Magnetic Transport Properties Research Articles

Observation of Giant Topological Hall Effect in Room-Temperature Ferromagnet Cr0.82Te

Abstract Novel magnetic materials with non-trivial magnetic structures have led to exotic magnetic transport properties and significantly promoted the development of spintronics in recent years. Among them is the Cr x Te y family, the magnetism of which can persist above room temperature, thus providing an ideal system for potential spintronic applications. Here we report the synthesis of a new compound, Cr0.82Te, which demonstrates a record-high topological Hall effect at room temperature in this family. Cr0.82Te displays soft ferromagnetism below the Curie temperature of 340 K. The magnetic measurement shows an obvious magneto-crystalline anisotropy with the easy axis located in the ab plane. The anomalous Hall effect can be well explained by a dominating skew scattering mechanism. Intriguing, after removing the normal Hall effect and anomalous Hall effect, a topological Hall effect can be observed up to 300 K and reaches up to 1.14 μΩ⋅cm at 10 K, which is superior to most topological magnetic structural materials. This giant topological Hall effect possibly originates from the noncoplanar spin configuration during the spin flop process. Our work extends a new Cr x Te y system with topological non-trivial magnetic structure and broad prospects for spintronics applications in the future.

Fabrication of magnetic field sensor based on a Co-based Schottky heterojunction

We have prepared a reliable magnetic field sensor based on a Co-based Schottky heterojunction with the possibility of finding practical application when the current–voltage (I–V) characteristics of the heterojunctions were modified by the external magnetic fields. For this purpose, the heterojunctions based on ferromagnetic thin films Co were deposited on Si (100) substrate via ultra-thin Pt films. The structural and magnetic properties of the heterojunctions were demonstrated, the crystal structure and the saturation magnetization of heterojunctions significantly increased with the increase of annealing temperatures. The electrical properties of the Co/Pt/Si heterojunction were investigated using temperature-dependent I–V characteristics, the rectifying properties were observed in the whole temperature ranging from 233 K to 283 K. Based on a simplified energy band structure, the magnetic field transport properties of Co/Pt/Si heterojunctions were investigated by taking into account the effects of spin and magnetic field on the potential barrier height of Co/Pt/Si heterojunctions. The results showed that the experimental ratio of current measured in a magnetic field B and in zero magnetic field (I(B)/I(0)) is linearly with the magnetic field B and almost independent of the applied voltage. The sensitivity and linearity of the magnetic field sensor were measured. The sensitivity of the sensor can reach 72.09 μA/T at an applied voltage frequency of 2000 Hz, which indicates that the linearity and sensitivity of the sensor are improved with the increase of the applied voltage frequency. The proposed sensors would be easy to integrate with current semiconductor processes with simple structure and they could be suitable for geological applications such as energy exploration.

Observation of skyrmion-induced topological Hall effects in Mn3.5Au0.5N films

The Mn4-xAuxN films were grown on MgO(001) substrates by plasma assisted molecular beam epitaxy. The magnetic characteristics and spin transport properties are systematically studied. A sign reversal of anomalous Hall coefficient is observed at 160 K in Mn3.5Au0.5N. This phenomenon can be attributed to the competition between electron-like and hole-like anomalous Hall effects (AHEs). The mutual eliminating of electron-like and hole-like AHEs gives rise to zero resistivity of 160 K at high field. A butterfly-like curve with two humps is observed at 160 K, which can be ascribed to the skyrmion-induced topological Hall effects (THEs). It is thus confirmed that the transverse resistivity in Mn3.5Au0.5N comprises of three components: electron-like AHEs, hole-like AHEs, and skyrmion-induced THEs. An effective method was employed to analyze THEs in the material systems that contain both electrons and holes. The THEs in Mn3.5Au0.5N can be observed after electron-like AHEs are subtracted down from transverse resistivity.

Magnetic and electrical transport properties in GdAlSi and SmAlGe

Abstract In this work, we conduct a detailed examination of the magnetic and electrical transport properties in GdAlSi and SmAlGe crystals, which possess a LaPtSi-type structure (space group I41 md). The magnetic susceptibility data unambiguously reveal magnetic ordering below a characteristic transition temperature (T N ). For GdAlSi, a hysteresis loop is observed in the magnetization and magnetoresistance curves within the ab plane when the magnetic field is applied below T N , which is around 32 K. Notable specific heat anomalies are detected at 32 K for GdAlSi and 6 K for SmAlGe, confirming the occurrence of magnetic transitions. Besides, the extracted magnetic entropy at high temperatures is consistent with the theoretical value of Rln(2J+1) for J = 7/2 in Gd3+ and J = 5/2 in Sm3+, respectively. SmAlGe also exhibits Schottky-like specific heat contributions. Additionally, both GdAlSi and SmAlGe exhibit positive magnetoresistance and a normal Hall effect.

β-Phase Yb5Sb3Hx: Magnetic and Thermoelectric Properties Traversing from an Electride to a Semiconductor.

An electride is a compound that contains a localized electron in an empty crystallographic site. This class of materials has a wide range of applications, including superconductivity, batteries, photonics, and catalysis. Both polymorphs of Yb5Sb3 (the orthorhombic Ca5Sb3F structure type (β phase) and hexagonal Mn5Si3 structure type (α phase)) are known to be electrides with electrons localized in 0D tetrahedral cavities and 1D octahedral chains, respectively. In the case of the orthorhombic β phase, an interstitial H can occupy the 0D tetrahedral cavity, accepting the anionic electron that would otherwise occupy the site, providing the formula of Yb5Sb3Hx. DFT computations show that the hexagonal structure is energetically favored without hydrogen and that the orthorhombic structure is more stable with hydrogen. Polycrystalline samples of orthorhombic β phase Yb5Sb3Hx (x = 0.25, 0.50, 0.75, 1.0) were synthesized, and both PXRD lattice parameters and 1H MAS NMR were used to characterize H composition. Magnetic and electronic transport properties were measured to characterize the transition from the electride (semimetal) to the semiconductor. Magnetic susceptibility measurements indicate a magnetic moment that can be interpreted as resulting from either the localized antiferromagnetically coupled electride or the presence of a small amount of Yb3+. At lower H content (x = 0.25, 0.50), a low charge carrier mobility consistent with localized electride states is observed. In contrast, at higher H content (x = 0.75, 1.0), a high charge carrier mobility is consistent with free electrons in a semiconductor. All compositions show low thermal conductivity, suggesting a potentially promising thermoelectric material if charge carrier concentration can be fine-tuned. This work provides an understanding of the structure and electronic properties of the electride and semiconductor, Yb5Sb3Hx, and opens the door to the interstitial design of electrides to tune thermoelectric properties.

Crystal growth, magnetic and electrical transport properties of the kagome magnet RCr6Ge6 (R = Gd–Tm)

Abstract Kagome magnets have attracted considerable research attentions due to the interplay between topology, magnetism and electronic correlations. In this study, we report single crystal synthesis of a series of the kagome magnets RCr6Ge6 (R = Gd - Tm) which possess defect-free Cr kagome lattices, and systematically study their magnetic and electrical transport properties. The transition from canted ferrimagnetic to paramagnetic state in GdCr6Ge6, TbCr6Ge6, DyCr6Ge6, HoCr6Ge6, ErCr6Ge6, and TmCr6Ge6 occurs at 11.3 K, 10.8 K, 4.3 K, 2.5 K, 3.3 K, and below 2 K, respectively, due to R-R interactions within the compounds. Magnetization measurements reveal highly anisotropic magnetism with canted magnetic moments in these compounds. In the electrical transport, both negative and positive magnetoresistance at different magnetic field and temperature have been observed due to the competition between different scattering mechanisms. Our work enriches understandings on the Cr-based kagome magnets and paves way for searching possible topological responses in this family.

The magnetic and electric transport properties in erbium-doped layered perovskite iridate Sr2–xErxIrO4

The 5d oxide Sr2IrO4 with a layered perovskite structure has been investigated due to its peculiar Jeff = 1/2 insulating ground state. In this research, we investigate the evolution of magnetic and electric transport properties of Er-doped polycrystalline perovskite iridates Sr2–xErxIrO4 (0 ≤ x ≤ 0.06). Er3+ is magnetic and can thus provide magnetic interactions with Ir. Also, Er3+ doping introduces a carrier-doping effect. We find that substituting Sr2+ with Er3+ still preserves the I41/acd crystal structure, while it causes the rotation of IrO6 octahedra φ to decrease. In this case, the Ir–O1–Ir bond angle increases and the tetragonal distortion c/a decreases. The magnetic properties present a suppressed transition temperature, a decreased Curie–Weiss temperature, and an increased effective magnetic moment. The electrical resistivity of the doped samples decreases with doping, which originates from the crystal distortion and electron doping. Theoretical calculations represent an increase in band filling and an improvement in the conduction property with doping.

Studies on the microstructure, magnetic, and electrical transport properties of Dy-substituted Mg–Cu–Zn ferrites

Studies on the microstructure, magnetic, and electrical transport properties of Dy-substituted Mg–Cu–Zn ferrites

Topological stability of spin textures in Si/Co-doped helimagnet FeGe

Element substitutions with magnetic or non-magnetic atoms are known to significantly impact the magnetic structure and related transport properties of magnets. To clarify the change of magnetic structure of B20-type magnets with element doping, we conduct real-space observations of spin textures and their temperature (T)-magnetic field (H) phase diagrams of a helimagnet FeGe with partially substituting Fe and Ge with Co and Si, respectively. The helical period (λ) changes dramatically by the element doping: λ increases by 147% to 103 nm in 30% Co-doped FeGe, whereas it decreases by around 70% to 49 nm in 30% Si-doped FeGe, compared to the λ =70 nm in FeGe. Upon applying the magnetic field normally to (001), (110), and (111) thin plates of both FeSi0.3Ge0.7 and Fe0.7Co0.3Ge, the hexagonal skyrmion crystal (SkX) state emerges. The magnetic phase diagrams observed through the real-space imaging reveal that (1) the SkX can extend to a larger T-H window by reducing the sample thickness or by cooling the sample under specific magnetic fields from temperatures above the transition temperature (TC ); (2) the stability of the SkX phase differs between Si-doped and Co-doped FeGe: the SkX phase is most unstable in the (111) FeSi0.3Ge0.7, while it remains robust in the (111) Fe0.7Co0.3Ge. These differences indicate distinct anisotropic behavior in FeGe with magnetic (Co) and non-magnetic-element (Si) dopants.

Intertwined crystal structure, magnetic, and charge transport properties in mixed valent A-site ordered manganite NdBaMn2O6

In the present work, we report a correlation between crystal structure, magnetic, and electrical properties in an exotic magnetic compound, NdBaMn2O6 having ∼92% ordering between Nd and Ba, investigated using temperature-dependent synchrotron x-ray diffraction (XRD), dc magnetization and transport measurements. Temperature-dependent XRD data reveals that the compound undergoes various complex crystallographic phase transitions from high-temperature (T > 320 K) P4/mmm phase to intermediate (320 K – 280 K) Cmmm phase to a mixed (Cmmm and P21am) phase (280 K – 220 K) and to low-temperature P21am phase (T < 220 K). It is found that these crystallographic phase compositions play a crucial role in controlling its magnetic and transport properties. Temperature-dependent dc magnetization data show a sharp drop at the onset of mixed phase (Cmmm + P21am) at 280 K followed by a broad hump at ∼ 220 K where mixed phase to P21am transition occurs, thus indicating a correlation between the structural and magnetic properties. The dc magnetization in the mixed phase region is calculated by considering a superposition of the magnetic moments of Cmmm and P21am phases weighted by the fraction of each phase, which exactly follows the experimental magnetization data. Temperature variation of resistivity data shows a jump at ∼260 K, a temperature corresponding to 50–50% phase composition of Cmmm and P21am phases. The compound shows insulating behavior over a whole temperature range as confirmed from the resistivity data. Further, application of magnetic field causes a shift of magnetic and transport transition temperatures which may be due to the magnetic field induced structural transition in the system.

Unusual anomalous Hall effect in SrRuO3 films with linear out-of-plane Ru vacancies gradient

The manipulation of magnetic transport properties has been one of the central problems in spintronics. However, the modulation of Hall signals in thin films has stringent requirements on their thickness and means of growth. Here, a series of inhomogeneous SrRuO3 thin films with different paths of linear out-of-plane Ru vacancies gradient was designed to generate an unusual anomalous Hall effect (UAHE) under broad growth conditions. Combining x-ray diffraction and magnetic data, it was concluded that the appearance of UAHE was not a simple superposition of AHE caused by multiple magnetic phases. The interaction between these magnetic phases in the linear-vacancies-gradient SrRuO3 films was analyzed by the first-order reversal curve (FORC) method, and it was found that the change trend of FORC was the same as that of UAHE. Such out-of-plane linear-vacancies-gradient thin film provides a way to regulate the different phases by introducing the cation vacancies distribution in an orderly way to control their magnetic and transport properties in oxide films. Furthermore, a distinctive perspective on the origin of UAHE was obtained by combining FORC with UAHE.

Bipolar magnetic semiconductor and doping controllable spin transport property in 2D CoI2/MnBr2 heterostructure

The integration of two-dimensional heterostructure materials remains a fundamental way for the manipulation of spintronics in practical applications. Here, we predicted the transform of stripy antiferromagnetic (AFM) CoI2 and MnBr2 monolayers to interlayer AFM CoI2/MnBr2 heterostructure with intralayer ferromagnetic orders by using density functional theory. Interestingly, the CoI2/MnBr2 heterostructure exhibits a typical bipolar magnetic semiconducting state with type-I band alignments. Moreover, the half-metal/semiconductor transition and spin-up/spin-down polarization switching in CoI2/MnBr2 heterostructure can be effectively triggered by electron/hole doping. Our study provides the potential of AFM spintronics for information storage and processing.

Analysis of the Electronic, Magnetic, Elasto‐Mechanical, Thermoelectric, and Thermodynamic Potential of Ruthenium‐Based Full Heusler Alloys Ru2MnX (X = V and Nb)

In the search for new and novel materials for various thermo‐physical applications, we have reported the magnetic, electronic, mechanical, thermal, and thermoelectric transport properties of two full Heusler alloys (HAs), Ru2MnV and Ru2MnNb. In order to obtain a stable structure, volume optimization was carried out in the Fm‐3m (225) and F43‐m (216) space groups. The Fm‐3m space group was found to be a stable phase for both alloys. Electronic results show the metallic nature of these alloys. Ferromagnetic moments of 4.06 and 4.18 μB were obtained for Ru2MnV and Ru2MnNb, respectively. Mechanical results show a brittle nature for Ru2MnV and a ductile nature for Ru2MnNb with a high melting temperature for Ru2MnV. Thermoelectric properties such as figure of merit along with Seebeck coefficient, electrical conductivity, power factor, and thermal conductivity have also been calculated. Furthermore, the thermodynamic results of the studied materials have also been evaluated to understand the nature of various thermodynamic parameters with respect to temperature and pressure.

Variations in perpendicular magnetic and electrical transport properties of ferrimagnetic (0 0 1) NiCo2O4 films

We fabricated epitaxial NiCo2O4 films on (001) MgAl2O4 substrates by varying the pulsed-laser energy density from 1.31 to 2.46 J/cm2, while keeping all other parameters fixed. X-ray diffraction measurements revealed that the increase in energy density increased the film deposition rate from 0.022 to 0.078 nm/s, while resulting in the decrease of the full-width at half-maximum of the rocking curve and out-of-plane lattice constant. At room temperature, the films grown at an intermediate energy density range of 1.97–2.13 J/cm2 exhibited more distinctive perpendicular magnetic anisotropy and magnetic domain structure compared to those grown at high or low energy densities. On the other hand, the lower the laser energy density, the more pronounced the perpendicular magnetic anisotropy becomes at low temperatures. In addition, the ferrimagnetic-to-paramagnetic transition temperature of the film increased with the energy density, reaching a maximum of approximately 390 K at energy densities above 2.13 J/cm2. Furthermore, temperature-dependent resistivity indicated that the metallic behavior in the films grown above 2.13 J/cm2 was retained up to ∼ 500 K, which is much higher than the ferrimagnetic transition temperature. These results suggest that pulsed-laser energy density can serve as an alternative parameter for controlling the perpendicular magnetic properties and enhancing the metallic behavior of the (001) NiCo2O4 film.

Spin-selective transport in edge-passivated zigzag magnesium dichloride nanoribbons: Towards bipolar spin diode and spin rectification devices

In the present work, we investigate the electronic, magnetic, and spin transport properties of zigzag MgCl2 (ZMgCl2) nanoribbons with different types of edge passivation using first-principles calculations based on density functional theory and non-equilibrium Green’s function techniques. Our findings reveal that the ZMgCl2 nanoribbon with Cl edges (ClαClα) and Mg edges (MgMg) exhibits distinct properties depending on the type of passivation. Passivation with O and F on ClαClα edges transforms the nanoribbon into a magnetic semiconductor. Passivation with H and F on MgMg edges results in a semiconductor behavior, B passivation leads to a half-metal behavior, and O passivation to a magnetic semiconductor. Additionally, our transport simulations demonstrate that the ClαClα-F nanoribbon operates as a single spin filter under bias voltage. For the MgMg-B nanoribbon, the behavior varies depending on the magnetic configuration of the electrodes. In the parallel configuration, MgMg-B also functions as a single spin filter, whereas in the antiparallel configuration, it operates as a dual spin filter device. Overall, our results highlight the remarkable potential of two-dimensional MgCl2 for spintronics applications, emphasizing the influence of edge passivation on the electronic and transport properties of nanoribbons.

Introducing gradient Er ions and oxygen defects into SrCoO3 for regulating structural, electrical and magnetic transport properties.

The SrCoO3-δ system has broad application potential due to its diverse crystal structures, oxidation stoichiometric ratio, and significant electrical and magnetic properties. However, it faces the challenges of a complex crystal structure and oxygen defect control in this material system. Herein, we introduce oxygen defects into SrCoO3-δvia Er doping to regulate the structural, electrical and magnetic transport properties. Sr1-xErxCoO3-δ (x = 0-0.25) undergoes an evolution of structure and oxygen content (measured using the iodometric method) from hexagonal SrCoO2.626 (H + Co3O4) to cubic perovskite Sr0.9Er0.1CoO2.689 (CP) and finally to ordered tetragonal Sr0.8Er0.2CoO2.635 (OT). Among the three phases, Sr0.9Er0.1CoO2.689 (CP) exhibits the lowest resistivity, only 4.06 mΩ cm at room temperature, which is attributed to its high three-dimensional symmetry, overlap of O 2p and Co 3d orbitals at high oxygen ion concentration. Further introduction of Er ions and oxygen defects promotes the transformation from low spin Co4+ (LS, t52ge0g, S = 1/2) to high spin Co3+ (HS, t42ge2g, S = 2), and from the CoO6 octahedron (low magnetic moment transformation) to the CoO4.25 tetrahedron (high magnetic moment). The oxygen-deficient CoO4.25 layer appears, which can enhance the ordering of A sites and oxygen vacancies, and the CP phase transforms into room-temperature ferromagnetic Sr0.8Er0.2CoO2.635 (OT, TC∼330 K). Er ions provide unpaired electrons in the 2f orbital, which results in a strong magnetization of Sr0.8Er0.2CoO2.635 (OT, 4.66 μB/Co) at low temperatures.

Single-crystal growth, structure and thermal transport properties of the metallic antiferromagnet Zintl-phase β-EuIn2As2.

Zintl-phase materials have attracted significant research interest owing to the interplay of magnetism and strong spin-orbit coupling, providing a prominent material platform for axion electrodynamics. Here, we report the single-crystal growth, structure, magnetic and electrical/thermal transport properties of the antiferromagnet layer Zintl-phase compound β-EuIn2As2. Importantly, the new layered structure of β-EuIn2As2, in rhombohedral (R3̄m) symmetry, contains triangular layers of Eu2+ ions. The in-plane resistivity ρ(H, T) measurements reveal metal behavior with an antiferromagnetic (AFM) transition (TN ∼ 23.5 K), which is consistent with the heat capacity Cp(H, T) and magnetic susceptibility χ(H, T) measurements. Negative MR was observed in the temperature range from 2 K to 20 K with a maximum MR ratio of 0.06. Unique 4f7J = S = 7/2 Eu2+ spins were supposed magnetically order along the c-axis. The Seebeck coefficient shows a maximum thermopower |Smax| of about 40 μV K-1. The kink around 23 K in the Seebeck coefficient originates from the effect of the antiferromagnetic phase on the electron band structure, while the pronounced thermal conductivity peak at around 10 K is attributed to the phonon-phonon Umklapp scattering. The results suggest that the Eu2+ spin arrangement plays an important role in the magnetic, electrical, and thermal transport properties in β-EuIn2As2, which might be helpful for future potential technical applications.

Enhanced magnetic anisotropy and high hole mobility in magnetic semiconductor Ga1-x-y Fe x Ni y Sb

(Ga,Fe)Sb is a promising magnetic semiconductor (MS) for spintronic applications because its Curie temperature (T C) is above 300 K when the Fe concentration is higher than 20%. However, the anisotropy constant K u of (Ga,Fe)Sb is below 7.6 × 103 erg/cm3 when Fe concentration is lower than 30%, which is one order of magnitude lower than that of (Ga,Mn)As. To address this issue, we grew Ga1-x-y Fe x Ni y Sb films with almost the same x (≈24%) and different y to characterize their magnetic and electrical transport properties. We found that the magnetic anisotropy of Ga0.76-y Fe0.24Ni y Sb can be enhanced by increasing y, in which K u is negligible at y = 1.7% but increases to 3.8 × 105 erg/cm3 at y = 6.1% (T C = 354 K). In addition, the hole mobility (µ) of Ga1-x-y Fe x Ni y Sb reaches 31.3 cm2/(V∙s) at x = 23.7%, y = 1.7% (T C = 319 K), which is much higher than the mobility of Ga1-x Fe x Sb at x = 25.2% (µ = 6.2 cm2/(V∙s)). Our results provide useful information for enhancing the magnetic anisotropy and hole mobility of (Ga,Fe)Sb by using Ni co-doping.

Characteristics of magnetic field sensor utilizing Co-based Schottky contacts

We have explored an approach to constructing reliable magnetic field sensors based on cobalt-based Schottky contacts, which has the potential to find practical applications when an applied magnetic field modifies the current–voltage (I–V) characteristics of heterostructures. For this aim, heterostructures based on a ferromagnetic film Co were deposited on a Si(100) substrate by means of an ultrathin Pt film. The electrical properties of Co/Pt/Si heterojunctions were investigated using temperature-dependent I–V characteristics. The magnetic transport properties of Co/Pt/Si heterojunctions have been investigated, and the results show that the experimental ratio of current, I(B)/I(0), measured in magnetic field B and zero field, is linearly related to magnetic field B and almost independent of the applied voltage. Detailed measurements of the sensitivity and linearity of a heterojunction-based self-referencing magnetic field sensor were performed. The results show that the linearity and sensitivity of the sensor increase with an increase in the applied voltage frequency, and the sensitivity of the sensor reaches up to 72.09 μA/T at a voltage frequency of 2000 Hz. The sensor is easy to integrate with existing semiconductor processes, has a simple structure, and can be used for geological applications such as energy exploration.

Al 0.3 Ga 0.7 N/GaN HEMT Yapısı için QMSA Metodu Uygulanması

In this study, Al 0.3 Ga 0.7 N/GaN high electron mobility transistor (HEMT) structure is grown on a sapphire (Al2O3) substrate by using metal-organic vapor phase epitaxy (MOVPE), and its electron transport and magnetic transport properties are investigated. Resistivity is measured in the 20-350 K temperature range. Hall mobility and Hall carrier concentration are measured in the 0-1.5 T magnetic field range and the same temperature range. Magnetic transport properties are analyzed using quantitative mobility spectrum analysis (QMSA). 2DEG and 3DEG transport mechanisms are separated by using QMSA results.