Magnetic Resistivity Research Articles

2D versus 3D-Like Electrical Behavior of MXene Thin Films: Insights from Weak Localization in the Role of Thickness, Interflake Coupling and Defects.

MXenes stand out from other 2D materials because they combine very good electrical conductivity with hydrophilicity, allowing cost-effective processing as thin films. Therefore, there is a high fundamental interest in unraveling the electronic transport mechanisms at stake in multilayers of the most conducting MXene, Ti3C2Tx. Although weak localization (WL) has been proposed as the dominating low-temperature (LT) transport mechanism in Ti3C2Tx thin films, there have been few attempts to model it quantitatively. In this work, the role of important structural parameters - thickness, interflake coupling, defects - on the dimensionality of the LT transport mechanisms in spin-coated Ti3C2Tx thin films is investigated through LT and magnetic field dependent resistivity measurements. A dimensional crossover from 2D to 3D WL is clearly evidenced when the film thickness exceeds the dephasing length lϕ, estimated here in the 50-100 nm range. 2D WL can be restored by weakening the coupling between adjacent flakes, the intrinsic thickness of which is lower than lϕ, hence acting as parallel 2D conductors. Alternatively, lϕ can be reduced down to the 10 nm range by defects. These results clearly emphasize the ability of WL quantitative study to give deep insights in the physics of electron transport in MXene thinfilms.

Dust evolution during a protostellar collapse: Influence on the coupling between the neutral gas and magnetic field

Context. The extent of the coupling between the magnetic field and the gas during the collapsing phase of star-forming cores is strongly affected by the dust size distribution, which is expected to evolve by means of coagulation, fragmentation, and other collision outcomes. Aims. We aim to investigate the influence of key parameters on the evolution of the dust distribution, as well as on the magnetic resistivities during protostellar collapse. Methods. We performed a set of collapsing single-zone simulations with shark. The code computes the evolution of the dust distribution, accounting for different grain growth and destruction processes, with the grain collisions being driven by brownian motion, turbulence, and ambipolar drift. It also computes the charges carried by each grain species and the ion and electron densities, as well as the magnetic resistivities. Results. We find that the dust distribution significantly evolves during the protostellar collapse, shaping the magnetic resistivities. The peak size of the distribution, population of small grains, and, consequently, the magnetic resistivities are controlled by both coagulation and fragmentation rates. Under standard assumptions, the small grains coagulate very early as they collide by ambipolar drift, yielding magnetic resistivities that are many orders of magnitude apart from the non-evolving dust case. In particular, the ambipolar resistivity, ηAD, is very high prior to nH = 1010 cm−3. As a consequence, magnetic braking is expected to be ineffective. In this case, large size protoplanetary discs should result, which is inconsistent with recent observations. To alleviate this tension, we identified mechanisms that are capable of reducing the ambipolar resistivity during the ensuing protostellar collapse. Among them, electrostatic repulsion and grain-grain erosion feature as the most promising approaches. Conclusions. The evolution of the magnetic resistivities during the protostellar collapse and consequently the shape of the magnetic field in the early life of the protoplanetary disc strongly depends on the possibility to repopulate the small grains or to prevent their early coagulation. Therefore, it is crucial to better constrain the collision outcomes and the dust grain’s elastic properties, especially the grain’s surface energy based on both theoretical and experimental approaches.

Resistivity effect in the vicinity of a coronal magnetic null point

Introduction: We aim to examine how magnetic resistivity impacts the movement of magnetoacoustic waves near a magnetic null-point in the solar corona.Method: The resistive, nonlinear MHD simulations are solved by the PLUTO code in 2.5D for different amount of the resistivity.Results and Discussion: Propagation of magnetoacoustic waves in the vicinity of a magnetic null point has the potential to create current sheets with high current density excitation and plasmoid generation. During the entire duration of the simulation, it is discovered that plasma density became significant due to the plasmoid and also current density is high for high resistivity. It is depicted that high resistivity also leads to bigger plasmoids or magnetic islands in comparison to small resistivity.

Correction: Effect of Cu substitution on the structural, magnetic, and dc electrical resistivity response of Co0.5Mg0.5-xCuxFe2O4 nanoferrites

Correction: Effect of Cu substitution on the structural, magnetic, and dc electrical resistivity response of Co0.5Mg0.5-xCuxFe2O4 nanoferrites

Ab Initio Studies of Mechanical, Dynamical, and Thermodynamic Properties of Fe-Pt Alloys.

The density functional theory (DFT) framework in the generalized gradient approximation (GGA) was employed to study the mechanical, dynamical, and thermodynamic properties of the ordered bimetallic Fe-Pt alloys with stoichiometric structures Fe3Pt, FePt, and FePt3. These alloys exhibit remarkable magnetic properties, high coercivity, excellent chemical stability, high magnetization, and corrosion resistance, making them potential candidates for application in high-density magnetic storage devices, magnetic recording media, and spintronic devices. The calculations of elastic constants showed that all the considered Fe-Pt alloys satisfy the Born necessary conditions for mechanical stability. Calculations on macroscopic elastic moduli showed that Fe-Pt alloys are ductile and characterized by greater resistance to deformation and volume change under external shearing forces. Furthermore, Fe-Pt alloys exhibit significant anisotropy due to variations in elastic constants and deviation of the universal anisotropy index value from zero. The equiatomic FePt showed dynamical stability, while the others showed softening of soft modes along high symmetry lines in the Brillouin zone. Moreover, from the phonon densities of states, we observed that Fe atomic vibrations are dominant at higher frequencies in Fe-rich compositions, while Pt vibrations are prevalent in Pt-rich.

Delineation of Potential Gold Mineralization Zones in the Kushaka Schist Belt, Northcentral Nigeria, Using Geochemical, Ground Magnetic, Induced Polarization, and Electrical Resistivity Methods

Delineation of Potential Gold Mineralization Zones in the Kushaka Schist Belt, Northcentral Nigeria, Using Geochemical, Ground Magnetic, Induced Polarization, and Electrical Resistivity Methods

Ca substitution effects on structure transformation and physical properties of (Eu,Ca)FeAs2 co-doped with La and Co

In this study, Ca substitution and carrier doping effect on phase formation temperature and physical/superconducting properties of (Eu0.9-xCaxLa0.1)(Fe0.97Co0.03)As2 ((Eu,Ca)112, x = 0–0.4) compounds were investigated. The best synthesis condition for obtaining pure phases vary (850–900 °C) depending on the Ca substitution amount. Ca substitution in the EuFeAs2 structure induced a structural transformation from orthorhombic I2mm to monoclinic P21/m symmetry. Single crystals of EuFeAs2 and (Eu0.9La0.1)FeAs2 were grown and their crystal structures were determined. Density functional theory calculations confirmed the transformation and stability of the La-doped Eu112 crystal structure with Ca substitution. Compared with the parent compound EuFeAs2, the effective substitution of Ca reduced the lattice constants. The magnetic and transport properties of (Eu0.9-xCaxLa0.1)(Fe0.97Co0.03)As2 compounds were studied using the temperature and field dependence of the magnetization and electrical resistivity measurements. Ca substitution suppressed the magnetic ordering of Eu and gradually reduced the Néel temperature TNEu. As determined by the magnetization and electrical resistivity data, the onset of critical temperature (Tc) values increased with Ca substitution increment from 26 K to 32.2 K and 31 K–34.8 K, respectively. Ca substitution slightly increased the upper critical field values, while the coherence length ξ values were slightly decreased. The Ca substitution and sintering temperature dependence of superconductivity, upper critical fields, lower critical fields, and Eu-related magnetic transitions were extracted. The new series of Eu-containing iron-based superconductors with high Tc provides an interesting playground in this field.

Magnetic and resistivity imaging of a probable fault within the Precambrian crystalline rocks in Ogbomoso, Southwestern Nigeria

A linear structure which is interpreted to be a fault was identified within the Precambrian basement complex rocks of the Ogbomoso Southwest Sheet 222 geological map, southwest Nigeria. The ground magnetic and electrical resistivity methods were used to investigate the structure and determine its physical characteristics. Five (5) traverses with lengths varying from 700–800 m and trending approximately NW–SE were established perpendicularly to the suspected fault. Total magnetic field data were acquired at 10 m interval, corrected for diurnal variation and inverted into 2D magnetic models using the Geosoft Oasis montaj software package. Dipole-Dipole resistivity data were acquired along the traverses using a dipole length of 20 m with expansion factor n varying from 1 to 5 and modelled to generate 2D resistivity structures with the DIPPROTM software package. Thirty-seven (37) depth sounding datasets were acquired, quantitatively interpreted and the results used to generate geoelectric sections across the suspected geologic feature. Three major magnetic dyke lineaments D1, D2 and D3 (60 – 164 m wide and 70 – ∞ depth extent) characterised by peak negative (−44 to −81 nT) magnetic anomalies and equivalent resistivity lineaments R1, R2 and R3 (50 – 140 m wide and 40 to >60 m depth extent) typified by low resistivity (10 – 750 Ωm) vertical discontinuities were delineated. The northern edges of lineaments D2 and R2 coincide significantly with the spatial location of the suspected fault F1 – F1 while D1 and R1 and D3 and R3 correlated and are newly identified parallel faults F2 – F2 and F3 – F3 to F1 – F1 and probably syngenetic with it.

Concurrence of directional Kondo transport and incommensurate magnetic order in the layered material AgCrSe2

In this work, we report on the concurrent emergence of the directional Kondo behavior and incommensurate magnetic ordering in a layered material. We employ temperature- and magnetic field-dependent resistivity measurements, susceptibility measurements, and high resolution wavelength X-ray diffraction spectroscopy to study the electronic properties of AgCrSe2. Impurity Kondo behavior with a characteristic temperature of TK = 32 K is identified through quantitative analysis of the in-plane resistivity, substantiated by magneto-transport measurements. The excellent agreement between our experimental data and the Schlottmann’s scaling theory allows us to determine the impurity spin as S = 3/2. Furthermore, we discuss the origin of the Kondo behavior and its relation to the material’s antiferromagnetic transition. Our study uncovers a rare phenomenon—the equivalence of the Néel temperature and the Kondo temperature—paving the way for further investigations into the intricate interplay between impurity physics and magnetic phenomena in quantum materials, with potential applications in advanced electronic and magnetic devices.

Structural and electronic transport properties of Zn- and Ga-doped Bi2− x Sb x Te3− y Se y topological insulator single crystals

A comprehensive study of structural and magnetotransport properties of pristine Bi2−x Sb x Te3−y Se y (BSTS) single crystals and doped with Zn (BSTS:Zn) and Ga (BSTS:Ga) are presented here. Magnetic field dependent Hall resistivities of the single crystals indicate that the holes are the majority carriers. The field dependent resistivity curves at different temperatures of the crystals display cusp-like characteristics at low magnetic fields, attributed to two-dimensional (2D) weak antilocalization (WAL) effect. We fit the observed low-field WAL effects at low temperatures using 2D and three-dimensional (3D) Hikami-Larkin-Nagaoka (HLN) equations. The 2D HLN equation fits the data more closely than the 3D HLN equation, indicating a 2D nature. The 2D HLN equation fit to the low field WAL effects at various temperatures reveal a phase coherence length (l φ) that decreases as temperature increases. The variation of l φ with temperature follows T −0.41 power law for BSTS:Zn, suggesting that the dominant dephasing mechanism is a 2D electron–electron (e−e) interactions. For pristine BSTS and BSTS:Ga, l φ(T) is described by considering a coexistence of 2D e−e and electron–phonon (e−p) interactions in the single crystals. The temperature variation of the longitudinal resistance in BSTS:Ga is described by 3D Mott variable range hoping model. In contrast, the transport mechanisms of both pristine BSTS and BSTS:Zn are described by a combination of 2D WAL/EEI models and 3D WAL.

Effect of rare earth (Sm3+) substitution in mixed Ni-Zn-Co ferrites: Structural, magnetic, and DC electrical resistivity studies

NiZnCo ferrite has good magnetic properties and is one of the core materials used in magnetic devices. The solid-state reaction approach is utilized to synthesize Ni0.4Zn0.35Co0.25Fe2-xSmxO4 (x = 0.0, 0.02, 0.04, 0.06, 0.08, and 0.1) ferrites for investigation of structural, morphological, functional, magnetic and electrical resistivity properties using various characterization techniques. The techniques used for characterization were XRD, SEM, FTIR, VSM, and DC electrical resistivity. XRD spectra were used to determine phase confirmation, cubic crystallite size, andtheir variation with dopant content. No additional phase or impurity was found. The SEM pictures revealed ahomogeneous spherical particle formation with minimal porosity. With absorption bands under 1000 cm−1, FTIR spectra indicate the formation of a spinel structure. Tetrahedral (580 to 599 cm−1) and octahedral (388 to 399 cm−1) bond changes can be seen in infrared spectra. The magnetic hysteresis curves revealed soft ferromagnetic behavior, with coercivity (Oe) (532.13 to 312.10Oe) rising and saturation magnetization (Ms) (83.51 to 60.75 emu/g) falling as doping concentration increased. The DC electrical resistivity of synthesized nanoparticles with various compositions was measured against higher temperatures to confirm their semiconductor nature. The findings demonstrated the typical decreasing trend with rising temperature.

A correlated ferromagnetic polar metal by design.

Polar metals have recently garnered increasing interest because of their promising functionalities. Here we report the experimental realization of an intrinsic coexisting ferromagnetism, polar distortion and metallicity in quasi-two-dimensional Ca3Co3O8. This material crystallizes with alternating stacking of oxygen tetrahedral CoO4 monolayers and octahedral CoO6 bilayers. The ferromagnetic metallic state is confined within the quasi-two-dimensional CoO6 layers, and the broken inversion symmetry arises simultaneously from the Co displacements. The breaking of both spatial-inversion and time-reversal symmetries, along with their strong coupling, gives rise to an intrinsic magnetochiral anisotropy with exotic magnetic field-free non-reciprocal electrical resistivity. An extraordinarily robust topological Hall effect persists over a broad temperature-magnetic field phase space, arising from dipole-induced Rashba spin-orbit coupling. Our work not only provides a rich platform to explore the coupling between polarity and magnetism in a metallic system, with extensive potential applications, but also defines a novel design strategy to access exotic correlated electronic states.

Investigation on the crystal structure, magnetic, and electrical transport properties of magnetron sputtered Co2FeGe Heusler alloy films

Crystal structure, magnetic, and electrical resistivity behaviour of Co2FeGe Heusler alloy films deposited at different sputtering parameters have been studied using X-ray diffraction, VSM, and standard four-probe techniques. Though the expected structure was L21, X-ray diffraction studies indicate the A 2-type disordered structure. All films exhibited soft ferromagnetic characteristics having a coercive field of 5-65 Oe and a high ferromagnetic ordering temperature (More than 700 K). The electrical resistivity of the films deposited on the Si substrates was influenced by the substrate temperatures. Out of the different scattering mechanisms present in the low and high-temperature regimes, the two-magnon scattering effect is dominant in all the films. The scattering mechanisms are the same in all films irrespective of the substrate temperature. The optimum sputter deposition parameters that yields good quality Co2FeGe Heusler alloy thin films were found to be 50 W power, 5 mTorr pressure, and 400 °C substrate temperature.

Study on Acoustic–Electric Response Characteristics of Unsaturated Loess under Different Moisture Content

In order to study the characteristics of P-wave velocity and resistivity of loess with different moisture contents, low-field nuclear magnetic resonance, resistivity, and P-wave velocity tests were carried out on loess samples with 11 different moisture contents. The test results show that under the condition of the same dry density, the water in loess exists in two forms: bound water and free water. With the increase in moisture content, the water porosity of loess increases, the proportion of free water increases, and the resistivity gradually decreases and then tends to be stable, showing a power function relationship with moisture content. When the moisture content is less than 20%, the P-wave velocity decreases with the increase in the moisture content. In comparison, when the moisture content is greater than 20%, the wave velocity increases with the increase in the moisture content. A modified relation between wave velocity and moisture content and saturation is put forward, and the relationship expression between wave velocity and resistivity of loess is established. Finally, the reliability is verified by experimental data. The research results have a certain guiding significance for real-time monitoring of loess moisture content and engineering stability analysis in the loess area.

Physical characterization, magnetic interactions and DC electrical resistivity properties of La3+ substituted NiZnCd nano ferrites

In this article, we substituted La3+ ions to explore the structural, magnetic, and DC electrical resistivity properties of Ni0.5Zn0.4Cd0.1Fe2-xLaxO4 (x = 0.0, 0.02, 0.04, 0.06, and 0.08) nano-structured spinel ferrites. We employed X-ray diffraction (XRD), Field-emission scanning electron microscopy (FESEM) with Energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), Vibrating sample magnetometry (VSM), and electrical measurements to characterize the studied samples, which were synthesized using the sol–gel auto-combustion process. XRD analysis confirmed that the prepared materials formed a single-phase nanostructure. Using Debye-Scherer's formula, we calculated the average crystallite size, which ranged from 29.01 to 21.52 nm. FESEM images demonstrated that each sample exhibited spherical nanocrystalline behavior. The variations of the prepared samples were confirmed constitutionally by EDX. The FTIR data revealed two absorption bands for all synthesized materials at υ1 = 562.18 to 590.51 cm−1 and υ2 = 410.18 to 430.51 cm−1, corresponding to the tetrahedral and octahedral sites of the spinel structure, respectively. Vibrant sample magnetometry spectra were utilized to investigate how La3+-doping affects the magnetic characteristics of NiZnCd ferrite. Due to enhanced La3+-doping, saturation magnetization, and coercivity values decreased. The La3+ doping of NiZnCd nano ferrites resulted in changes in saturation magnetization (from 83.66 to 69.57 emu/g), coercivity (from 33.75 to 60.51 Oe), and remanence magnetization (from 29.62 to 33.12 emu/g). These variations suggest the potential utility of the samples for magnetic recording and memory applications. The semiconducting behavior has been confirmed by the DC electrical resistivity measured values using a two-probe method. Data on DC electrical resistivity were also utilized to determine carrier concentration and activation energy, establishing a connection with La3+ replacement.

Cationic disorder: Governing the spin-insulatronic properties of nanocrystalline ZnFe2O4 thin films

Controlling cation order/disorder in spinel offers a highly effective means of tailoring material properties by modifying inter- and intra-sub-lattice ionic interactions. In this study, we conducted high-temperature magnetization measurements (300–1000 K) to determine average Curie temperatures (TC) for nanocrystalline ZnFe2O4 thin films. Thermodynamical stability of these films under extreme conditions was investigated by assessing lattice structures, oxygen vacancies, magnetization, and electric resistivity for spin-insulatronic applications. Reversible cation inversion via heat treatments (in-situ and ex-situ) yields tunable ferrimagnetic (FiM) order in ZnFe2O4, with TC ranging from 425 to 710 K. First-principles calculations highlight effective cation inversion mitigating magnetic frustration, promoting collinear FiM ordering, and elevating TC. Oxygen vacancies further reinforce ferrimagnetism, slightly reducing resistivity through the formation of Fe-3d gap states near the Fermi level. A proposed magnetic nanophase diagram elucidates dominant competing magnetic ground states (cluster spin-glassy state, FiM, and antiferromagnetic) with increasing growth temperature, fostering innovative homo-architectures from multiple ZnFe2O4 thin films with diverse functionalities.

Numerical MHD simulations of solar flares and their associated small-scale structures

ABSTRACT Using numerical simulations, we study the formation and dynamics of solar flares in a local region of the solar atmosphere. The magnetohydrodynamics (MHD) equations describe the dynamic evolution of flares, including space-dependent and anomalous magnetic resistivity and highly anisotropic thermal conduction on a 2.5 D slice. We adopt an initial solar atmospheric model in magnetohydrostatic equilibrium, with a magnetic configuration consisting of a vertical current sheet, which helps trigger the magnetic reconnection process. Specifically, we study three scenarios, two with only resistivity and the third with resistivity plus thermal conduction. The main results of the numerical simulations show differences in the global morphology of the flares, including the post-flare loops and the current sheet in three cases. In particular, localized resistivity produces more substructure around the post-flare loops that could be related to the Ritchmyer–Meshkov Instability (RMI). Furthermore, in the scenario of anomalous resistivity, we identify the formation of a plasmoid and a jet at coronal heights. On the other hand, in the scenario with resistivity plus thermal conduction, the post-flare loops are smooth, and no apparent substructures develop. Besides, in the z-component of the current density for the Res + TC case, we observe the development of multiple magnetic islands generated due to the Tearing instability in the non-linear regime.

Structural investigation, magnetic and DC electrical resistivity properties of Co0.5-xNixZn0.5Fe2O4 nano ferrites

The Ni2+ substituted Cobalt-Zinc nano ferrites, designated as Co0.5-xNixZn0.5Fe2O4 with x values ranging from 0.0 to 0.5, were synthesized using the sol–gel auto-combustion method. Various characterization techniques, including x-ray diffraction (XRD), field-effect scanning electron microscopy (FESEM), Fourier Transform Infrared (FTIR) spectroscopy, vibrating sample magnetometer (VSM), and DC electrical resistivity measurements, were employed to analyze the prepared samples. XRD analysis revealed a cubic spinel structure with a lattice constant ranging from 8.384 to 8.412 Å. FESEM examination indicated non-uniform-shaped spherical grains in the nanometer range for the synthesized samples. The FTIR spectra of the spinel ferrites revealed two distinctive bands, ν2 (580–592 cm−1) and ν1 (390–412 cm−1), which are the characteristics of spinel-structured ferrite nanomaterials. With progressive substitution (x varying from 0.0 to 0.5), the saturation magnetization (Ms) values exhibited a gradual decrease, starting from Ms = 60.97 emu/g (at x = 0.0) and reaching Ms = 38.79 emu/g (at x = 0.5). A discernible pattern was observed in coercivity (Hc), which rose from Hc = 115 Oe (at x = 0.0) to Hc = 920 Oe (at x = 0.5), with peak values determined through VSM analysis. Similar to semiconductors, the electrical resistivity experienced a decline with increasing temperature, indicative of a negative temperature coefficient.

Extremely large magnetoresistance and quantum oscillations in semimetal Ni3In2S2

In this work, we present magnetotransport properties and quantum oscillations in single-crystalline shandite compound Ni3In2S2, which is a recently identified semimetal with endless Dirac-nodal lines. Ni3In2S2 displays a giant transverse magnetoresistance of ∼24 000 % at 2 K and 14 T and a magnetic field-induced resistivity upturn behavior at low temperatures. Below 50 K, the magnetoresistance curves show a linear magnetic field dependence under high magnetic fields. The computation results indicate that Ni3In2S2 is a semimetal with linear crossings near the Fermi level. The small effective mass, deduced from de Haas–van Alphen quantum oscillations, suggests the high carrier mobility in Ni3In2S2. The high mobility and quantum linear magnetoresistance resulting from the linear dispersive bands jointly lead to the extreme transverse magnetoresistance in our Ni3In2S2 crystal. Our findings can be a reference to understand and search for semimetals with extreme magnetoresistance.

Anisotropic magneto-resistivity and magnetocaloric effect in DyAl2

In this study, we experimentally and theoretically investigate the correlation between the anisotropic magnetic resistivity and magnetocaloric effect in DyAl2 single crystals. DyAl2 crystallizes in the C15 Laves phase structure with cubic symmetry. While some earlier studies revealed that the isothermal entropy change in dialuminides follows a similar trend as the electrical resistivity change as a function of temperature and magnetic field, the correlation between anisotropic behavior of these two physical parameters is yet to be explored to the best of our knowledge. To address this gap, we measured electrical resistivity of DyAl2 single crystals along two different directions in zero and applied magnetic fields and compared the experimental results with our theoretical model. For the theoretical analysis, we employed a model Hamiltonian in the mean-field approximation, considering the exchange interaction, Zeeman effect, and crystalline electric field associated with the cubic symmetry. Our findings reveal a significant dependence of DyAl2 resistivity on the direction of the applied magnetic field, in agreement with our theoretical results. These outcomes emphasize the interplay between magnetocaloric effect and magneto-resistivity, underscoring the potential of the magnetocaloric effect as a valuable tool for gaining deeper insights into basic physical properties including electron transport behavior.