associated with increasing content of Mn in the samples. As Mn doping occurs, the magnetoresistance (MR) of the Fe-Cu film is reduced and the best temperature corresponding to the maximum value of MR is ∼350 °C.

Influence of anisotropic strain relaxation on the magnetoresistance properties of epitaxial Fe3O4 (110) films

We studied Fe3O4 (110) films grown epitaxially on MgO (110) substrates using oxygen plasma assisted molecular beam epitaxy. The films with thickness of 30–200 nm showed anisotropic in-plane partial strain relaxation. Magneto resistance (MR) measurements with current and magnetic field along ⟨001⟩ direction showed higher MR compared to ⟨1¯10⟩ direction. Maximum value of MR was measured at Verwey transition temperature for both directions. We explain the observed anisotropy in the MR on the basis of the effects of anisotropic misfit strain, and the difference between the density of antiferromagnetically coupled antiphase boundaries formed along ⟨001⟩ and ⟨1¯10⟩ crystallographic directions, suggesting the dependence of spin polarisation on the anisotropic strain relaxation along the said crystallographic directions.

Tuning martensitic transformation, large magnetoresistance and strain in Ni 50−x Fe x Mn 36 Sn 14 Heusler alloys

Abstract We have investigated the martensitic transformation, exchange bias, magnetoresistance (MR) and strain in Ni 50− x Fe x Mn 36 Sn 14 ( x =1, 2, 3, 4) Heusler alloys. With the increase of Fe content, the austenite phase could be stabilized with L 2 1 structure and hence the martensitic transition shifts to a lower temperature and finally disappears. This behavior can be understood by the weakening of Ni–Mn hybridization to suppress AFM interactions and enhancement of Fe–Fe ferromagnetic exchange interactions. The same reason can account for the slight decrease of exchange bias field ( H EB ) with the increase of the Fe content from x =1 to 2 and the disappearance of H EB for x =3. We observed MR effect for x =3, and a maximum MR value of −52% was achieved, which can be explained by the change in the electronic structure during martensitic transformation induced by the magnetic field. In addition, a large strain of 0.207% in Ni 49 Fe 1 Mn 36 Sn 14 was observed due to the changes of lattice parameters during the martensitic transformation induced by temperature.

Large field-induced magnetocaloric effect and magnetoresistance in ErNiSi

Large magnetocaloric effect (MCE) and magnetoresistance (MR) together with negligible hysteresis loss have been observed in ErNiSi compound, which undergoes metamagnetic transition at low temperatures. Magnetization, heat capacity, and resistivity measurements confirm the metamagnetic transition. Both MCE and MR follow H2 dependence in the paramagnetic regime. The maximum value of isothermal entropy change (ΔSM) and MR for a field change of 50 kOe are found to be 19.1 J/kg K and ∼34%, respectively. Large MCE with negligible magnetic hysteresis loss could make this material promising for low temperature magnetic refrigeration.

Magnetisation and magnetoresistance of Mo/Fe/Co superlattices

AbstractIn this paper, we present experimental studies of the structure, magnetic behavior and magnetoresistance of magnetic superlattices (MSL) [Mo(12Å)Fe(xÅ)Co(21Å)]*100 (x=4÷43). MSLs have been obtained by cathode sputtering with oscillating electrons on the substrate of mica (muscovite). MSLs investigated at room temperature are soft ferromagnets with induced in‐plane magnetic anisotropy. Changes in the spontaneous magnetization Iso and coercive force Hc, depending on the thickness of Co layers, are of oscillatory behavior, which is apparently because of the interference effects of electron waves in the spacers and interfaces. Stepped shape of the measured hysteresis loops for some MSLs, is apparently determined by the vortex behavior of the clusters magnetic moments, located in the sample plane, that is confirmed by measurements carried out on the scanning probe microscope. The observed high values of Iso, normalized to the content of Fe and Co, exceeding Iso(Fe)=1710 Gs may be observed due to increasing values of spin and orbital magnetic moments of Fe and Co in the cluster formations and in the interfaces in the states of low‐dimensional local atomic environment, as well as the possible formation of ferromagnetic order in Mo clusters. Studies of resistance and magnetoresistance (MR) of the samples at temperatures from 10 K to 290 K show semiconducting behavior of resistance and a positive sign of the magnetoresistance. The maximum value of MR for a sample of [Mo (12A) Fe (16A) Co (21A)] x100 was 0.04% for [Mo (12A) Fe (10A) Co (21A)]x100 ‐ 0.5%. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of superconducting spacer layer thickness on magneto-transport and magnetic properties of La0.7Sr0.3MnO3/YBa2Cu3O7/La0.7Sr0.3MnO3 heterostructures

We have studied the magneto-transport and magnetic properties of LSMO/YBCO/LSMO trilayers on LaAlO3 (001) substrate, deposited using pulsed laser deposition technique. From x-ray diffraction measurements, it is confirmed that the grown trilayer films are single phase natured. The temperature dependent resistivity shows a metallic behavior below 350 K. At low temperature from resistivity fitted data, we observe that electron-electron, electron-phonon, and electron-magnon interactions are the main factors for scattering of carriers. The ferromagnetic LSMO layers suppress the critical temperature of YBCO spacer layer. We observe maximum magnetoresistance value ∼49% at 250 K for LSMO(200 nm)/YBCO(50 nm)/LSMO(200 nm) trilayer. Magnetization measurements reveal that at room temperature the YBCO spacer layer is allowing the LSMO layers to interact antiferromagnetically.

Nanocomposite films with magnetic field sensing properties

La0.67Sr0.33MnO3 (LSMO) and LSMO:ZnO nanocomposite thin films were fabricated on SiO2/Si and (0001) Al2O3 substrates through solution deposition routes. The LSMO grain size reduced in the composite films as compared to that in pure LSMO film resulting in a larger volume fraction of grain boundaries. Further, compositional or magnetic disorder at the grain boundary region resulted in a reduction of the ferromagnetic-paramagnetic and metal–insulator transition temperatures in LSMO:ZnO films. The magnetoresistance (MR) behavior in the composite films was revealed to be dominated by extrinsic effects with large values of MR at low temperatures and low applied fields. A maximum low-field MR value of −23.9% was observed at 0.5T and 10K with the field applied parallel to the current for LSMO:ZnO film on Al2O3, with a maximum field sensitivity of 632%/T.

Structural, electrical, and magnetic properties of Ce doped La0.7Ca0.3MnO3 thin films

We have studied the structural, transport, and magnetic properties of La0.7Ca0.3−xCexMnO3 (x = 0.0, 0.025, 0.05, 0.1, and 0.15) manganite thin films on LaAlO3 (100) substrate prepared by pulsed laser deposition technique. The grown films are single phase and epitaxial in nature as revealed by x-ray diffraction and in-plane phi-scan. The temperature dependent resistivity measurements of these films reveal a metal–semiconductor transition at TP and transition temperature is found to shift lower temperature with Ce doping. Resistivity data at high temperature have been fitted with the variable range hopping model to estimate the density of states at Fermi level {N (EF)}, while at low temperature electron–electron, electron–phonon, and electron-magnon processes contribute to scattering of carriers. It was observed that N(EF) decreases with Ce doping leads to a decrease in conductivity of the Ce doped samples. We have observed maximum magnetoresistance value ∼90% near the TP. Magnetization measurements reveal that long-range ferromagnetic ordering in all samples and that saturation magnetic moment increases as x increases.