Anomalous Hall Effect Coefficient Research Articles

Sign change of anomalous Hall effect with temperature in Cr2.63V0.25Te4 single crystal

Anomalous Hall effect, an interesting transport behavior, is of importance topic for fundamental physics and device application. Recently, the sign change of anomalous Hall effect (AHE) in some materials has being concerned. Here, we study the electrical transport, magnetic properties, and AHE of Cr2.63V0.25Te4 single crystals. Cr2.63V0.25Te4 shows a bad metal behavior with a resistivity kink at 178 K, corresponding to a peak on a heat capacity–temperature curve, and the strong electron correlation should be a dominant transport mechanism below 178 K. At this temperature, the magnetization shows a sharp magnetic transition. The linear Hall resistivity at a high field with a positive slope suggests a p-type conductivity for bulk Cr2.63V0.25Te4. The clear AHE is observed below 180 K with a larger anomalous Hall conductivity σxy ∼ 2000 Ω−1 cm−1 at 3 K. For 3–60 K, an AHE coefficient Rs is negative, and Rs is positive between 100 and 180 K. The sign change of AHE may be due to Fermi level crossing the overlap of 3d band in ferromagnetic transition-metal materials. Based on our analysis, the AHE mechanism should be the skew scattering. Our results reveal the interesting physical properties in Cr2.63V0.25Te4 single crystals and give another system to study AHE for future Hall device design.

Magnetic and magnetotransport properties of MnSb polycrystals near equatomic composition

In this work, we studied properties of the MnSb polycrystalline samples synthesized from a melt of high-purity elements. We observed the presence of a ferromagnetic state with Curie temperature significantly higher than room temperature (Tc≈568 K). The results of structural and magnetic studies suggest the presence of a slight deviation from the equatomic composition towards the small excess of Mn (∼ 1 at.%). It was found that the studied sample have high resistivity (up to 425 μΩ⋅cm) at room temperature, however, it significantly decreases upon cooling, breaking the Mooij correlation. The magnetoresistance of the MnSb polycrystal is positive at low temperatures and does not get saturated in studied magnetic field range (≤40 kOe), which suggests that this contribution stems from the classical Lorenz mechanism. Negative magnetoresistance contribution, associated with the suppression of thermal spin fluctuations by external magnetic field, becomes dominant at higher temperatures (T≥74 K). The normal Hall effect coefficient is positive and significantly increases upon heating, which indicates a substantial variation of delocalized holes density with temperature. The anomalous Hall effect coefficient is also positive, and its temperature dependence suggests that the skew scattering mechanism provides a considerable contribution at low temperatures.

Anomalous Hall effect and ordinary Hall effect in variable range hopping regime of inhomogeneous ferromagnetic semiconductor

Anomalous Hall effect (AHE) and ordinary Hall effect (OHE) in variable range hopping regime of ferromagnetic semiconductor are important for understanding the localized impurity states at different energy levels within the band gap, and provides insight into the specific percolation networks of the thermally excited spin-polarized carriers. Here we report the experiments of both OHE and AHE in Mott and Efros variable range hopping regimes of inhomogeneous In0.27Co0.73O1-v ferromagnetic semiconductor films with the tunable localized electron density and localization length. We found an unusual scaling relation between the AHE coefficient RAH and the longitudinal resistivity ρxx, RAH∝ρxxβ with β>2 , which contrasts the scaling relation of OHE coefficient ROH∝ρxxα with α<1. More strikingly, the sign of AHE coefficient reverses with decreasing temperature for specific electron density. We argue that these surprising results are related to the specific impurity energy band structure of the oxygen vacancies within the band gap of inhomogeneous In0.27Co0.73O1-v ferromagnetic semiconductor films.

Correlation between antisymmetric magnetoresistance and anomalous hall effect in Co1− x Tb x films

The antisymmetric magnetoresistance (MR) and anomalous Hall effect (AHE) of perpendicularly magnetized Co1−x Tb x thin films with different Tb concentration have been investigated under gradient magnetic fields. Owing to the presence of tilting domain walls, the Co1−x Tb x films exhibit anomalous antisymmetric MR, whose polarity reversal is strongly dependent on the film composition and exactly consistent with the simultaneously measured AHE. Our results suggest that the effect of disorder scattering from impurities and dispersive domain wall boundaries is more pronounced in Co1−x Tb x alloy films distant from the compensation point. Moreover, the modulation of AHE coefficient Rs directly leads to the remarkable variation of antisymmetric MR, providing a new insight into design of domain wall based electronic devices.

Spin gapless semiconducting behavior in inverse Heusler Mn2-xCo1+xAl (0[formula omitted]x[formula omitted]1.75) thin films

We correlate the structural, electrical, and magnetotransport properties of co-sputtered Mn2-xCo1+xAl full Heusler alloy thin films (0≤x≤1.75) in terms of Co/Mn concentration variation concerning the spin gapless semiconducting (SGS) behavior. The alloy thin films are found to stabilize in B2 order for near stoichiometric films, i.e. (x = 0 and x = 1), with the gradual change in the ordering and lattice parameter through Mn concentration variation. Magnetization measurements in Mn2-xCo1+xAl thin films reveal the ferromagnetic and ferrimagnetic character for x = 1.75, 1.5, 1.25 & 1, and x = 0, 0.5 & 0.75, respectively. The longitudinal resistivity measurement revealed that the films exhibit semiconducting behavior with a change in sign of the temperature coefficient of resistance with temperature. The anomalous Hall conductivity values for the Mn2-xCo1+xAl thin films are extracted from the Anomalous Hall effect (AHE) measurements. The non-saturating positive MR (linear in H) is being reported for the first time in the Mn2CoAl thin films. The value of the AHE coefficient and positive MR together serve as a piece of experimental evidence for the SGS character in the thin film. The SGS behavior becomes predominant at higher Mn concentration. Highly resistive thin films with ferromagnetic (ferrimagnetic) character in Co2MnAl (Mn2CoAl) could be beneficial for semiconductor spintronics, where we need a good resistive element to match up with Silicon base substrate.

Magnetic field direction dependence of topological Hall effect like features in synthetic ferromagnetic and antiferromagnetic multilayers

The anomalies in the transverse resistivity are usually thought to be Topological Hall Effects (THEs), which have been considered as the trait of topologically nontrivial spin textures, such as the skyrmion phase. However, the origin of the THE-like features is still under debate. Here, we present the observation of THE-like features in synthetic antiferromagnetic [Pd/Co]/Ru/[Co/Pd] and synthetic ferromagnetic [Pd/Co]/NiO/[Co/Pd] structures. The Pd-rich alloys, which are formed due to the heterogeneous component and the gradual intermixing at the Co/Pd interface, result in a negative anomalous Hall effect coefficient, causing the peak and dip features in transport measurements. By changing the external magnetic field from out-of-plane to in-plane, the magnitude and width of the bump feature in THE curves can be modified, which is caused by the different anisotropy energy of the components in the heterogeneous ferromagnets. The present work broadens the perception of THE-like features and may add a different dimension to understand the magnetization reversal in magnetic multilayers.

Experimental observation of anomalies in the electrical, magnetic, and galvanomagnetic properties of cobalt-based Heusler alloys with varying transition elements

The residual resistivity, Hall effect, and magnetization of Co2YSi (Y = Ti, V, Cr, Mn, Fe, Co, Ni) Heusler alloys were considered at T = 4.2 K and in fields up to 100 kOe. It is shown that as the number of valence electrons z ranges from 26 to 32, significant changes in the residual resistivity ρ0, magnetization Ms, sign and magnitude of the normal R0 and anomalous RS Hall effect coefficients are observed during the transition from Co2TiSi to Co2NiSi. It is established that there is a clear correlation between the values ρ0, R0, RS and Ms, depending on the number z, which can be associated with the appearance of a half-metal ferromagnetic state and/or spin gapless semiconductor. As z changes, the anomalous Hall effect coefficient has a power-law dependence on the residual electrical resistivity with an exponent of k = 3.1, which diverges with existing theories but agrees well with the experimental data obtained earlier for similar half-metallic ferromagnetic Heusler alloys.

Anomalous Hall effect in two-dimensional non-collinear antiferromagnetic semiconductor Cr0.68Se

Cr0.68Se single crystals with two-dimensional (2D) character have been grown, and the detailed magnetization M(T), electrical transport properties (including longitudinal resistivity ρxx and Hall resistivity ρxy), and thermal transport properties [including heat capacity Cp(T) and thermoelectric power S(T)] have been measured. There are some interesting phenomena: (i) Cr0.68Se presents a non-collinear antiferromagnetic (AFM) semiconducting behavior at the Néel temperature of TN = 42 K and with the activated energy of Eg = 3.9 meV; (ii) it exhibits the anomalous Hall effect (AHE) below TN and large negative magnetoresistance about 83.7% (2 K, 8.5 T). The AHE coefficient RS is 0.385 cm−3/C at T = 2 K, and the AHE conductivity σH is about 1 Ω−1 cm−1 at T = 40 K; (iii) the scaling behavior between the anomalous Hall resistivity ρxyA and the longitudinal resistivity ρxx is linear, and further analysis implies that the origin of the AHE in Cr0.68Se is dominated by the skew-scattering mechanism. Our results may be helpful for exploring the potential application of these kinds of 2D AFM semiconductors.

Testing dependence of anomalous Hall effect on resistivity inSrRuO3by its increase with electron irradiation

We measure the anomalous Hall effect (AHE) in several patterns of the itinerant ferromagnet ${\text{SrRuO}}_{3}$ before and after the patterns are irradiated with electrons. The irradiation increases the resistivity of the patterns due to the introduction of point defects and we find that the AHE coefficient ${R}_{s}$ scales with the total resistivity before and after irradiation which indicates that the AHE is determined by the total resistivity. We discuss possible origins of slight deviations from scaling that are observed at low temperature, particularly below 70 K.

Anomalous Hall effect in (Co41Fe39B20) x (Al-O)100 − x nanocomposites

The concentration dependence of the coefficient Rs characterizing the anomalous Hall effect (AHE) has been studied by measuring the electrical resistivity ρ, magnetoresistance, and the magnetic field dependence of magnetization and Hall resistivity of (Co41Fe39B20)x(Al-O)100 − x nanocomposite thin films. It has been demonstrated that the AHE coefficient increases by more than an order of magnitude with a decrease in the percentage x of the amorphous ferromagnetic metal from 60 to 30 and its behavior is described by the relation Rs ∼ ρm, where m = 0.46 ± 0.1. At the same time, the coefficient characterizing the normal Hall effect grows by a factor of less than 10. The mechanisms underlying the giant Hall effect in nanocomposites have been discussed.

Magnetotransport properties of Fe48Mn24Ga28Heusler alloys

Magnetotransport properties of an Fe${}_{48}$Mn${}_{24}$Ga${}_{28}$ Heusler-based ferromagnetic shape memory alloy are tracked in a temperature interval that covers both martensitic and austenitic phases. A large temperature hysteresis indicative of a coupled magnetostructural transition from ferromagnetic martensite to paramagnetic austenite is observed on the temperature dependencies of magnetization and electrical resistivity. The temperature dependency of the anomalous Hall-effect coefficient in Fe${}_{48}$Mn${}_{24}$Ga${}_{28}$ cannot be described in terms of skew scattering, side-jump, and intrinsic mechanisms of the anomalous Hall-effect theory. The Hall-effect resistivity in the martensitic state is smaller, but is of the same order of magnitude as in the case of the giant Hall effect in a half-metallic Co${}_{2}$MnAl. Specific features of the temperature dependencies of magnetization, resistivity, magnetoresistance, and ordinary and anomalous Hall-effect coefficients are discussed and the possible routes for increasing Hall-effect resistivity are suggested.

The anomalous Hall effect in the perpendicular Ta/CoFeB/MgO thin films

The anomalous Hall effect (AHE) in the perpendicular Ta/CoFeB/MgO thin film has been investigated. Between the AHE coefficient (RS) and longitudinal resistivity (ρxx), a linear behavior of RS/ρxx versus ρxx can be found. Moreover, the conductivity of the film is about 5 × 103 S/cm, which suggests that AHE in the Ta/CoFeB/MgO film be dominated by the intrinsic or scattering-independent mechanism.

Negative magnetoresistance and anomalous Hall effect in GeMnTe-SnMnTe spin-glass-like system

Magnetotransport properties of spin-glass-like Ge1−x−ySnxMnyTe mixed crystals with chemical composition changing in the range of 0.083≤x≤0.142 and 0.012≤y≤0.119 are presented. The observed negative magnetoresistance we attribute to two mechanisms, i.e., weak localization occurring at low fields and spin disorder scattering giving contribution mainly at higher magnetic fields. A pronounced hysteretic anomalous Hall effect (AHE) was observed. The estimated AHE coefficient shows a small temperature dependence and is dependent on Mn-content, with changes in the range of 10−7&amp;lt;RS&amp;lt;10−6m3/C. The scaling law analysis has proven that the AHE in this system is due to the extrinsic mechanisms, mainly due to the skew scattering accompanied with the side jump processes.

Determination of the normal and anomalous hall effect coefficients in ferromagnetic Ni50Mn35In15 − x Si x Heusler alloys at the martensitic transformation

The magnetization, the electrical resistivity, the magnetoresistance, and the Hall resistivity of Ni50Mn35In15 − xSix (x = 1.0, 3.0, 4.0) Heusler alloys are studied at T = 80-320 K. The martensitic transformation in these alloys occurs at T = 220–280 K from the high-temperature ferromagnetic austenite phase into the low-temperature martensite phase having a substantially lower magnetization. A method is proposed to determine the normal and anomalous Hall effect coefficients in the presence of magnetoresistance and a possible magnetization dependence of these coefficients. The resistivity of the alloys increases jumpwise during the martensitic transformation, reaches 150–200 μΩ cm, and is almost temperature-independent. The normal Hall effect coefficient is negative, is higher than that of nickel by an order of magnitude at T = 80 K, decreases monotonically with increasing temperature, approaches zero in austenite, and does not undergo sharp changes in the vicinity of the martensitic transformation. At x = 3, a normal Hall effect nonlinear in magnetization is detected in the immediate vicinity of the martensitic transformation. The temperature dependences of the anomalous Hall effect coefficient in both martensite and austenite and, especially, in the vicinity of the martensitic transformation cannot be described in terms of the skew scattering, the side jump, and the Karplus-Lutinger mechanisms from the anomalous Hall effect theory. The possible causes of this behavior of the magnetotransport properties in Heusler alloys are discussed.

Scaling of the paramagnetic anomalous Hall effect in SrRuO3

We extract the paramagnetic anomalous Hall effect (AHE) resistivity ${\ensuremath{\rho}}_{xy}^{\mathrm{AHE}}$ in thin films of the itinerant ferromagnet SrRuO${}_{3}$ and show that the AHE coefficient ${R}_{s}$ scales with the longitudinal resistivity ${\ensuremath{\rho}}_{xx}$. We fit the resistivity dependence of ${\ensuremath{\rho}}_{xy}^{\mathrm{AHE}}$ assuming two mechanisms: side jumps and Karplus-Luttinger (Berry phase) mechanism. For the latter, we consider the effect of a finite scattering time with a fractional power-law relation to ${\ensuremath{\rho}}_{xx}$.

Scaling of the anomalous Hall effect in SrRuO3

We measure the anomalous Hall effect (AHE) resistivity $\rho_{xy}$ in thin films of the itinerant ferromagnet SrRuO$_{3}$. At low temperatures, the AHE coefficient $R_{s}$ varies with $\rho_{xx}^2$, and at higher temperatures, $R_{s}$ reaches a peak and then changes sign just below $T_{c}$. We find that for all films studied $R_{s}$ scales with resistivity in the entire ferromagnetic phase. We attribute the observed behavior to the contribution of the extrinsic side jumps mechanism and the intrinsic Karplus-Luttinger (Berry phase) mechanism including the effect of finite scattering rates.

Anomalous Hall effect and magnetoresistance in the layered ferromagnetFe1∕4TaS2: The inelastic regime

The large magnetic anisotropy in the layered ferromagnet ${\mathrm{Fe}}_{1∕4}\mathrm{Ta}{\mathrm{S}}_{2}$ leads to very sharp reversals of the magnetization $\mathbf{M}$ at the coercive field. We have exploited this feature to measure the anomalous Hall effect (AHE), focusing on the AHE conductivity ${\ensuremath{\sigma}}_{xy}^{A}$ in the inelastic regime. At low temperature $T$ $(5--50\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, ${\ensuremath{\sigma}}_{xy}^{A}$ is $T$ independent, consistent with the Berry-phase/Karplus-Luttinger theory. Above $50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, we extract an inelastic AHE conductivity ${\ensuremath{\sigma}}_{xy}^{\mathit{in}}$ that scales as the square of $\ensuremath{\Delta}\ensuremath{\rho}$ (the $T$ dependent part of the resistivity $\ensuremath{\rho}$). The term ${\ensuremath{\sigma}}_{xy}^{\mathit{in}}$ clarifies the $T$ dependence and sign reversal of the AHE coefficient ${R}_{s}(T)$. We discuss the possible ubiquity of ${\ensuremath{\sigma}}_{xy}^{\mathit{in}}$ in ferromagnets and ideas for interpreting its scaling with ${(\ensuremath{\Delta}\ensuremath{\rho})}^{2}$. Measurements of the magnetoresistance (MR) reveal a rich pattern of behavior vs $T$ and field-tilt angle. We show that the two mechanisms, the anisotropic MR effect and field suppression of magnons, account for the intricate MR behavior, including the bow-tie features caused by the sharp reversals in $\mathbf{M}$.

Effect of heat treatment on transport and magnetic properties of Co-based amorphous alloys

Magnetotransport and magnetic properties of Co66Fe4B15Si15 amorphous ribbons, annealed in vacuum and in open air for various times, are studied. The air-annealed samples exhibit the presence of the near-surface hard magnetic layer. The anomalous Hall effect coefficient and the resistivity change simultaneously under heat treatment with slightly non-linear correlation between them. Positive magnetoresistance in low fields changes to negative magnetoresistance with increase of magnetic field. We explain both positive and negative magnetoresistance in terms of spin-dependent scattering.

Temperature dependent anomalous Hall effect in La–Ca–Mn–O films

The colossal magnetoresistance of La1−xCaxMnO3 has been reported in many experiments. We present our study of the anomalous Hall effect in epitaxial La0.67Ca0.33MnO3 thin films. We have measured the temperature dependence of resistivity, magnetization, and anomalous Hall effect coefficients between 300 and 5 K for our samples grown on different substrates. From these studies, the relation between the resistivity and anomalous Hall effect coefficient as well as the temperature dependence of the anomalous Hall effect coefficient are explored. Our results show that the direction of the anomalous Hall effect is reversed below approximately 100 K. This sign reversal is discussed in terms of band structure and the coexistence of hole-like and electron-like conduction.

Features of magnetic and kinetic properties of atomic-disordered solid γ-Mn 3Ga solutions in the antiferromagnetic spin glass state

Magnetic properties, the Hall effect and crystallic structure of atomic-disordered γ-MnGa near the stoichiometric γ-Mn 3Ga composition were studied within the temperatures 300–1000 K. Heisenberg spin glass with random competing anisotropy have been obtained where the longitudinal L, transverse T and mixed LT-phases of spin glass, the Q-phase with nonzero parameter of order have been experimentally observed. Successive transitions in spin glass phase have been found. The anomalous Hall effect coefficient is temperature independent and equals R a=0.8×10 −9 Ω cm G −1 both in the paramagnetic region and in the spin glass state.