A Ferrofluid with Surface Modified Nanoparticles for Magnetic Hyperthermia and High ROS Production

A ferrofluid with 1,2-Benzenediol-coated iron oxide nanoparticles was synthesized and physicochemically analyzed. This colloidal system was prepared following the typical co-precipitation method, and superparamagnetic nanoparticles of 13.5 nm average diameter, 34 emu/g of magnetic saturation, and 285 K of blocking temperature were obtained. Additionally, the zeta potential showed a suitable colloidal stability for cancer therapy assays and the magneto-calorimetric trails determined a high power absorption density. In addition, the oxidative capability of the ferrofluid was corroborated by performing the Fenton reaction with methylene blue (MB) dissolved in water, where the ferrofluid was suitable for producing reactive oxygen species (ROS), and surprisingly a strong degradation of MB was also observed when it was combined with H2O2. The intracellular ROS production was qualitatively corroborated using the HT-29 human cell line, by detecting the fluorescent rise induced in 2,7-dichlorofluorescein diacetate. In other experiments, cell metabolic activity was measured, and no toxicity was observed, even with concentrations of up to 4 mg/mL of magnetic nanoparticles (MNPs). When the cells were treated with magnetic hyperthermia, 80% of cells were dead at 43 °C using 3 mg/mL of MNPs and applying a magnetic field of 530 kHz with 20 kA/m amplitude.

Robust ferromagnetic insulating and large exchange bias in LaMnO3:CoO composite thin films

Ferromagnetic insulators have received widespread attention for applications in novel low power consumption spintronic devices. Further optimizing the robust ferromagnetic insulating and developing multifunctional ferromagnetic insulator by integrating other magnetic property can not only ease or pave the way for actual application, but also provide an additional freedom degree for device designing. In this work, by introducing antiferromagnetic CoO into ferromagnetic insulator LaMnO3, we have constructed (1-x)LaMnO3:xCoO composite thin films. The films simultaneously show robust ferromagnetic insulator characteristics and large exchange bias. For x = 0.5 sample, the resistivity is 120 Ω·cm at 250 K while the magnetization is 100 emu/cm3 and the exchange bias field is -2200 Oe at 10 K. Especially, the blocking temperature is up to 140 K. Synchrotron radiation x-ray absorption spectroscopy reveals the coexistence of Mn3+, Mn2+, Co2+ and Co3+, arising from interfacial charge transfer and space charge/defect trapping, should be responsible for the enhanced and integrated multifunctional magnetic properties.

Using paleomagnetism to test rolling hinge behaviour of an active low angle normal fault, Papua New Guinea

<p>Metamorphic core complexes (MCC) are widespread in extensional tectonic environments. Despite their significant contribution to extension in rifts, little is known about the origin and evolution of metamorphic core complexes. Particular controversy regards the origin of the typically shallowly dipping (<30°) detachment fault that bounds the footwall core of metamorphic rocks. According to Andersonian faulting theory, normal faults should initiate at a dip of ~60° and frictionally lock up and stop slipping at dips of <30°. One possible solution to this problem is a rolling hinge evolution for the fault. In this scenario the fault initiates at a steep dip of ~60° and evolves to a shallower dip during slip due to the rebound of the footwall in response to progressive unloading as the hangingwall is removed (Wernicke & Axen, 1988; Buck, 1988; Hamilton, 1988). Large rotations of the footwall, indicative of rolling hinge style deformation, may conceivably be measured by comparing the remanent paleomagnetic vector of the footwall rocks with the expected direction of the geomagnetic field at the site where the remanent magnetization was acquired. Using these techniques, large rotations of footwall rocks consistent with rolling hinge style deformation have been demonstrated for the footwalls of oceanic core complexes (Garcés & Gee, 2006; Zhao & Tominaga, 2009; Morris et al., 2009; MacLeod et al., 2011), but not for continental MCCs. In this study we attempt to test, using the remanent magnetization of the footwall rocks, whether rolling hinge style rotations have affected the footwall of the Mai’iu fault, Papua New Guinea. The Mai’iu fault, located in the continental Woodlark Rift, is a rapidly slipping (~1 cm/yr) (Wallace et al., 2014; Webber et al., 2018), shallowly-dipping (<22° at the surface) normal fault (Spencer, 2010; Little et al., 2019) responsible for the Pliocene-Recent exhumation of the domed Suckling-Dayman MCC, which is comprised mostly of Goropu Metabasalt. The remanent magnetization of forty-four samples of footwall Goropu Metabasalt were measured for this study. Close to the fault trace (<1.5 km) a moderately inclined, northerly trending, normal component of magnetic remanence is preserved (Dec: 351.1°, Inc: -35.7°, α₉₅: 6.8°, N= 18 sites). Farther to the south, and up-dip of the fault trace (>1.5 km to 10 km from the fault trace) a normal component is observed in the lower blocking temperature range (Dec: 347.2°, Inc: -41.7°, α₉₅: 9.4°, N= 7 sites) (up to 300-400°C) that we interpret to be equivalent to the normal component present in samples closer to the fault trace. The maximum (un)blocking temperature to which the normal component is carried decreases with increasing distance up-dip and away from the fault trace. In the higher blocking temperature range a southerly trending, reversed component of magnetization is preserved that is more steeply inclined than the component mentioned above (Dec: 177.2°, Inc: 57.1°, α₉₅: 7.3°, N= 8 sites). We interpret the moderately-inclined normal component in both regions to be a recent component of magnetization to have been acquired during the exhumation of the Goropu Metabasalt over the last 780,000 years (Brunhes chron). The origin of the older, reversed component is less clear; however, we prefer the interpretation that this component is also an exhumational overprint that was acquired between 2,600,000-780,000 years ago during the Matuyama chron. Comparison of the direction of the average normal component of both Group 1 and Group 2 samples (Dec: 350.6°, Inc: -37.1°, α₉₅: 5.4°, N= 25 sites) with the expected direction of the geomagnetic field at the paleomagnetic sampling locality indicates that 23.9 ± 2.6° (1σ) of back-rotation about a sub-horizontal axis sub-parallel to fault strike has affected the footwall of the Mai’iu fault. Taking into account the known dip of the fault at the surface of <20-22°, this rotation value implies an original fault dip at depth of 41.3-48.5° that is inherited from a paleo-subduction zone. This result is remarkably consistent with other estimates of the original fault dip: for example, geologically observed fault-bedding cut-off angles on an upper plate imbricate (rider) block imply an original fault dip of ~40-49° (Little et al., 2019). Also, microseismicity between 10-25 km depth implies a modern dip there of 30-40° (Eilon et al., 2015; Abers et al., 2016). This study is the first of its kind to use paleomagnetism to demonstrate that substantial rolling hinge style rotations have affected the footwall of a continental MCC.</p>

Using paleomagnetism to test rolling hinge behaviour of an active low angle normal fault, Papua New Guinea

<p>Metamorphic core complexes (MCC) are widespread in extensional tectonic environments. Despite their significant contribution to extension in rifts, little is known about the origin and evolution of metamorphic core complexes. Particular controversy regards the origin of the typically shallowly dipping (<30°) detachment fault that bounds the footwall core of metamorphic rocks. According to Andersonian faulting theory, normal faults should initiate at a dip of ~60° and frictionally lock up and stop slipping at dips of <30°. One possible solution to this problem is a rolling hinge evolution for the fault. In this scenario the fault initiates at a steep dip of ~60° and evolves to a shallower dip during slip due to the rebound of the footwall in response to progressive unloading as the hangingwall is removed (Wernicke & Axen, 1988; Buck, 1988; Hamilton, 1988). Large rotations of the footwall, indicative of rolling hinge style deformation, may conceivably be measured by comparing the remanent paleomagnetic vector of the footwall rocks with the expected direction of the geomagnetic field at the site where the remanent magnetization was acquired. Using these techniques, large rotations of footwall rocks consistent with rolling hinge style deformation have been demonstrated for the footwalls of oceanic core complexes (Garcés & Gee, 2006; Zhao & Tominaga, 2009; Morris et al., 2009; MacLeod et al., 2011), but not for continental MCCs. In this study we attempt to test, using the remanent magnetization of the footwall rocks, whether rolling hinge style rotations have affected the footwall of the Mai’iu fault, Papua New Guinea. The Mai’iu fault, located in the continental Woodlark Rift, is a rapidly slipping (~1 cm/yr) (Wallace et al., 2014; Webber et al., 2018), shallowly-dipping (<22° at the surface) normal fault (Spencer, 2010; Little et al., 2019) responsible for the Pliocene-Recent exhumation of the domed Suckling-Dayman MCC, which is comprised mostly of Goropu Metabasalt. The remanent magnetization of forty-four samples of footwall Goropu Metabasalt were measured for this study. Close to the fault trace (<1.5 km) a moderately inclined, northerly trending, normal component of magnetic remanence is preserved (Dec: 351.1°, Inc: -35.7°, α₉₅: 6.8°, N= 18 sites). Farther to the south, and up-dip of the fault trace (>1.5 km to 10 km from the fault trace) a normal component is observed in the lower blocking temperature range (Dec: 347.2°, Inc: -41.7°, α₉₅: 9.4°, N= 7 sites) (up to 300-400°C) that we interpret to be equivalent to the normal component present in samples closer to the fault trace. The maximum (un)blocking temperature to which the normal component is carried decreases with increasing distance up-dip and away from the fault trace. In the higher blocking temperature range a southerly trending, reversed component of magnetization is preserved that is more steeply inclined than the component mentioned above (Dec: 177.2°, Inc: 57.1°, α₉₅: 7.3°, N= 8 sites). We interpret the moderately-inclined normal component in both regions to be a recent component of magnetization to have been acquired during the exhumation of the Goropu Metabasalt over the last 780,000 years (Brunhes chron). The origin of the older, reversed component is less clear; however, we prefer the interpretation that this component is also an exhumational overprint that was acquired between 2,600,000-780,000 years ago during the Matuyama chron. Comparison of the direction of the average normal component of both Group 1 and Group 2 samples (Dec: 350.6°, Inc: -37.1°, α₉₅: 5.4°, N= 25 sites) with the expected direction of the geomagnetic field at the paleomagnetic sampling locality indicates that 23.9 ± 2.6° (1σ) of back-rotation about a sub-horizontal axis sub-parallel to fault strike has affected the footwall of the Mai’iu fault. Taking into account the known dip of the fault at the surface of <20-22°, this rotation value implies an original fault dip at depth of 41.3-48.5° that is inherited from a paleo-subduction zone. This result is remarkably consistent with other estimates of the original fault dip: for example, geologically observed fault-bedding cut-off angles on an upper plate imbricate (rider) block imply an original fault dip of ~40-49° (Little et al., 2019). Also, microseismicity between 10-25 km depth implies a modern dip there of 30-40° (Eilon et al., 2015; Abers et al., 2016). This study is the first of its kind to use paleomagnetism to demonstrate that substantial rolling hinge style rotations have affected the footwall of a continental MCC.</p>

Magnetic properties of iron oxide nanoparticles with a DMSA-modified surface

The magnetic properties of magnetite nanoparticles (Fe3O4 NPs) strongly depend on their chemical and physical parameters, which can be regulated by a controlled synthesis process. To improve the quality of the obtained nanoparticles, their surface is often modified with organic compounds (from the group of surfactants, sugars, proteins, or organic acid). In this study, we synthesized magnetite nanoparticles with a surface modified with the organic compound DMSA. Then, the nanocrystallites were characterized in terms of structure and morphology. To investigate the role of DMSA and to understand the adsorption mechanism, FTIR measurements were carried out. Using Mössbauer spectroscopy, we investigated temperature-induced changes in the magnetic properties of prepared samples. The spectra were recorded in a wide temperature range (from 4 K to 390 K) for two types of samples: powders and ferrofluids with various concentrations. In the case of powder samples, the superparamagnetic doublet appeared at room temperature. For magnetic suspensions, the spectra were more complicated. They consisted of superposition of asymmetrically broadened sextets and doublets, which was caused by the occurrence of long-range dipole-dipole interactions. These interactions affected the magnetic properties of the material and increased the blocking temperature. Additionally, the magnetic hysteresis and zero field cooling-field cooling (ZFC/FC) curves were measured with the use of a vibrating sample magnetometer.

An Archaeomagnetic Study of Hangi Stones in New Zealand

<p>Burnt or fired archaeological artefacts often retain a record of the magnetic field in which they were last heated and cooled. Over the past four years we have collected oriented hangi stones from 10 archaeological sites spread across the North and South Islands of New Zealand. The stones vary in lithology from andesites, originating from the central North Island volcanoes, favoured by Maori for their durability and with remanent magnetization up to 30 A/m, to sandstones and schists from the main axial ranges, with magnetizations as weak as 10-4 A/m. Radiocarbon dating of charcoal fragments retrieved from amongst the stones indicates that the sites span from ca. 1400 AD to the present. In all cases, we have independently oriented and retrieved several stones, and we have made several samples from each stone, either by drilling (standard cylindrical samples) or sawing (pseudo-cubes) in the laboratory. We have calculated site mean palaeomagnetic directions (Dec between 1.5o and 19.6o and Inc between -52.2o and -68.3o) from principal component analysis of thermal demagnetization and alternating field demagnetization data, discarding the data of stones that show evidence of disturbance after cooling. The directions are in good agreement with recently published palaeosecular variation records from lake sediments. We have carried out palaeointensity experiments using the Coe/Thellier method with pTRM and tail checks, and with selection criteria modified to the situation. Palaeointensities range from 50μT to 77μT. Rock magnetic experiments contribute to our understanding of the mineralogy, domain state and blocking temperature spectra. We compare our data with predictions of the global field models ARCH3k and gufm1, and suggest that the addition of our new data will improve these models for the SW Pacific region for the most recent time period. Archaeomagnetic measurements are also used to date hangi sites by matching the palaeo-direction to an established archaeomagnetic dating model, NZPSV1k. Archaeomagnetic dating is used to resolve ambiguities in the calibration of radiocarbon dates, and shows up inconsistencies due to unreliable source material for radiocarbon dating. Archaeomagnetic dating and radiocarbon dating results are combined to give the best estimates of the best age of the hangi sites.</p>

An Archaeomagnetic Study of Hangi Stones in New Zealand

<p>Burnt or fired archaeological artefacts often retain a record of the magnetic field in which they were last heated and cooled. Over the past four years we have collected oriented hangi stones from 10 archaeological sites spread across the North and South Islands of New Zealand. The stones vary in lithology from andesites, originating from the central North Island volcanoes, favoured by Maori for their durability and with remanent magnetization up to 30 A/m, to sandstones and schists from the main axial ranges, with magnetizations as weak as 10-4 A/m. Radiocarbon dating of charcoal fragments retrieved from amongst the stones indicates that the sites span from ca. 1400 AD to the present. In all cases, we have independently oriented and retrieved several stones, and we have made several samples from each stone, either by drilling (standard cylindrical samples) or sawing (pseudo-cubes) in the laboratory. We have calculated site mean palaeomagnetic directions (Dec between 1.5o and 19.6o and Inc between -52.2o and -68.3o) from principal component analysis of thermal demagnetization and alternating field demagnetization data, discarding the data of stones that show evidence of disturbance after cooling. The directions are in good agreement with recently published palaeosecular variation records from lake sediments. We have carried out palaeointensity experiments using the Coe/Thellier method with pTRM and tail checks, and with selection criteria modified to the situation. Palaeointensities range from 50μT to 77μT. Rock magnetic experiments contribute to our understanding of the mineralogy, domain state and blocking temperature spectra. We compare our data with predictions of the global field models ARCH3k and gufm1, and suggest that the addition of our new data will improve these models for the SW Pacific region for the most recent time period. Archaeomagnetic measurements are also used to date hangi sites by matching the palaeo-direction to an established archaeomagnetic dating model, NZPSV1k. Archaeomagnetic dating is used to resolve ambiguities in the calibration of radiocarbon dates, and shows up inconsistencies due to unreliable source material for radiocarbon dating. Archaeomagnetic dating and radiocarbon dating results are combined to give the best estimates of the best age of the hangi sites.</p>

Magnetic properties of a fullerene-like X20 structure with embedded metal atom

Monte Carlo simulation has been used to study magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1, 3/2) Ising fullerene-like X20 structure with embedded metal atom. Under the influence of the anisotropy and the concentration of surface shell atom, the system tends to show the multiple stable saturation values of magnetization (M=0.91, 0.85, 0.77, 0.64, 0.50 and 0.023) and the values of intermediate metastable magnetization (M=0.88, 0.76 and 0.60) at zero temperature. The blocking temperature TB becomes higher by decreasing the anisotropies (|DC |, |DS |), or increasing the exchange coupling |JCS |, the magnetic field h and the concentration of surface shell atom PS . Some interesting phenomena have been found such as the double-loop hysteresis behavior for the relatively large values of |DS | (≥2.0), originating from the competition between different physical parameters.

Magnetic Study of CuFe2O4-SiO2 Aerogel and Xerogel Nanocomposites

CuFe2O4 is an example of ferrites whose physico-chemical properties can vary greatly at the nanoscale. Here, sol-gel techniques are used to produce CuFe2O4-SiO2 nanocomposites where copper ferrite nanocrystals are grown within a porous dielectric silica matrix. Nanocomposites in the form of both xerogels and aerogels with variable loadings of copper ferrite (5 wt%, 10 wt% and 15 wt%) were synthesized. Transmission electron microscopy and X-ray diffraction investigations showed the occurrence of CuFe2O4 nanoparticles with average crystal size ranging from a few nanometers up to around 9 nm, homogeneously distributed within the porous silica matrix, after thermal treatment of the samples at 900 °C. Evidence of some impurities of CuO and -Fe2O3 was found in the aerogel samples with 10 wt% and 15 wt% loading. DC magnetometry was used to investigate the magnetic properties of these nanocomposites, as a function of the loading of copper ferrite and of the porosity characteristics. All the nanocomposites show a blocking temperature lower than RT and soft magnetic features at low temperature. The observed magnetic parameters are interpreted taking into account the occurrence of size and interaction effects in an ensemble of superparamagnetic nanoparticles distributed in a matrix. These results highlight how aerogel and xerogel matrices give rise to nanocomposites with different magnetic features and how the spatial distribution of the nanophase in the matrices modifies the final magnetic properties with respect to the case of conventional unsupported nanoparticles.