Natural Magnetic Materials Research Articles

Modification of chitosan-coated magnetic material with glycidyltrimethylammonium chloride and its application as heterogeneous base catalyst for levulinic acid esterification

A magnetically separable solid Lewis base catalyst composed of natural magnetic material, chitosan, and glycidyltrimethylammonium chloride was developed. The catalyst is effective for esterification of levulinic acid to produce ethyl levulinate.

Tumor inhibition via magneto-mechanical oscillation by magnetotactic bacteria under a swing MF.

Since magnetic micro/nano-materials can serve as multifunctional transducers for remote control of cell functions by applying diverse magnetic fields, magnetic cell manipulation provides a highly promising tool in biomedical research encompassing neuromodulation, tissue regeneration engineering and tumor cell destruction. Magnetotactic bacteria (MTB), which contain natural magnetic materials, can sensitively respond to external magnetic fields via their endogenous magnetosome chains. Here, we developed a technique for magnetotactic bacteria-based cell modulation and tumor suppression combined with a swing magnetic field. We enabled MTB cells to recognize and bind to mammalian tumor cells via functional modification with RGD peptides onto the surfaces of MTB cells, and RGD-modified MTB bacteria could interact with the targeted tumor cells effectively. The magnetic torque, which was due to the interaction of the long magnetosome chain inside the MTB bacterial cell and the applied swing magnetic field, could result in obvious swing magnetic behaviors of the modified MTB bacteria bound to tumor cell surfaces and thus subsequently exert a sustained magnetomechanical oscillation on the tumor cell surfaces, which could induce a significant activation of Ca²⁺ ion influx in vitro and tumor growth inhibition in vivo. These findings suggest that MTB cells mediated magnetomechanical stimulation, which is remotely controlled by dynamic magnetic fields, as an effective way to regulate cell signaling and treat tumor growth, which will shed the light on further biomedical applications utilizing whole magnetotactic bacteria.

CHARACTERIZATION OF MAGNETIC PROPERTIES OF IRON SAND PUNTARU BEACH, ALOR REGION-NTT

Iron sand is a source of natural magnetic material which is quite abundant. Iron sand can be useful as a magnetic source material which has the potential as a raw material for using magnetic materials. Iron sand contains non magnetic minerals which can reduce its magnetic properties. Therefore, iron sand sample preparation was carried out by washing NaOH 0,4 M and sand sample size variations. The purpose of this study was to determine the effect of washing and the size of iron sand on the magnetic properties in terms of the increase in magnetic elements. The results of research with XRF (X-Ray Fluoresence) show that iron sand with a size of 120 mesh has a magnetic content of Fe (78.07%) higher than iron sand with a size of 80 mesh with Fe content (34.63%). XRD (X-Ray Diffraction) analysis shows that washing iron sand with a size of 80 mesh gives a quarts phase (SiO 2 ) at 2θ = 27.62° and iron sand washing with a size of 120 mesh gives the main peak magnetite phase (Fe 3 O 4 ) at 2θ = 30.69° with a crystallinity of 15%. VSM (Vibrating Sample Magnetometer) analysis depicted on the hysteresis curve shows that the smaller the particle size of iron sand, the higher the magnetic properties. There are still minor oxides in iron sand as oxide minerals.

Hybrid perfect metamaterial absorber for microwave spin rectification applications

Metamaterials provide compelling capabilities to manipulate electromagnetic waves beyond the natural materials and can dramatically enhance both their electric and magnetic fields. The enhanced magnetic fields, however, are far less utilized than the electric counterparts, despite their great potential in spintronics. In this work, we propose and experimentally demonstrate a hybrid perfect metamaterial absorbers which combine the artificial metal/insulator/metal (MIM) metamaterial with the natural ferromagnetic material permalloy (Py) and realize remarkably larger spin rectification effect. Magnetic hot spot of the MIM metamaterial improves considerably electromagnetic coupling with spins in the embedded Py stripes. With the whole hybridized structure being optimized based on coupled-mode theory, perfect absorption condition is approached and an approximately 190-fold enhancement of spin-rectifying photovoltage is experimentally demonstrated at the ferromagnetic resonance at 7.1 GHz. Our work provides an innovative solution to harvest microwave energy for spintronic applications, and opens the door to hybridized magnetism from artificial and natural magnetic materials for emergent applications such as efficient optospintronics, magnonic metamaterials and wireless energy transfer.

Application of Magnetic Molecular Imprinted Technology in Fluoroquinolone Antibiotics

Fluoroquinolone antibiotics (FQs) have a good bactericidal effect on a variety of bacteria, and are widely used in the treatment of various diseases. Due to the low residue and high stability in foods and water environment, it is difficult to detect FQs. Magnetic molecular imprinted technology (MIT) is specifically used for detection and identification, and magnetic molecular imprinted polymers (MIPs) are obtained by combining modified magnetic materials with polymers with specific molecular recognition cavities, which not only improves the ability to select and recognize specific template analogs, but also enables rapid separation. This review summarizes the research progress of MIPs with natural magnetic materials, magnetic nanomaterials and magnetic molecular sieve materials as carriers according to the cost, points out the advantages and current problems of each magnetic material, and describes the current status and development prospects of magnetic MIPs.

Investigation of New Zealand’s natural magnetic minerals for application in inroad charging systems

There has been a steadily increasing demand for magnetic materials in devices and charging systems over recent decades. The advent of in-road inductive power transfer (IPT) charging systems in the near future will massively increase the demand. Better, nonbrittle and affordable magnetic materials are required so that vehicles can run over charging pads built into the road without destroying them. This will require innovative solutions and new magnetic material sources to meet these needs in an economically viable way. Here, we have scoped New Zealand’s (NZ) natural magnetic materials and their ability to be included as a viable magnetic material for our roads. We have investigated the magnetic permeabilities of NZ natural magnetic mineral deposits for IPT application in roads.

The removal of arsenic from arsenic-bearing groundwater in In-situ and Ex-situ environment using novel natural magnetic rock material and synthesized magnetic material as adsorbent: A comparative assessment

The removal of arsenic from groundwater is an important issue for environmental safety and human health. Research focused on the comparative assessment of arsenic removal from arsenic-bearing groundwater and arsenic-containing-synthetic water (2 mg/L) using natural magnetic material (NMM) (rock) and synthesized magnetic material (SMM) by Bacillus pasteurii and humic acid. The arsenic-bearing groundwater (97.56 ± 0.05 μg/L) exceed the WHO limit (10 μg/L) of arsenic concentration for drinking water. The NMM contains dominantly magnetite, hematite, ferrihydrate, coesite, quartz, and stishovite. The NMM of natural rock exhibited the existence of iron (6.25–8.86% Fe3O4), which is widespread and important component in sedimentary rocks. The investigation on vibrating sample magnetometers (VSM) of NMM and SMM demonstrated the typical magnetization properties, which can be separated after arsenic removal process. The thermogravimetric analysis (TGA) of SMM displayed the existence of organic matter decomposition during particle synthesis. The TEM and SEM exhibited the nanoparticle particle formation within the range of 10–39 nm (10–20 nm particle Fe3O4 through B. pasteurii). FTIR spectrum (before and after removal of arsenic) indicated the existence and binding nature in between arsenic and iron. >90% of arsenic was removed from arsenic-bearing groundwater using Fe3O4, Fe3O4 (N2-Environment), Fe3O4 with humic acid, and Fe3O4 with B. pasteurii after 25 min, 8 min, 13 min and 120 min, respectively. In case of NMM in Site-A, the arsenic removal was observed very fast as 85–87% within 30 s, whereas 95–99%, 93–95% and 88–91% removal detected using the sample of Site-A, Site-B, and Site-C respectively, after 120 min at natural pH (8.31 ± 0.05) of arsenic-bearing groundwater. Thus, NMM, (ecofriendly green material), can be applicable for arsenic removal from arsenic-bearing groundwater.

Electric tunability of microwave permeability dispersion behaviors of metamaterials

By embedding a capacity-variable diode into a split ring resonator (SRR), it is found that the effective capacitance of such an SRR element can be varied by the biased voltage of diode. Therefore the resonance frequency and effective permeability of an SRR element can be tuned. Based on these results, a smart microwave magnetic metamaterial is proposed. Employing the finite-difference time-domain and retrieval method, the variations of resonance frequency and permeability of the SRR element are simulated and calculated by changing the biased voltage. It is found that with the decrease of capacitance due to the increase of biased voltage, the resonance frequencies are shifted towards lower values, and so are the resonance frequencies of permeability dispersion. Finally, the difference in permeability dispersion behavior between SRR structure and natural magnetic material (for instance, ferrite) has been pointed out.

Preparation of black sand-based magnetic photocatalysts for photocatalytic oxidation of aqueous phenol

A natural magnetic material, black sand, was used as cores to prepare a magnetic photocatalyst, which can be recovered using an external magnetic field. A surfactant-involved scheme was proposed to deposit a rough silica layer on the surface of black sand, which otherwise could not be coated with silica through a conventional scheme involving Stöber process. Titanium dioxide (TiO2) was deposited on the surface of the silica–black sand (Si/BS) through an impregnation process and a direct deposition process. The catalytic property of the resultant photocatalyst (Ti/Si/BS) was evaluated using the oxidation of aqueous phenol and exhibited less reactivity than Degussa P25 TiO2. The phenol removal efficiency showed a pH dependence, which was ascribed to pH effect on (a) the formation of *OH and (b) the electrostatic interaction between the photocatalyst and the substrate. The prepared photocatalyst is reusable despite slight deactivation caused by the mechanical loss of TiO2.

Focus on Magneto-Science

Magnetite, a natural magnetic material, was discovered in China several thousand years ago. Since then, many ancient people have been fascinated by the interesting properties of magnetite. Similarly, many scientists have dreamed of manipulating chemical, physical and biological phenomena using magnetic fields. Despite the long time that has passed since the discovery of magnetite, this dream has only recently been accomplished. Magnetism, an important physical property of materials, is of three types: diamagnetism, paramagnetism and ferromagnetism. The magnetic susceptibilities of diamagnetic, paramagnetic and ferromagnetic materials are in the order of -10-10, +10-8 and +10-2 m3 mol-1, respectively. Note that most commonly used materials such as water and benzene are diamagnetic; air is paramagnetic. The magnetic energy of diamagnetic and paramagnetic (magnetically weak) materials under a magnetic field of 1 T, which is the maximum field generated by a tabletop electromagnet, is very small compared with the thermal energy at room temperature. Therefore, it is difficult to believe that a magnetic field less than 1 T markedly affects the chemical and physical phenomena of magnetically weak materials. Recently, the progress of superconducting magnet manufacturing technology has enabled us to freely use strong magnetic fields of 10 T or more in our laboratories. Because magnetic energy is proportional to the square of the magnetic flux density, the magnetic energy at 10 T, for example, is 100 times greater than that at 1 T, indicating that the effect of a 10 T magnetic field on magnetically weak materials becomes so great that magnetic phenomena, which cannot be observed in a 1 T field, are very clear in a 10 T field. Consequently, many interesting phenomena have been observed. For example, it was demonstrated that water in a vessel could be separated into two parts by applying strong horizontal magnetic fields to create the so-called Moses effect. Reportedly, diamagnetic materials such as water and wood can be levitated by applying vertical magnetic fields: magnetic levitation. These phenomena are interpreted in terms of magnetic force. Although the effect of a magnetic force has been well investigated both theoretically and experimentally, before these reports it was difficult to imagine that water could be separated or levitated using magnetic fields, simply because the magnetic force generated by a tabletop electromagnet is not strong enough to demonstrate these phenomena clearly. The magnetic phenomena occurring under a 10 T field markedly differ from those under a 1 T field: strong magnetic fields of approximately 10 T present researchers with a new interdisciplinary field of science, encompassing physics, chemistry and biology, which will also be useful for technological development. Taking these benefits into account, we adopted the term 'magneto-science' (basic and applied), to refer to the investigation of magnetic field effects (MFEs) on physical, chemical and biological phenomena in order to differentiate this new interdisciplinary field from traditional ones. In consideration of the important role of magneto-science in the 21st century, this focus issue contains 16 articles selected from the International Conference on Magneto-Science (ICMS2007), which was held in Hiroshima, Japan in November 2007. The selected papers describe various studies of MFEs (? 16 T) in hard, soft and biological materials. Topics such as the magnetic processing of alloys or hard materials, spin chemistry and spin dynamics, magneto-electrochemistry, the magnetic processing of soft materials, the applications of magnetic fields to analysis, and magneto-biology are addressed to delineate the frontiers of magneto-science. We hope that this focus issue will help readers to understand several aspects of the frontiers of magneto-science.

Mössbauer, magnetic, X‐ray fluorescence and transmission electron microscopy study of natural magnetic materials from speleothems: haematite and the Morin transition

Detrital magnetic materials within cave stalagmitic formations, e.g., haematite or magnetite, carry remanence whose vector is of value in dating. Magnetometry measurements on a particular haematite‐bearing sample reveal that remanence was substantially restored and/or conserved on rewarming after cooling below the Morin transition temperature. Mossbauer measurements indicate the presence of two types of haematite, distinguished primarily by particle size. The majority is small in size, partially exhibiting superparamagnetism, and does not undergo a Morin transition above liquid nitrogen temperature. Superparamagnetic goethite is the second major component. Mine haematite samples of surface location with different color and mineralogical composition have also been studied. Possible relations between the mineralogical composition of the mine samples and detrital stalagmitic magnetic material, the modifications and the origin of this mineralization are discussed. Special attention is paid to the “irreversible” Morin transition in large enough (>20 nm) haematite particles and the possible loss of natural remanent magnetization and hence of palaeomagnetic records.

Bitter patterns versus hysteresis behavior in small single particles of hematite

To establish links among domain images, volume changes in magnetization, and mechanisms for pseudosingle‐domain (PSD) behavior, we have studied single platelets of natural hematite (Elba, Italy) in order to compare Bitter patterns resulting from high‐field treatments to the hysteresis behavior of the same individual particles. There is excellent agreement between the fields that cause large changes of a particle's Bitter pattern and the fields that cause large changes of a particle's magnetic moment. When in the saturation remanent state, most particles exhibit patterns that suggest a state of near saturation. Such patterns change very little until the application of a critical back field triggers the appearance of a major Bitter line that nearly bisects the grain. Likewise, in the majority of particles the measured ratio of saturation remanence to saturation moment is large (≅ 0.7), and there is little change in saturation remanence until a critical back field equal to the coercive force (Hc) reverses the moment through a large Barkhausen jump. In most particles whose patterns have been compared to their measured behavior, this large jump on the hysteresis loop occurs in the same critical back field that causes the sudden appearance of a major Bitter line. Consequently, we interpret hysteresis to be governed by the nucleation of walls in the majority of hematite particles studied here. In such particles, Hc increases as effective grain size decreases, according to Hc ∝ deff−0.64, where deff ∝ Ms1/3 and Ms equals the particle's saturation moment. This study leads to four conclusions: (1) Bitter patterns do represent volume domains and the magnetization processes that they imply, (2) nucleation is the dominant hysteresis mechanism in PSD particles of this natural hematite, (3) the grain size dependence of nucleation field Hn in hematite is given by Hn = Hc ∝ deff−0.64, and (4) nucleation is a viable mechanism for explaining PSD behavior in other natural magnetic materials, such as magnetite, titanomagnetite, and pyrrhotite.

A new class of natural magnetic materials: The ordering alloys

Tetrataenite (∼FeNi), found in many meteorites, and Josephinite (∼FeNi3), found in many serpentinized peridotites and possibly in Allende, a carbonaceous chondrite, are ordering alloys. Knowledge of thermomagnetic contrasts between the ordered and disordered states is of some practical importance since misinterpretation would be the consequence of failing to recognize them. Magnetic characteristics of the ordered state are recorded during heating to the apparent Curie point, which coincides with the Curie point of the disordered state. Magnetic characteristics of the disordered state are recorded during cooling from the “Curie point” to room temperature. The ordered alloys can be annealed in the vicinity of 500°C in order to monitor the kinetics of disordering, and to obtain a magnetization record characteristic of the state of order. In the ideal scenario, the minerals acquire thermoremanence (TRM) on cooling below the Curie point (∼550°C for FeNi and ∼610°C for FeNi3), and order below the ordering temperature (∼320°C for FeNi and ∼500°C for FeNi3). In natural circumstances, more likely, the appropriate alloy may form below the Curie point and above the ordering temperature and also near or below the ordering temperature. Induced magnetic anisotropy is characteristic of the ordered state, reaching the extreme for the tetragonal, truly uniaxial anisotropy in FeNi. At the present state of understanding, we can only speculate on what effect atomic ordering might have on the original remanence.