Considerable Magnetoresistance Research Articles

Robust Crystal Phase Separation with Distinct Charge, Orbital, and Spin Orders in AgMn7O12.

An AA'3B4O12-type A-site-ordered quadruple perovskite oxide AgMn7O12 was prepared by high-pressure and high-temperature methods. At room temperature, the compound crystallizes into a cubic Im3̅ symmetry with a charge distribution of AgMn33+Mn43.5+O12. With the temperature decreasing to TCO,OO ≈ 180 K, the compound undergoes a structural phase transition toward a monoclinic C2/m symmetry, giving rise to a B-site charge- and orbital-ordered AgMn33+Mn23+Mn24+O12 phase. Moreover, this charge-/orbital-ordered main phase coexists with the initial cubic AgMn33+Mn43.5+O12 phase in the wide temperature range we measured. The charge-/orbital-ordered phase shows two antiferromagnetic phase transitions near 125 and 90 K, respectively. Short-range ferromagnetic correlations are found to occur for the initial B-site mixed cubic phase around 35 K. Because of the robust phase separation, considerable magnetoresistance effects are observed below TCO,OO in AgMn7O12.

Magnetism, magnetocaloric and magnetotransport properties of Dy5NiSi2 alloy

Systematic investigations were carried out on the magnetic, thermodynamic, transport and magnetocaloric properties of arc melted Dy5NiSi2 compound. The polycrystalline compound shows two ferromagnetic (FM) transitions at T1 = 44 K and T2 = 72 K, respectively. The isothermal magnetization curves of T = 2–40 K reveal the presence of metamagnetic transition at a critical field around 4 T. The magnetic entropy change (ΔSM) computed from both isothermal magnetization and heat capacity data shows a maximum of 16.3 J/kg K at 72 K for a field change of 0–9 T. Also, the presence of two successive ferromagnetic transitions at T1 = 44 K and T2 = 72 K displays a table like magnetocaloric effect in a wide temperature range 29–137 K (ΔTcycle = 108 K) with a refrigerant capacity of 580 J/kg for a field change of 0–9 T. It also exhibits considerable negative magnetoresistance of 11% in 9 T at 2 K. Hence, the results on Dy5NiSi2 alloy are interesting for low-temperature magnetic refrigeration.

Inverse magnetocaloric effect and magnetoresistance associated with martensitic transition for Cu‐doped Ni‐Mn‐In Heusler alloy

In this study, we reported the influence of replacing Cu for Ni on the crystal structure, martensitic transformation, and magnetic properties for polycrystalline Ni50−xCuxMn37In13 (x = 5 and 7) quaternary alloys. It was found that the studied alloys undergo a first‐order martensitic transformation from ferromagnetic austenite to paramagnetic martensite near room temperature. With increasing Cu content, the martensitic transformation significantly shifts toward a lower temperature, and fully splits off from the Curie transition of austenite, which enhances the difference in magnetization between the two phases for the alloy with x = 7. Moreover, both inverse magnetocaloric and magnetoresistance effects during reverse martensitic transformation were also studied in these two alloys. In comparison to Ni50−xCuxMn37In13 with x = 5, an optimized refrigerant capacity (∼100 J kg−1) and a considerable magnetoresistance (47%) were obtained in Ni43Cu7Mn37In13 alloy for the magnetic field change of 30 kOe. In addition, the magnetic measurements with hydrostatic pressure demonstrate that the magnetoresistance in this system mainly arises due to the electron‐lattice scattering triggered by structural transition.

Transport and pinning properties of Ag-doped FeSe0.94

We investigated the superconducting transition and the pinning properties of undoped and Ag-doped FeSe0.94 at magnetic fields up to 14 T. We established that, due to Ag addition, the hexagonal phase formation in melted FeSe0.94 samples is suppressed and the grain connectivity is strongly improved. The obtained superconducting zero-field transition becomes sharp, with a transition width below 1 K. Tc and the upper critical field were found to increase, while the normal-state resistivity was significantly reduced, becoming comparable with that of FeSe single crystals. In addition, a considerable magnetoresistance was observed due to Ag doping. The resistive transition of undoped and Ag-doped FeSe0.94 is dominated by a thermally activated flux flow. From the activation energy U versus H dependence, we found a crossover from single-vortex pinning to a collective-creep pinning behavior by increasing the magnetic field.

High pressure synthesis and properties of Bi0.5Pb0.5CrO3: A novel Cr4+/Cr3+ perovskite

We have synthesized a new Bi0.5Pb0.5CrO3 perovskite phase by means of a high pressure reaction at 70kbar and 1000°C. The distorted orthorhombic perovskite structure can be indexed in the space group Pnma with lattice parameters a=5.4768 (1)Å, b=7.7450 (2)Å, and c=5.4574 (1)Å at room temperature, but undergoes a structural phase transition and enters into a P21/m monoclinic distorted perovskite phase below 150K with a=5.4173 (2), b=7.7286 (4) and c=5.4930 (3). The structural transition is coincident with the onset of magnetic interactions. At lower temperatures a weak ferromagnetic structure is evident related to antiferromagnetic Cr-spin canting and a spin-glass transition is observed at ≈40K. The semiconducting-type electrical resistivity is relatively low, associated with Cr3+/Cr4+ electron hopping, and shows considerable magneto-resistance (up to 15%). Due to the low resistivity the dielectric permittivity εr could be determined only below T<80K to be ≈300 and did not show any strong temperature-dependence. Ferroelectricity was not detected in the T-range investigated and no magnetocapacitance effects were observed.

Magnetic and Transport properties of Co-Cu Microwires

Abstract We report on the magnetic, transport and structural properties of Cox-Cu100-x (5≤x≤40) glass-coated microwires. For x=5 we observed the resistivity minimum at 40 K associated with the Kondo effect. For x ? 10 we observed considerable magnetoresistance effect. Temperature dependence of susceptibility show considerable difference for x&gt;10 and x≤ 10 attributed to the presence of small Co grains embedded in the Cu matrix for x? 10. Using X-ray diffraction we found, that the structure of Cox-Cu100-x microwires x ? 10 is granular consisting of two phases: fcc Cu appearing in all the samples and fcc α-Co presented only in microwires with higher Co content.

GMR effect in Co-Cu microwires

We studied magnetic properties and GMR effect of Cox − Cu100−x (10 ≤ x30 at%) microwires. We observed considerable magnetoresistance (MR), ΔR/R, in Co-Cu glass coated microwires with x = 10–30%. For low x content (x = 10), ΔR/R we observed negative MR, tending to saturate in high magnetic fields, H. On the other hand, for the samples x = 30 ΔR/R(H) dependences showed non-monotonic behavior, exhibiting ΔR/R increase with H at low H-values (up to 5 kOe) and also considerable GMR effect.

Kondo Effect and Magnetotransport Properties in Co-Cu Microwires

We studied magnetic, transport and structural properties of granular Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100-x</sub> glass-coated microwires. Co-Cu microwires exhibited considerable magnetoresistance (MR) effect. For x = 5% we observed the resistivity minimum at 40 K associated with the Kondo effect. For x >; 10 partial evidences of granular structure have been observed. Temperature dependence of magnetization measured in microwires Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100-x</sub> with x ≥ 10 during a cooling regime without external magnetic field (ZFC) and in the presence of the field (FC) show considerable difference at low temperatures, attributed by us with the presence of small Co grains embedded in the Cu matrix. By X-ray diffraction we found, that the structure of the metallic nucleus is granular consisting of two phases: fcc Cu appearing in all the samples and fcc α-Co presented only in microwires with higher Co content. For low Co content (x ≤ 10%) XRD magnetic and magneto-transport measurements indicate that Co atoms and small Co clusters are distributed within the Cu crystals.

Magnetic and transport properties of granular and Heusler-type glass-coated microwires

We studied magnetic and structural properties of granular CoxCu100−x (5<x<40at%), Cu63Fe37 and Heusler-type Ni2MnGa glass-coated microwires. We found that the structure of Co–Cu microwires consists of two phases: fcc Cu for all the samples and fcc α-Co present for higher Co content. In the case of low Co content, Co atoms are distributed within the Cu matrix. The quantity and the size of grains strongly depend on the geometry of the microwire. Co–Cu and Fe–Cu microwires exhibited considerable magnetoresistance (MR). For CoxCu100−x microwires at x≥30 the anisotropic contribution to MR has been observed. Temperature dependences of magnetization measured without an external magnetic field (ZFC) and in the presence of a field (FC) show considerable difference below 20K, indicating the presence of small α-Fe or Co grains embedded in the Cu matrix. Annealed Ni2MnGa microwires showed ferromagnetic behavior with Curie temperature about 330K and polycrystalline structure with space group I4/mmm and lattice parameters a=3.75Å and c=6.78Å.

Theoretical investigation on organic magnetoresistance based on Zeeman interaction

Based on the magnetic field-spin Zeeman interaction, a mechanism is suggested to explain the organic magnetoresistance (OMR). It is found that a considerable magnetoresistance (MR) could be obtained in organic semiconductors (OSCs). The value of MR is sensitive to the carrier concentration and the mobility (or the charge-transfer integral). We speculate that the MR in organic materials should be phonon dependent. This investigation is consistent with the present experimental observations on OMR.

Cu-doping induced ferromagnetic insulating behavior and domain wall pinning effects in LaMnO3

A systematic study on the structural, magnetic, and electrical transport properties was performed for the LaMn(subscript 1-x)Cu(subscript x)O3 system. A single phase of orthorhombic perovskite structure was formed for x=0.05-0.40. A striking paramagnetic-ferromagnetic transition and a considerable magnetoresistance effect were observed at the ferromagnetic ordering temperature T(subscript C), but no insulator-metal transition induced by Cu-doping was observed. Below T(subscript C), a visible unexpected drop was observed in the ac susceptibility and zero-field-cooled dc magnetization for the dilute doped samples with x≤0.10, which was proven to be associated with domain wall pinning effects by milling the bulk material into single domain particles. It is validated that there is no exchange interaction between Cu and Mn, and double exchange interactions between Mn(superscript 3+) and Mn(superscript 4+) are induced by Cu-doping in the anti-ferromagnetic LaMnO3 matrix, whereas the severe distortion and disorder caused by occupied-dopant prohibits charge carriers from hopping.

Electronic Transport and Magnetic Properties in Y$_{0.125}$Ca${\rm }_{0.875}$MnO$_{3}$ Manganite

A rare-earth-like manganite Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.125</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.875</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> was systemically studied by the structure, electric and magnetic measurement. The results show that there exists a considerable magnetoresistance effect in this system. And two transitions are found on electrical transport corresponding to conventional metal-insulator (M-I) transition and Kondo-like behavior. From the magnetization in the zero-field-cooled (ZFC) and field-cooled (FC), a large irreversibility was observed with a cusp at 108 K about considered as spin-glass freezing temperature. Below 108 K, a coexistence of ferromagnetic spin-glass and ferromagnetic ordering phase appears, which indicates a long-range ferromagnetic behavior in spin-glass state. These suggest an intrinsic ferromagnetic spin-glass state in the Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.125</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.875</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> system at low temperatures and may be suppressed with applied higher field of about 8.0 Tesla.

Magnetic Coupling in La&lt;sub&gt;0.7&lt;/sub&gt;Ca&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt;/YBa&lt;sub&gt;2&lt;/sub&gt;Cu&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;/La&lt;sub&gt;0.7&lt;/sub&gt;Ca&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Trilayers

We report on the interplay between ferromagnetism and superconductivity in trilayers La0.7Ca0.3MnO3/YBa2Cu3O7/La0.7Ca0.3MnO3 made of half metallic manganite and high temperature superconductor cuprate. Samples with a fully oxygenated cuprate show a magnetic field interval where the magnetizations of the manganite are aligned antiparallel. A considerable magnetoresistance accompanies the switching between magnetization configurations (parallel vs. antiparallel) of the manganite moments. Suppression of the free carrier density of the cuprate which occurs upon oxygen depletion, results in deep modifications in the shape of the normal state hysteresis loops indicating that there may be a magnetic coupling mediated by free carrier density of the cuprate. This result outlines the importance of quasiparticle transmission in the interplay between ferromagnetism and superconductivity in this kind of samples.

A magnetoresistance device based on a magnetic-barrier nanostructure

A magnetoresistance device is proposed in a two-dimensional electron gas modulated by a magnetic barrier, which can be realized experimentally by the deposition of two parallel ferromagnetic strips on the top and bottom of a GaAs heterostructure. A considerable magnetoresistance effect is found in this device, due to the significant difference between electronic transmissions through parallel and antiparallel magnetization configurations.

The conductance and magnetoresistance effect in a periodically magnetically modulated nanostructure

In this paper, we theoretically investigate the conductance and the magnetoresistance effect in a periodically magnetically modulated two-dimensional electron gas. It is shown that there exists a significant conductance difference for electrons through the parallel and antiparallel magnetization configurations, which leads to a considerable magnetoresistance effect. It is also shown that the conductance and the magnetoresistance effect depend on both the temperature and the number of the periodic magnetic barriers.

The magnetoresistance effect in a nanostructure with the periodic magnetic barriers

The magnetoresistance (MR) effect is theoretically investigated in a periodic magnetically modulated nanostructure, which can be realized experimentally by depositing periodic parallel ferromagnetic strips on the top of a heterostructure. We find that there exists a significant conductance difference for electrons through the parallel (P) and antiparallel (AP) magnetization configurations, which results in a considerable magnetoresistance effect. We also find that the magnetoresistance effect depends not only on the temperature but also on the number of the periodic magnetic barriers.

MAGNETORESISTANCE EFFECT IN A MAGNETIC–ELECTRIC-BARRIER STRUCTURE

A Magnetoresistance device is proposed in a both magnetically and electrically modulated two-dimensional electron gas, which can be realized experimentally by the deposition, on the top and bottom of a semiconductor heterostructure, of two parallel metallic ferromagnetic strips under an applied voltage. It is shown that a considerable magnetoresistance effect can be achieved in such a device due to the significant transmission difference for electrons through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio depends strongly on the applied voltage to the stripe in the device. These interesting properties may provide an alternative scheme to realize magnetoresistance effect in hybrid ferromagnetic and semiconductor systems, and this system may be used as a voltage-tunable magnetoresistance device.

Magnetoresistance effect in a hybrid ferromagnetic/semiconductor nanostructure

We propose a Magnetoresistance device in a magnetically modulated two-dimensional electron gas, which can be realized experimentally by the deposition of two parallel ferromagnetic strips on the top and bottom of a semiconductor heterostructure. It is shown that there exists a significant transmission difference for electrons through the parallel and antiparallel magnetization configurations of such a device, which leads to a considerable magnetoresistance effect. It is also shown that the magnetoresistance ratio of the device depends greatly on the magnetic strength difference in the two delta barriers of the system.

Magnetoresistance effect in a both magnetically and electrically modulated nanostructure

We propose a magnetoresistance device in a both magnetically and electrically modulated two-dimensional electron gas, which can be realized experimentally by the deposition, on the top and bottom of a semiconductor heterostructure, of two parallel metallic ferromagnetic strips under an applied voltage. It is shown that a considerable magnetoresistance effect can be achieved in such a device due to the significant transmission difference for electrons through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio depends strongly on the applied voltage to the stripe in the device. These interesting properties may provide an alternative scheme to realize magnetoresistance effect in hybrid ferromagnetic/semiconductor nanosystems, and this system may be used as a voltage-tunable magnetoresistance device.

Current-sensitive electroresistance and the response to a magnetic field in La0.8Ca0.2MnO3 epitaxial thin films

The influence of a transport dc current on the resistivity of La0.8Ca0.2MnO3 epitaxial thin films and their response to a magnetic field has been investigated. We found that when the applied dc current exceeds a threshold value, the electric resistivity in these films could be significantly enhanced. Such observations are completely repeatable. More attractive is that the enhanced resistance turns out to be sensitive to a weak current in a wide temperature range from 10 to 300 K. Even a very small dc current could remarkably depress the high resistance, showing a colossal electroresistance (ER) effect. ER reaches ∼1175% at temperatures lower than ∼50K, and ∼705% at 300 K for a current changing from 0.72 to 10.5 μA. A highly nonlinear behavior of the I–V curves persists even to room temperature. Significant influence of the magnetic field on the electric transports was also observed. It is found that a low field of 0.25 T could remarkably affect the I–V curves, resulting in a considerable magnetoresistance (MR).