Field-cooled Measurements Research Articles

Berry curvature induced spontaneous and topological-like Hall effect in magnetic Weyl semimetallic Nd2Ir2O7 (111) thin films

We report a study of longitudinal resistivity, anisotropic magnetoresistance (MR), and Hall effect on epitaxial Nd2Ir2O7 (111) thin films grown by the solid phase epitaxy technique, in which spin–orbit coupling, electronic correlation, magnetic frustration, and f-d exchange interaction are present. Temperature-dependent longitudinal resistivity (ρxx) data indicate semimetallic charge transport in the low-temperature region. Field-cooled longitudinal resistivity measurements detect negligible domain-wall conductance compared to the polycrystal or single-crystal samples. Angle-dependent MR measurement shows that the magnetic structure of Ir4+ 5d moments can be finely tuned by applying a magnetic field along different crystallographic directions. MR measurements show a field-induced modification of the Nd3+ 4f spin structure from all-in-all-out/all-out-all-in (AIAO/AOAI) (4-in-0-out) to 1-in-3-out for the applied field (H) along the [111] direction, resulting in field-induced plastic deformation of the Ir4+ domain distribution. In contrast, the application of field (H) along the [001] and [011] directions could not modify any domain distribution. A large spontaneous Hall effect (SHE) signal has been observed on Nd2Ir2O7 (111) thin film with AIAO/AOAI antiferromagnetic ordering for the application of field (H) along [001], [1̄1̄0], and [111] directions. The appearance of a large spontaneous Hall signal for the applied field along [001] and [1̄1̄0] directions rules out domain switching as the origin of the Hall effect and confirms the presence of the Weyl semimetallic phase in Nd2Ir2O7 (111) thin films. In addition to SHE, a large topological-like Hall signal is also observed, possibly due to the presence of multiple Weyl nodes in the electronic band structure.

Characterization of YBa2Cu3O7−δ coplanar resonator for microwave kinetic inductance detectors

We demonstrate an improved YBa2Cu3O7−δ -based microwave kinetic inductance detector with a quality factor and noise equivalent power, at 10 K. Zero field cooled (ZFC) and field cooled (FC) measurements of the magnetic field dependence of the resonance characteristics, show substantially different behavior, indicating that both the screening currents and vortices play a role. The ZFC measurements exhibit a sharp decrease of the resonance frequency, , and at low fields, up to the full penetration field, revealing the dominant role of the screening currents. In contrast, the FC measurements exhibit a moderate decrease of and with field, revealing the role of vortices and reflecting the field dependence of the penetration depth in a d-wave superconductor.

Synthesis and Characterization of Magnetic Composite Theragnostics by Nano Spray Drying.

Composites of magnetite nanoparticles encapsulated with polymers attract interest for many applications, especially as theragnostic agents for magnetic hyperthermia, drug delivery, and magnetic resonance imaging. In this work, magnetite nanoparticles were synthesized by coprecipitation and encapsulated with different polymers (Eudragit S100, Pluronic F68, Maltodextrin, and surfactants) by nano spray drying technique, which can produce powders of nanoparticles from solutions or suspensions. Transmission and scanning electron microscopy images showed that the bare magnetite nanoparticles have 10.5 nm, and after encapsulation, the particles have approximately 1 μm, with size and shape depending on the material’s composition. The values of magnetic saturation by SQUID magnetometry and mass residues by thermogravimetric analysis were used to characterize the magnetic content in the materials, related to their magnetite/polymer ratios. Zero-field-cooling and field-cooling (ZFC/FC) measurements showed how blocking temperatures of the powders of the composites are lower than that of bare magnetite, possibly due to lower magnetic coupling, being an interesting system to study magnetic interactions of nanoparticles. Furthermore, studies of cytotoxic effect, hydrodynamic size, and heating capacity for hyperthermia (according to the application of an alternate magnetic field) show that these composites could be applied as a theragnostic material for a non-invasive administration such as nasal.

Quenching of spin-orbit coupling and signature of Griffiths Phase in nanocrystalline La0.6Ba0.4MnO3 perovskite manganite

The size-dependent structural and magnetic properties of nano and bulk samples of 40 ​mol% Ba2+-doped LaMnO3 (i.e., La0.6Ba0.4MnO3) manganite have been investigated in detail. The Rietveld refinement of X-ray diffraction data confirms that nano and bulk La0.6Ba0.4MnO3 manganites crystallize into ideal cubic perovskite structure with Pm3¯m space group. The refined unit cell parameters decrease with increasing calcinations temperature or particle size. The temperature dependent magnetization measurements reveal that both the bulk and nano samples exhibit paramagnetic (PM) to ferromagnetic (FM) phase transition at Curie temperature (TC). A distinct bifurcation between magnetization curves under zero-field cooled (MZFC) and field-cooled (MFC) measurements reveals the possible existence of frustrated magnetic ordering or spin glass clusters. For nano sample, a sharp downward deviation in inverse susceptibility from Curie-Weiss law is observed, which indicates the existence of Griffiths Phase. The analysis of the field dependent magnetization M(H) curves measured at 10 ​K, in terms of saturation moments, reveals that there is a coupling between spin and orbital magnetic moments, in bulk sample of La0.6Ba0.4MnO3 manganite, which can be quenched by reducing particle size of the manganite. According to the Banerjee's criterion, nano sample exhibits first-order magnetic transition and bulk sample shows second-order magnetic transition in the low magnetic field region.

Preparation and study magnetic properties of the nanosized ferrite Zn0.5Mn0.5Fe1.95Mo0.02Tb0.01Sm0.01Gd0.01O4 with negative magnetization. A new result

ABSTRACT This work, concern the studies of the local atomic structure of the rare-earth doped Zn-Mn ferrite (Zn0.5Mn0.5Fe1.95Mo0.02Tb0.01Sm0.01Gd0.01O4), characterization techniques such as thermogravimetric analysis, X-ray diffraction (XRD), and Magnetic Properties Measurement System (MPMS), allowed us the effect of rare earth and their impacts on the structure, the size of nanocrystals, and the magnetic properties of the formed nano-ferrite. The XRD analysis showed that a single-phase was obtained at a low temperature of 500°C, with an environmentally friendly process, and nanometric size (8 nm). Magnetic measurements show a superparamagnetic behavior at 80 and 300 K and a week ferrimagnetism at 5 K. Furthermore, these measurements showed that this sample exhibits negative magnetization under zero-field cooled measurements (ZFC) with a low applied field (100 Oe), while the magnetization remains positive under field-cooled (FC) measurement conditions for the same applied field, which is a new result never observed in the case of Zn-Mn doped nano-ferrite.

A high-performance dysprosium(III) single-ion magnet with quasi-Oh symmetry

A {Zn2Dy} single-ion magnet (SIM) with octahedral coordination geometry (Oh) was synthesized and characterized. The zero-field-cooled (ZFC) and field-cooled (FC) magnetic susceptibility measurement diverged below 4.1 K, revealing the presence of the magnetic blocking. Combining experimental data and ab initio calculations, we depicted the dynamic relaxation characters of this complex in detail.

Interfacial magneto-plasticity in partially oxidized magnetite inferred from linear and nonlinear dielectric response

In partially oxidized polycrystalline magnetite, defects/dislocations are formed at the grain/interphase boundaries among the remaining magnetite and oxidized phases. Here, the studied sample is a pellet with the composition of Fe3O4 and α-Fe2O3(3:7), which is obtained by annealing partially air-oxidized polycrystalline Fe3O4. To probe the dislocation behavior in it under the magnetic field, linear and nonlinear dielectric spectroscopy has been utilized under three conditions: before applying the magnetic field, under a magnetic field after cooling at the same field, and after removing the magnetic field. An excessive qualitative and quantitative difference between the dielectric data—both linear and nonlinear harmonic components—taken in the first two protocols has been observed. The dielectric data feature remains like the field-cooled measurement after magnetic field withdrawal. In the field-cooled dielectric frequency spectrum, grain boundary relaxation shows a glass transition above 110 K. This phenomenon occurs mainly due to the plastic deformation through the dislocation movements at the boundaries by the magnetostrictive strain produced in the magnetite grains below the Verwey transition (TV). The dislocations freeze into a glassy phase below the TV of magnetite. The interaction among the dislocations and the boundaries are responsible for showing the nonlinear features.

Structural and superconducting analysis of topologically non-trivial alloy of Sn1-xSbx (x=0.4, 0.5, 0.6)

In the present article, we report a comprehensive study of structural and physical properties of binary alloy Sn1-xSbx (x = 0.4, 0.5, 0.6). All the alloys are grown through the self-flux method under well-optimized heat treatment. The as-grown crystals are structurally characterized through Powder X-Ray Diffraction (PXRD), Scanning Electron Microscope (SEM), and Energy Dispersive X-Ray Analysis (EDAX). Simultaneously, the X-Ray Photoelectron Spectroscopy (XPS) is used to probe the surface of the crystals. All the crystals crystallize in rhombohedral structure with the R −3 m space group, as confirmed from Rietveld refined PXRD pattern. Sn1-xSbx is found to have a secondary phase with an elongated unit cell in conjunction with the primary phase for a specific alloy of x = 0.6. These binary systems are considered to be a possible candidate of topological superconductivity as they show the opening of bands near Fermi level with the inclusion of Spin-Orbit Coupling (SOC) protocols in DFT calculations. However, the superconductivity in all samples is confirmed through DC magnetization measurements under Field Cooled (FC) and Zero Field Cooled (ZFC) measurement at 10 Oe magnetic field. The nature of observed superconductivity is determined by isothermal magnetization (M-H) measurements at 2K, in which these binary alloys are proved to be type-II superconductors.

Ecofriendly synthesis, crystal chemistry, electrical, and low-temperature magnetic properties of nano-particles (Li–Cr) for drug delivery and MRI applications

Mixed Li(0.5−x/2)Fe(2.5−x/2)CrxO4 (X = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) nano-ferrite system was synthesized by using Citrate gel auto-combustion method. Structural parameters such as lattice constant, hopping length, and X-ray density were reported and discussed with composition. The surface morphology was presented and explained with TEM analysis and SAED patterns. XRD patterns show the prepared samples are single-phase cubic spinel structure and the average particle size lies between 17 to 27 nm. TEM analysis shows prepared sample are the crystallite formation in nano-size. DC electrical properties presented variation with temperature and composition were discussed and studied well behind the Curie temperature. Magnetic measurements are carryout with VSM (Vibrating Sample Magnetometer), Observations have shown that magnetic properties are strongly influenced due to the substitution of Cr3+ in Lithium ferrites. Two samples Li0.5Cr0.6Fe1.9O4 and Li0.5Cr1.0Fe1.5O4 were subjected to an applied field of 100 Oe between 5 and 375 K temperature for ZFC and FC (Zero Field Cooled and Field Cooled) measurements of magnetization which indicated blocking temperature at around 350 K for both samples beyond which they exhibited super-paramagnetic behavior.

Exchange bias and training effect in an amorphous Zn-Fe-O/nanocrystalline GaFeO3 bilayer thin film

In this paper, I report the exchange bias effect in a bilayer thin film of amorphous Zn-Fe-O (ZFO) and nanocrystalline GaFeO3 (GFO). I deposited the amorphous ZFO layer on top of a nanocrystalline GFO thin film using pulsed laser ablation of a Zinc ferrite (ZnFe2O4) target at room temperature. This bilayer film showed a large exchange bias effect (HE ∼ 418 Oe at 2 K). The exchange bias shift decreased exponentially as the temperature increased and disappeared for T > 30 K. Along with the exchange bias shift, the film also showed enhanced magnetization in Field Cooled (FC) measurements as compared to the Zero Field Cooled (ZFC) magnetization. The magnetization decreased during consecutive M-H loops cycling in training effect measurements. This decrease in the magnetization of the film followed the spin configurational relaxation model. The observed exchange bias effect can be attributed to a unidirectional anisotropy originated due to the pinning effect of the interfacial spins of the ZFO layer.

Heterometallic 3d-4f Complexes as Air-Stable Molecular Precursors in Low Temperature Syntheses of Stoichiometric Rare-Earth Orthoferrite Powders.

Four 3d-4f hetero-polymetallic complexes [Fe2Ln2((OCH2)3CR)2(O2CtBu)6(H2O)4] (where Ln = La (1 and 2) and Gd (3 and 4); and R = Me (1 and 3) and Et (2 and 4)) are synthesized and analyzed using elemental analysis, Fourier transform infrared spectroscopy, thermogravimetric analysis, and SQUID magnetometry. Crystal structures are obtained for both methyl derivatives and show that the complexes are isostructural and adopt a defective dicubane topology. The four heavy metals are connected with two alkoxide bridges. These four precursors are used as single-source precursors to prepare rare-earth orthoferrite pervoskites of the form LnFeO3. Thermal decomposition in a ceramic boat in a tube furnace gives orthorhombic LnFeO3 powders using optimized temperatures and decomposition times: LaFeO3 formed at 650 °C over 30 min, whereas GdFeO3 formed at 750 °C over 18 h. These materials are structurally characterized using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray map spectroscopy, and SQUID magnetometry. EDX spectroscopy mapping reveals a homogeneous spatial distribution of elements for all four materials consistent with LnFeO3. Magnetic measurements on complexes 1-4 confirm the presence of weak antiferromagnetic coupling between the central Fe(III) ions of the clusters and negligible ferromagnetic interaction with peripheral Gd(III) ions in 3 and 4. Zero-field-cooled and field-cooled measurements of magnetization of LaFeO3 and GdFeO3 in the solid-state suggest that both materials are ferromagnetic, and both materials show open magnetic hysteresis loops at 5 and 300 K, with Msat higher than previously reported for these nanomaterials. We conclude that this is a new and facile low temperature route to these important magnetic materials that is potentially universal, limited only by what metals can be programmed into the precursor complexes.

Griffiths phase, magnetic memory and ac susceptibility of an antiferromagnetic titanate-based perovskite Er0.9Sr0.1Ti0.975Cr0.025O3 system

In this study, we investigated different physical properties of Er0.9Sr0.1Ti0.975Cr0.025O3 titanate prepared by a solid-state reaction that produces a cubic structure with Fd-3m (227) as a space group. Zero-Field Cooled and Field Cooled measurements show a second-order antiferromagnetic transition at Neel temperature TN = 23 K, and the existence of Griffiths phase at around TGP = 132 K. This soft magnetic material depicts a magnetic memory since it ‘remembers’ its thermal history. The relative cooling power of this titanate-based sample was then measured to be around 292.27 J kg−1 at 5 Tesla and 400 J kg−1 at 6 Tesla. However, these values are lower than the RCP value reported for the most magnetic refrigerant Gd, although these results are high enough compared to different perovskite systems. Therefore, Er0.9Sr0.1Ti0.975Cr0.025O3 is a very suitable, environment-friendly magnetic refrigerant.

Observation of room temperature ferromagnetism and exchange bias in a 55Mn+ ion-implanted unintentionally doped [formula omitted]-[formula omitted] single crystal

In this manuscript, the structural and magnetic properties of a 55Mn+ ion-implanted unintentionally doped β-Ga2O3 single crystal are investigated. The implanted Mn+ ions cause crystalline degeneration due to the formation of defects in the surface of the substrate. Room temperature ferromagnetism (FM) is observed in the samples with implantation doses of 5 × 1014cm-2, 1 × 1015cm-2 and 5 × 1015cm-2. The zero-field-cooled (ZFC)/field-cooled (FC) measurement of magnetization reveals that the ion implantation process induces an antiferromagnetic (AFM) phase. The temperature evolution of the remanence asymmetry (ME) demonstrates the typical behavior of the exchange bias effect due to the coexistence of FM and AFM phases. Based on the distribution of Mn+ ions and defects and the relationship between the remanence asymmetry (ME) and the exchange bias field (HE), the single domain and core-shell models are used to investigate the exchange bias system. The formation mechanism of the ferromagnetic order is briefly discussed, which is rather different from the one corresponding to the bound magnetic polaron (BMP) model.

Zero field cooled exchange bias effect in nano-crystalline Mg-ferrite thin film

The Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz substrate using pulsed laser ablation technique, is reported. The film showed a high ZFC EB shift (HE ∼ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite thin film also showed the Conventional Exchange Bias (CEB) effect, but unlike many CEB systems, the film showed a decrease in coercivity (HC) under the Field Cooled measurements. The film also showed the training effect in ZFC measurements, which followed the frozen spin relaxation behavior. The observed exchange bias could be attributed to the pinning effect of the surface spins of frozen glassy states at the interface of large ferrimagnetic grains.

Magnetic phase transition from paramagnetic in Nb2AlC-MAX to superconductivity-like diamagnetic in Nb2C-MXene: an experimental and computational analysis.

Transition metal carbides (TMCs) have recently emerged as competent members among the family of two-dimensional (2D) materials, owing to their promising applications. There are many promising applications of MXenes; however, their magnetic properties lack a wide margin, both experimentally as well as theoretically, which needs to be investigated for potential use in spintronics. In this study, we carried out a comprehensive etching process via selective extraction of Al layers from Nb2AlC-MAX using a wet electrochemical route under well-optimized conditions to obtain fine 2D-Nb2C MXene sheets. Structural analysis using X-ray diffraction (XRD) confirms the effective removal of Al followed by confirmation of a 2D layered structure from morphological analysis using scanning electron microscopy (SEM). Zero-field-cooled (ZFC) and field-cooled (FC) measurements of MAX and MXene at different field strengths were performed using a superconducting quantum interference device (SQUID). Magnetic measurements reveal the paramagnetic nature of Nb2AlC-MAX measured under 5 mT; however, this changes to a clear superconductor-like diamagnetic behavior with a shift of the magnetization from positive to negative values at low temperatures when measured under 5 mT and 10 mT for Nb2C MXene. The diamagnetism, however, is changed to paramagnetism at 100 mT, which shows the existence of critical fields known typically for a type-II superconductor. To gain an insight into this unusual behavior in MXene, density functional theory (DFT) first-principles calculation was also performed in Wein2K software using spin-polarized generalized gradient approximation (sp-GGA). The magnetic moment of the compound is calculated to be negative, which corresponds well with the experimental finding and suggests that the negative magnetic moment originated from the d-orbital of Nb2C. The present report provides a pathway to deeply understanding the existence of superconductivity-like diamagnetic behavior in Nb2C MXene, which is useful for future magnetic applications.

Magnetic field dependence of the martensitic transition and magnetocaloric effects in Ni49BiMn35In15

The structural, magnetic, and magnetocaloric properties of the Bi-doped Heusler alloy Ni49BiMn35In15 have been investigated using room temperature X-ray diffraction (XRD) and magnetization measurements in a temperature interval of 5-400 K. The alloy at room temperature was found to be in a mixture of a high temperature austenite phase (AP) and a low temperature martensite phase (MP). A drastic shift in the martensitic transition temperature at the rate of 16 K/T from 197 K to lower temperatures was observed. A kinetic arrest phenomenon of the AP was observed in the magnetization and electrical resistivity measurements during field-cooled (FC) measurements at 5T. A metamagnetic behavior characterized by a jump in magnetization in the isothermal M(H) curves near TM was observed. The maximum value of the magnetic entropy change and refrigerant capacity at Curie temperature were found to be 5.5 Jkg-1K-1 and 312 Jkg-1 for μoΔH = 5T, respectively. A large magnetoresistance value of -56% was found near the martensitic transition.

Reversible Magnetocaloric Effect of (La0.8Pr0.2)0.67Ba0.33MnO3 from Direct Measurements

In this study, magnetic and magnetocaloric properties of (La0.8Pr0.2)0.67Ba0.33MnO3 manganite synthesized by sol-gel method were investigated. Under low magnetic field, temperature-dependent zero-field-cooled, field-cooled, and field-heated measurements were performed and the magnetic phase transition temperature corresponding to the sudden drop in magnetization was determined as 200 K. The magnetic entropy change value of the sample is determined as 2.2 J/kgK in 4.8 T magnetic field from isothermal magnetization curves. The adiabatic temperature change (ΔTad) of the sample was measured directly using an adiabatic calorimeter and measured as 0.72 K with a field change of 3 T. As a result of cyclic measurement of ΔTad, it is observed that the material has a reversible magnetocaloric effect (MCE) during the application and removal of the field 5 times. This reversible MCE property of the material is important in that it is the most desirable property of potential materials to be used in magnetic cooling systems.

Magnetic field enhanced coercivity of Fe nanoparticles embedded in antiferromagnetic MnN films

The exchange coupling effect in nanocomposite samples with ferromagnetic (FM) body-centred tetragonal (bct) Fe nanoparticles (NPs) (~20 nm) embedded in an MnN antiferromagnetic (AFM) matrix is investigated. Both the bct Fe NPs control sample and the MnN (×nm)\\bct Fe NPs\\MnN (20–35 nm)\\Ta (5 nm) nanocomposite samples are synthesized by a gas-phase condensation method. Both the coercivity and the remanence ratio of the nanocomposite samples are significantly enhanced compared with the bct Fe NPs sample. The coercivity and the remanence ratio increase with MnN thickness up to 30 nm and then decrease. Additionally, the exchange coupling strength between the bct Fe NPs and AFM MnN matrix is enhanced by magnetic field training. The magnetic field training leads to a higher coercivity and remanence ratio after one cycle of field-cooled hysteresis loop measurement. The coercivity of the composite sample increases by 80%, while the remanence ratio increases by around 30% compared with the bct Fe NPs sample. This work may provide an alternative approach to the design and manufacturing of FM-AFM exchange-coupled permanent magnets.

Effect of α-Fe₂O₃ Phase on the Magnetic Interactions in Nickel Ferrite (NiFe₂O₄) Nanoparticles.

We report on the effect of α-Fe₂O₃ phase in the magnetic properties and magnetic interactions in nickel ferrite (NiFe₂O₄-NFO) nanoparticles synthesized by co-precipitation method. Structural analysis confirms the formation of the cubic inverse spinel phase without any impurities for the NFO sample annealed in air at 650 °C. When the annealing temperature is increased to 750 °C and 850 °C, α-Fe₂O₃ impurity phase is formed along with the parent NFO phase. Raman spectra recorded at room temperature (RT) confirm the presence of pure NFO phase for the sample annealed at 650 °C, and presence of α-Fe₂O₃ phase is observed in the samples annealed at 750 °C and 850 °C. Saturation magnetization values at RT for the NFO samples annealed at 650 °C, 750 °C and 850 °C are 34 emu/g, 19 emu/g and 28 emu/g respectively. Zero Field Cooled (ZFC) and Field Cooled (FC) measurement reveals the super-paramagnetic behavior along with competing magnetic interactions in all the samples. For the NFO sample annealed at 750 °C and 850 °C, a drop in ZFC magnetization and a small kink in FC magnetization observed around 245 K indicate the presence of a Morin transition (TM) from the α-Fe₂O₃ phase. Anisotropy constants were calculated for all the samples using the law of approach to saturation (LAS) method. The magnetocrystalline anisotropy energy distribution function for the NFO samples annealed at 750 °C and 850 °C exhibit broad peak due to the random distribution of spins associated with different particle size.

AC susceptibility, DC magnetization and superconducting properties of tungsten oxide nanowires added YBa2Cu3Oy

In this report, the impact of tungsten oxide nanowires (noted WO3-NWs) inclusion on the AC susceptibility, DC magnetization and superconducting properties of YBa2Cu3Oy (noted Y-123) was investigated. Non-added and WO3-NWs added to Y-123 samples were produced using solid-state reaction route. Prepared samples were characterized by using numerous techniques, such X-rays diffraction (XRD), scanning electron microscopy (SEM) along with energy-dispersive X-ray (EDX) spectroscopy, electrical resistivity, magnetization hysteresis loops, zero-field cooling and field-cooling (ZFC-FC) magnetizations and AC susceptibility measurements. The successful development of the orthorhombic Y-123 phase was confirmed via XRD and EDX analyses. SEM observations showed that the WO3-NWs provoke an enhancement of the connectivity among grains and reduces the porosity by entering between the grains and filling the voids among them. Measurements of electrical resistivity and ZFC-FC magnetizations verified the manifestation of superconductivity in various samples. The magnetization and intergranular critical current densities (Jcm and Jc,inter) were deduced from various magnetic measurements. Improvements of critical current densities (Jcm and Jc,inter) and flux pinning capability were found with the inclusion of NW-WO3 into Y-123 matrix.