Vibrating Sample Magnetometer Measurements Research Articles

The discovery of two-dimensional (2D) ferromagnetic semiconductors holds significant promise for advancing Moore's law and spintronics in-memory computing, sparking tremendous interest. However, the Curie temperature of explored 2D ferromagnetic semiconductors is much lower than room temperature. Although plenty of 2D room-temperature ferromagnetic semiconductors have been theoretically predicted, there have been formidable challenges in preparing such metastable materials with ordered structures and high stability. Here, utilizing a novel template-assisted chemical vapor deposition strategy, we synthesized layered MnS2 microstructures within a ReS2 template. The high-resolution atomic structure representation revealed that monolayer MnS2 microstructures well crystallize into a distorted T-phase. Room-temperature ferromagnetism was confirmed through vibrating sample magnetometer measurements, microzone magnetism imaging techniques, and transport characterization. Theoretical calculations indicated that the room-temperature ferromagnetism originates from the Mn-Mn short-range interaction. Our observation not only offered the experimental confirmation of the intrinsic room-temperature ferromagnetism in layered MnS2, but also provided an innovative strategy for the growth of 2D metastable functional materials.

A reduced dimensionality of multiferroic materials is highly desired for device miniaturization, but the coexistence of ferroelectricity and magnetism at the two-dimensional limit is yet to be conclusively demonstrated. Here, we used a NbSe2 substrate to break both the C3 rotational and inversion symmetries in monolayer VCl3 and, thus, introduced exceptional in-plane ferroelectricity into a two-dimensional magnet. Scanning tunneling spectroscopy directly visualized ferroelectric domains and manipulated their domain boundaries in monolayer VCl3, where coexisting antiferromagnetic order with canted magnetic moments was verified by vibrating sample magnetometer measurements. Our density functional theory calculations highlight the crucial role that highly directional interfacial Cl-Se interactions play in breaking the symmetries and, thus, in introducing in-plane ferroelectricity, which was further verified by examining an ML-VCl3/graphene sample. Our work demonstrates an approach to manipulate the ferroelectric states in monolayered magnets through van der Waals interfacial interactions.

Fe/GaAs is a prototype system of spin injection at room temperature. The interfacial strain and oriented bonds are both considered the origin of the Fe in-plane uniaxial magnetic anisotropy (UMA), which remains decisive. Here, by the x-ray magnetic circular dichroism (XMCD) and the vibrating sample magnetometer measurements, this study shows that in the Fe/Cr(t)/GaAs structure, the in-plane UMA of Fe originates from the chemical bonding between the Fe and the GaAs substrate by varying Cr thickness, t. The UMA drops as the Cr coverage increases, characterized by a decrease in the saturation field from 2400 to 57 Oe. The XMCD studies reveal that the Fe orbital moment, a signature of chemical bonds, decreases from 0.216 μB at Cr = 0 ML to 0.138 μB at Cr = 5 ML. The reduction of the Fe orbital moment and the UMA are qualitatively consistent, establishing a link between the UMA and the interfacial chemical bonds. The decreased UMA remains unchanged at t > 5 ML, above which Fe and GaAs are fully separated by a continuous Cr layer. Our findings provide clear experimental evidence that the UMA in the Fe/GaAs system originates from the oriented interface bonds, clarifying the UMA origin in this prototype system.

This study investigates the characteristics of cobalt ferrite nanofluids, focusing on their structural, thermal, electrical conductivity, and viscosity properties. The motivation behind this research lies in the potential applications of nanofluids in advanced thermal management systems due to their enhanced properties. Characterization techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, and vibrating sample magnetometer measurements, were employed to analyze the nanofluids. X-ray diffraction results indicate that cobalt ferrite nanoparticles crystallize in a spinel structure with Fd-3 m symmetry. Dynamic light scattering and transmission electron microscopy confirm that the nanoparticles have dimensions of approximately 25 nm and exhibit specific ferromagnetic properties at temperatures below 435 K, as demonstrated by the magnetization curve. Thermal conductivity measurements were conducted across various volume fractions, ranging from 1 to 5%, and under magnetic fields of 0.05 and 0.1 T at temperatures of 300.15, 313.15, and 323.15 K. The findings reveal a significant dependence of thermal conductivity on both magnetic field and temperature. For instance, at 300.15 K, increasing the volume fraction from 1 to 5% results in a rise in thermal conductivity from 0.59 to 0.88 W/m.K, representing a 49% increase. Additionally, applying a magnetic field of approximately 0.1 T increases the thermal conductivity coefficient for a 1% volume fraction from 0.59 to 0.72 W/m.K, leading to a growth of about 22%. The electrical conductivity coefficient also varies with different volume fractions and magnetic field intensities, with a maximum increase of around 11% observed at a 4% volume fraction under a 0.1 T magnetic field. In terms of viscosity, no significant changes were noted for volume fractions below 1.5%, while a slight decrease in dynamic viscosity was observed for higher fractions with increasing magnetic field strength. These results demonstrate that the application of a magnetic field enhances the flow properties of the nanofluid, highlighting its potential for improved thermal management applications.

This study aimed to synthesize MgFe1.9Ln0.1O4 (where, Ln = Yb, Pr, Gd, and Nd) ferrite nanoparticles via the sol-gel process and investigate their structural, morphological, and magnetic properties for potential hyperthermia applications. X-ray diffraction analysis (XRD) confirmed the cubic spinel structure for all samples. Transmission electron microscopy (TEM) images revealed nanometer-scale dimensions and nearly spherical morphology. Vibrating sample magnetometer measurements (VSM) indicated superparamagnetic behavior, with decreasing saturation magnetization (Ms) observed as Ln3+ content decreased. Specific absorption rate (SAR) analysis at 198 kHz demonstrated the influence of Ln3+ substitution on magnetic properties. Compared to existing studies, Ln3+ substituted (Yb, Pr, Gd, and Nd) nanoparticles demonstrate tunable magnetic properties and enhanced SAR performance, offering a more efficient design for hyperthermia treatment of solid tumors.Graphical

Vertical domain wall memory (V-DWM) is an advanced racetrack memory, whose recording density reaches more than 10 Tb･cm-2 due to the racetracks installed vertically [1]. Conventionally, horizontal racetrack memories have been fabricated by dry etching [2-5]. However, ferromagnetic materials are difficult to etch into high-aspect-ratio structure vertically. Therefore, electrodeposition in nanoholes is a suitable process to fabricate V-DWM. In addition, V-DWM has multilayer structures in the vertical racetracks, which improves controllability of domain walls and lowers power consumptions [1]. In the multilayers, magnetic layers with perpendicular magnetic anisotropy (PMA) and those with weak anisotropy are stacked. CoPt alloy is a candidate for the material of V-DWM because its magnetic anisotropy can be altered by changing its composition [6]. Until now, though Co/Pt multilayer films have been fabricated by electrodeposition [7, 8], they do not have both PMA and high coercivity enough for storage medium. In this study, to establish the method of stacking CoPt layers which can be applied to V-DWM, the bilayer film where PMA Co-rich CoPt layer and Pt-rich one were stacked was fabricated, and its structures and magnetic properties were characterized. At first, monolayer Co-rich CoPt films with PMA were electrodeposited on Pt substrates potentiostatically. The plating bath consisted of 1 mM CoSO4, 0.1 mM H2PtCl6, and 0.1 M Na2SO4. The counter and reference electrodes were Pt mesh and Ag/AgCl. The deposition potential was set to -650 mV. Deposition time was varied from 100 to 1300 s and suitable time for PMA was found. From the results of vibration sample magnetometer (VSM) measurements, the electrodeposited CoPt films showed PMA when the deposition time was from 500 to 700 s, and their easy axis changed into in-plane direction from 1100 s. The coercivity of PMA sample deposited for 500 s was 1.5 kOe. Cross-sectional transmission electron microscope (TEM) images showed the thickness of the CoPt film with PMA deposited for 500 s was 6 nm while that with in-plane magnetic anisotropy deposited for 1300 s was 10 nm. Energy dispersive X-ray spectroscopy (EDS) results showed the composition of Co in deposited films were 70-90 at%. Considering that crystal magnetic anisotropy keeps PMA even if the thickness of CoPt film with almost the same composition is 20 nm [9], the deposited film could have weak crystal magnetic anisotropy, which suggests that interface magnetic anisotropy between the CoPt layer and Pt substrate is the cause of the PMA. Next, Pt-rich layer was deposited on the PMA CoPt layer by changing deposition potential from -650 mV to -500 mV. The deposition time of the Pt-rich layer was 2000 s to design its thickness to be 10 nm. A bilayer structure was observed in a TEM bright field image and EDS mapping. The average compositions of top and bottom layers were Co42Pt58 and Co72Pt28, respectively. The total thickness of the bilayer was confirmed to be 12 nm. From VSM measurements, fabricated the bilayer film showed PMA and its coercivity was 1 kOe. However, PMA in the bilayer film was smaller than that of the bottom Co-rich layer. The reason why PMA was weakened would be that large total thickness of bilayer weakened interface anisotropy. However, smaller Co composition of the top layer than that of the bottom layer decreases demagnetization in the film, which could prevent the easy axis to become in-plane direction. Thus, Pt-rich CoPt/Co-rich CoPt bilayer film with PMA and the coercivity of 1 kOe can be fabricated. With this stacking method, CoPt multilayered structures which can be applied for V-DWM will be fabricated in the future.Acknowledgements This work was supported in party JST Strategic Basic Research Programs CREST (No. JR-MJCR31C1). Also, part of this work was the results of using a research equipment (G1026) shared in MEXT Project for promoting public utilization of advanced research of advanced research infrastructure (JPMXS0440500024).

Supraparticles (SPs) consisting of superparamagnetic iron oxide nanoparticles (SPIONs) are of great interest for biomedical applications and magnetic separation. To enable their functionalization with biomolecules and to improve their stability in aqueous dispersion, polymer shells are grown on the SPs' surface. Robust polymer encapsulation and functionalization is achieved via atom transfer radical polymerization (ATRP), improving the reaction control compared to free radical polymerizations. This study presents the emulsion-based assembly of differently sized cubic SPIONs (12-30 nm) into SPs with diameters ranging from ∼200 to ∼400 nm using dodecyltrimethylammonium bromide (DTAB) as the surfactant. The successful formation of well-defined spherical SPs depends upon the method used for mixing the SPION dispersion with the surfactant solution and requires the precise adjustment of the surfactant concentration. After purification, the SPs are encapsulated by growing surface-grafted polystyrene shells via activators generated by electron transfer (AGET) ATRP. The polymer shell can be decorated with functional groups (azide and carboxylate) using monomer blends for the polymerization reaction. When the amount of the monomer is varied, the shell thickness as well as the interparticle distances between the encapsulated SPIONs can be tuned with nanometer-scale precision. Small-angle X-ray scattering (SAXS) reveals that cubic SPIONs form less ordered assemblies within the SPs than spherical SPIONs. As shown by vibrating sample magnetometer measurements, the encapsulated SPs feature the same superparamagnetic behavior as their SPION building blocks. The saturation magnetization ranges between 10 and 30 emu/g and depends upon the nanocubes' size and phase composition.

The effect of Nb doping concentration (0, 1, 2, and 4 at. %) on donor defect‐induced ferromagnetism in ZnO thin films is investigated. The films are deposited on Si(111) substrates utilizing the radio frequency magnetron sputtering. X‐ray diffraction pattern unveils that the films show a pronounced orientation along the (002) direction. The relative intensities of defect‐related bands with that of the ultraviolet band from photoluminescence (PL) spectra show that 2 at. % Nb doping results in a greater number of donor defects (Zni+ and VO+) in the ZnO lattice. The parameters extracted from the electron paramagnetic resonance spectra follow a similar trend. The results from vibrating sample magnetometer measurement indicate that pure ZnO displays diamagnetic nature, whereas Nb‐doped ZnO exhibits a ferromagnetic nature. The saturation magnetization value is found highest for 2 at. % Nb doping, which correlates with the presence of a greater number of donor defects, as supported by the PL and electron paramagnetic resonance results. Images obtained from atomic force microscopy show that the surface roughness of the ZnO thin film reduces upon Nb doping. X‐ray photoelectron spectroscopy validates that Nb is doped in 2 at. % Nb‐doped ZnO thin film with Nb oxidation state of +5.

In this study, magnetic natural zeolite (ZTM) was prepared using the coprecipitation method and dithizone was then immobilized on its surface in less toxic medium of alkaline to yield dithizone-immobilized magnetic zeolite (ZTM-Dtz). The synthesized ZTM-Dtz was characterized by FTIR and XRD, indicating that dithizone was successfully immobilized on the surface of ZTM. Vibrating sample magnetometer measurements showed superparamagnetic properties of either ZTM or ZTM-Dtz with magnetization values of 7.35 and 11.49 emu g−1, respectively. The adsorption kinetics of Pb(II) on both adsorbents followed a pseudo-second-order and their adsorption isotherms were properly described by the Langmuir model. The adsorption capacity of ZTM and ZTM-Dtz were 6.94 and 38.46 mg g−1, respectively, suggesting that dithizone immobilization enhanced the adsorbent capacity more than 5 times. The interaction mechanism between Pb(II) metal ion and ZTM was dominated by ion exchange, whereas that of ZTM-Dtz was mostly hydrogen bonds and complexation. The synthesized material is promising to be developed for the adsorption of heavy metal ions such as Pb(II) because it provides a high adsorption capacity and the adsorbents can be easily separated magnetically after application.

Magnetic response of Ho3+ doped Ni0.4Cu0.6HoyFe2-yO4 spinel ferrites and their correlation with crystallite size

Lipases have been used in industrial processes as biocatalysts for transesterification reactions. The synergism between enzymes and magnetic properties may be reached by using magnetic nanoparticles (MNPs) as support to immobilize them in aggregate structures, denominated by magnetic crosslinked enzyme aggregates (MCLEA). One of the advantages of such supports is the possibility of using magnetic separation for enzyme recovery, reducing costs and allowing reuse in continuous systems. Here, porcine pancreatic lipase (PPL) was immobilized onto functionalized magnetite support (Fe3O4-APTS) with a protein binding efficiency of 78.84%. Physical and chemical properties of the nanoparticles and immobilized lipase were characterized by X-ray diffraction (XDR), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), dynamic light scattering (DLS), zeta potential, vibrating sample magnetometer measurements (VSM), and 57Fe Mössbauer spectroscopy. The immobilized lipase additionally exhibited improved stability across wide pH and temperature ranges compared with free lipase. The immobilized derivate also attained good reusability, maintaining 61.37% of its initial activity after 6 reaction cycles. Through magnetic behavior and also because of its surface modification to crosslinking the enzyme, the MCLEA produced in this work has enhanced the biocatalytic activities of PPL.

Magnetic separation has wide-ranging applications in both mineral processing and recycling industries. Nevertheless, its conventional utilization often overlooks the interplay between mineral and particle characteristics and their impact on operational conditions, ultimately influencing the efficacy of the separation process. This work describes a methodology able to achieve the comprehensive characterization and classification of Waste Electrical and Electronic Equipment (WEEE) slag. The primary objective is to establish a meaningful connection between the distinct properties of slag phases and their influence on the separation process. Our methodology consists of several stages. Firstly, the WEEE slag is sieved into distinct size classes, followed by classification into magnetic susceptibility classes by using the Frantz Isodynamic separator. To quantify the magnetic susceptibility of each class, we used a magnetic susceptibility balance, and to identify paramagnetic and ferromagnetic fractions and phases within these magnetic susceptibility classes, we conducted vibrating-sample magnetometer measurements. Finally, to establish a meaningful link between the magnetic characterization, mineralogical, and particle-level details, Mineral Liberation Analysis was conducted for each magnetic susceptibility class. This in-depth analysis, encompassing both particle properties and magnetic susceptibility classes, provides a better understanding of the separation behavior of different phases and can help to enrich phases with a specific range of magnetic susceptibility values. This knowledge advances progress towards the development of predictive separation models that are capable of bridging the gap between theoretical understanding and practical application in the field of magnetic separation.

In this work, the effect of synthesizing process on the morphology, structure, and magnetic properties of Fe3O4 magnetic nanoparticles have been studied by performing X-ray diffraction, scanning electronic microscopy, and vibrating sample magnetometer measurements. Fe3O4 nanoparticles were synthesized by hydrothermal and solvothermal methods. X-ray diffraction analysis revealed that both samples have cubic crystal phase. However, Fe2O3 impurity peaks were observed in the sample synthesized by hydrothermal method. The crystallite sizes of samples synthesized by hydrothermal and solvothermal methods were approximately 38 and 24 nm, respectively. The scanning electron microscope images show that spherical porous and cubic shape Fe3O4 nanoparticles were obtained by solvothermal and hydrothermal method, respectively. The average particle sizes of Fe3O4 samples synthesized by hydrothermal and solvothermal methods were determined as 220 and 450 nm, respectively. Both samples behave a soft ferromagnetic characteristic having almost zero coercive field. The magnetic saturation values of Fe3O4 nanoparticles synthesized by hydrothermal and solvothermal methods were determined as 28.78 and 77.31 emu/g, respectively. As a result of the characterizations, porous Fe3O4 nanoparticles synthesized by solvothermal method show better crystal structure, morphological and magnetic properties than Fe3O4 nanoparticles synthesized by hydrothermal method.

Preparation of Fe3O4@pectin nanocomposite hydrogel with high heating efficiency for hyperthermia applications

Abstract Magnetite magnetic nanoparticles are prepared using olive leaf extract as a green reducing and stabilizing agents. After reaction the product is heated up to get rid of the organic compounds and get pure magnetite nanoparticles. Differential scanning calorimetry is used to study the phase transformation as a function of heating temperature. Scanning electron microscope and high resolution transmission electron microscope show spherical and crystallized nanoparticles with a size of 5 nm. X‐ray diffraction and Raman and x‐ray photoelectron spectroscopy indicate the formation of Magnetite phase with high cristallinity and purity. The synthesized Magnetite nanoparticles are semiconductors with gap energy around 2 eV. Observed by transmission electron microscope graphite rods with stacked carbon disks are decorated with the prepared nanoparticles and show enhanced photocurrent. The vibrating sample magnetometer measurements indicate that the prepared Magnetite nanoparticles have superparamagnetic behavior. These results are very promising for clinical and water splitting applications.

Abstract Fe40Ni40B20 metallic glass is a key material among the many amorphous systems investigated thus far, owing to its high strength and appealing soft magnetic properties that make it suitable for use as transformer cores. In this study, Fe40Ni40B20 microfibers are fabricated down to 5 µm diameter. Three different melt–spinning wheel velocities: ≈51 m s−1, ≈59 m s−1, and ≈63 m s−1 (MG1, MG2, MG3) are used. Their fully amorphous structure is confirmed using X–ray diffraction, and differential scanning calorimetry (DSC) traces reveal a larger relaxation profile for the higher–quenched microfiber. Vibrating sample magnetometer measurements showed a higher saturation magnetization of 136 emug−1 for annealed metallic glass microfibers with a wheel velocity of 59.66 ms−1. Cylindrical magnetic field shields are obtained by aligning and wrapping the fibers around a cast. The observed anisotropic static field shielding behavior is in accordance with the microfibers' anisotropic nature. Composite samples are also produced by embedding the microfibers in an epoxy matrix to investigate their electromagnetic properties at GHz frequencies. Inclusion of the microfibers increase the composite's attenuation constant by 20 to 25 times, making it an ideal candidate for applications in the communications frequency range.

The sol-gel process was used to produce ferrite Ni0.3Zn0.7Cr2−xFexO4 compounds with x = 0, 0.4, and 1.6, which were then subsequently calcined at several temperatures up to 1448 K for 48 h in an air atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and 57Fe Mössbauer spectrometry were used to examine the structure and magnetic characteristics of the produced nanoparticles. A single-phase pure Ni0.3Zn0.7Cr2−xFexO4 nanoparticle had formed. The cubic Fd3¯m spinel structure contained indexes for all diffraction peaks. The crystallite size is a perfect fit for a value of 165 ± 8 nm. Based on the Rietveld analysis and the VSM measurements, the low magnetization Ms of Ni0.3Zn0.7Cr2−xFexO4 samples was explained by the absence of ferromagnetic Ni2+ ions and the occupancy of Zn2+ ions with no magnetic moments in all tetrahedral locations. Moreover, because of the weak interactions between Fe3+ ions in the octahedral locations, the magnetization of the current nanocrystals is low or nonexistent. According to Mössbauer analyses, the complicated hyperfine structures are consistent with a number of different chemical atomic neighbors, such as Ni2+, Zn2+, Cr3+, and Fe3+ species that have various magnetic moments. A Fe-rich neighbor is known to have the highest values of the hyperfine field at Fe sites, while Ni- and Cr-rich neighbors are responsible for the intermediate values and Zn-rich neighbors are responsible for the quadrupolar component.

Synthesis of nanocrystalline nickel-iron alloys-A novel chemical reduction method

Mg x Ni1−x Fe2O4 (x = 0, 0.25, 0.5, 0.75, 1) spinel ferrite material was analyzed to determine its magnetic properties and structure. X-ray diffraction (XRD), Mössbauer spectroscopy, and vibrating sample magnetometer (VSM) characterization were performed on the samples prepared using the sol–gel method. The results from XRD confirmed the existence of the single-phase cubic spinel structures , as well as the evolution of the crystalline size (D), the lattice parameter (a) and cell volume in compounds. The Mössbauer spectra showed the distribution of cations and changes in the magnetic properties of the sample. VSM measurement revealed that the samples were room-temperature ferromagnetic. Moreover, the saturation magnetization (M s) of the samples changed with the Mg2+ ion content x, and a maximum occured at x = 0.5. Doping with Mg2+ ions increased the transfer of Ni2+ ions to tetrahedral sites, thus increasing the magnetic moment difference between tetrahedral (A) and octahedral (B) sites. Specifically, doping NiFe2O4 with Mg2+ ions can enhance its magnetic properties and enhance its saturation magnetization.

Chromium(III)-doped nickel–ferrite nanoparticles, with the general formula Ni0.5Co0.5CrxFe2−xO4 (x = 0.0, 0.10, and 0.20), were prepared by the sol–gel method. The prepared samples were sintered at 700°C for 5 hr. The XRD result showed that the prepared samples are in single-phase partially inverse cubic spinel ferrite structures with space group Fd3m. From the XRD characterization, the average crystallite size for all samples decreased from 39.54 to 30.42 nm and the lattice parameters are found to be 0.8324, 0.8320, and 0.8314 nm for x = 0.0, 0.10, and 0.20, respectively. The energy dispersive X-ray (EDX) spectroscopy analysis confirmed the presence of all ions as per the stoichiometric ratios. The vibrating sample magnetometer measurements revealed that the saturation magnetization (Ms), remnant magnetization (Mr), and coercive fields are found to be decreased with increasing concentration of Cr3+ ions. The UV–vis spectroscopy analysis showed that the energy bandgap (Eg) increased with increasing the concentration of Cr3+ ion from 1.61 to 1.96 eV. The Fourier transform infrared spectra show the two main absorption bands at 407–424 cm−1 and 547–588 cm−1 corresponding to stretching vibrations of metal–oxygen in the octahedral and tetrahedral sites, respectively.