Paleomagnetic and rock magnetic properties of ODP Leg 173 sites, west Iberia continental margin

We present detailed paleomagnetic and rock magnetic results of rock samples recovered during Leg 173. The Leg 173 cores display a multicomponent magnetization nature. Variations in magnetic properties correlate with changes in lithology that result from differences in the abundance and size of magnetic minerals. The combined investigation suggests that the magnetic properties of the "fresher" peridotite samples from Site 1070 are controlled mainly by titanomagnetite, with a strong Verwey transition in the vicinity of 110 K, and with field- and frequency-dependent susceptibility curves that resemble those of titanomagnetites. These results are in excellent agreement with thermomagnetic characteristics where titanomagnetites with Curie temperature ~580°C were identified from the "fresher" peridotites. In contrast to the magnetic properties observed from the "fresher" peridotites, the low-temperature curves for the "altered" peridotites did not show any Verwey transition. Thermomagnetic analysis using the high-temperature vibrating sample magnetometer also failed to show evidence for titanomagnetites. The remanent magnetization is carried by a thermally unstable mineral that breaks down at ~420°C, probably maghemite. The field- and frequency-dependent relationships are also directly opposite to those in the reversal zone, with no signs of titanomagnetite characteristics. Altogether, these rock magnetic data seem to be sensitive indicators of alteration and support the contention that maghemite is responsible for the magnetic signatures displayed in the altered peridotites of the upper section. The magnetic minerals of the basement rocks from Sites 1068, 1069, and 1070 are of variable particle size but fall within the pseudo-single-domain size range (0.2-14 µm). The average natural remanent magnetization (NRM) intensity of recovered serpenitinized peridotite is typically on the order of 20 mA/m for samples from Site 1068, but ~120 mA/m for samples from Site 1070. The much stronger magnetization intensity of Site 1070 is apparently in excellent agreement with the observed magnetic anomaly high. Nearly half of the NRM intensity remained after 400°C demagnetization, suggesting that the remanence can contribute significantly to the marine magnetic anomaly.

Rock magnetism of pelagic sediments from DSDP Leg 85 sites

A detailed rock magnetic investigation has been carried out on Deep Sea Drilling Project (DSDP) pelagic sediments from the Central Equatorial Pacific. This comprises hysteresis and thermomagnetic measurements, Lowrie-Fuller test and, for the first time, ferromagnetic resonance (FMR). Nearly stochiometric magnetite in two grain size fractions, single domain (SD) and multi domain (MD), has been deduced to be the carrier of magnetic remanence. Comparatively strong paramagnetic contributions are carried by pyrite, being identified by X-ray analysis. The statistical analysis of paleomagnetic parameters (NRM, MDF, initial susceptibility, Königsberger ratio Q) from a large number (> 1000) of samples, supported by hysteresis measurements, indicates a latitude and sedimentation rate dependent ratio of SD/MD grains. Possible sources for the magnetic constituents are discussed in terms of bacterial, volcanic, meteoritic and authigenic origin.

Magnetic state of ocean basalts (Table 1)

The natural remanent magnetization (NRM) of ocean basalts, giving rise to the pattern of marine magnetic anomalies, is known to be of comparatively low intensity for about 20 Ma old oceanic crust. The aim of this study is to detect possible peculiarities in the rock magnetic properties of ocean basalts of this age, and to establish a link between magnetomineralogy, rock magnetic parameters, and the low NRM intensity. Ocean basalts covering ages from 0.7 to 135 Ma were selected for rock magnetic experiments and their room temperature hysteresis parameters, Curie temperature and temperature dependence of saturation magnetization MS(T) was determined and complemented by reflected light microscopy. The majority of samples is magnetically dominated by titanomagnetite and titanomaghemite with increasing oxidation state with age. For these, a strong dependence of hysteresis parameters on the age of the samples is found. The samples have a minimum in saturation magnetization and a maximum in magnetic stability in the age interval ranging from approximately 10 to 40 Ma, coinciding with the age interval of low NRM intensity. The observed change in saturation magnetization is in the same order as that for the NRM intensity. A further peculiarity of the titanomaghemites from this age interval is the shape of their MS(T) curves, which display a maximum above room temperature (Neel P-type) and, sometimes, a self-reversal of magnetization below room temperature (Neel N-type). These special rock magnetic properties can be explained by titanomagnetite low-temperature oxidation and highly oxidized titanomaghemites in the age interval 10-40 Ma. A corresponding measurement of the NRM at elevated temperature allows to identify a maximum in NRM intensity above room temperature for the samples in that age interval. This provides evidence that the NRM is equally carried by titanomaghemites and that the low NRM intensities for about 20 Ma old ocean basalts are caused consequently by the low saturation magnetization of these titanomaghemites.

(Table 1) Magnetic properties and Curie temperatures of basalts from DSDP Leg 65 holes

During DSDP Leg 65, we achieved significant basement penetration at three sites (482, 483, and 485) in the mouth of the Gulf of California (Lewis and Robinson, 1983, doi:10.2973/dsdp.proc.65.1983). Since these holes were all drilled into extremely young crust near the crest of the East Pacific Rise, the rocks we recovered present an unusual opportunity to study the magnetic properties of submarine basalts before alteration has become pervasive. To take advantage of this opportunity and to complement the paleomagnetic studies conducted on these basalts by Day (1983, doi:10.2973/dsdp.proc.65.138.1983), we have studied, in the same samples, the following properties: saturation magnetization (Js); intensity and stability of isothermal remanent magnetization (IRM); hysteresis parameters, such as the coercive force (Hc), the remanent coercive force (HRC), and the ratio of saturation remanence (JRS) to saturation magnetization; susceptibility (x); and Curie temperature (Tc). In this chapter we will discuss the results of these studies in conjunction with the opaque mineralogy of the samples.

Síntese e caracterização estrutural, magnética e térmica da hidroxiapatita dopada com ferro

In this work, composites were prepared using high energy mechanical milling from the precursors hydroxyapatite - HAp (Ca10(PO4)6(OH)2) and metallic iron ( -Fe ). The main goal here is to study composites in order to employ them in magnetic hyperthermia for cancer therapy. The produced samples were characterized by X-ray di raction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), magnetization curves as a function of applied eld (MxH), and nally measurements of magnetic hyperthermia. The XRD patterns of the milled samples HAp/Fe revealed only the presence of precursor materials. The SEM showed clusters with irregular shapes. The magnetization curves indicated typical cases of weak ferromagnetic behavior. For samples submitted to grinding and annealing, the identi ed phases were: HAp (Ca10(PO4)6(OH)2), hematite (Fe2O3) and Calcium Iron Phosphate (Ca9Fe(PO4)7). Analyzing the results of MxH, there was a reduction of the saturation magnetization, given that the Fe was incorporated into HAp. Hysteresis curves obtained at 300 K are characteristics of samples possessing over a phase. At 77 K, the behavior of the hysteresis curve is in uenced by the presence of hematite, which is antiferromagnetic. Already at T = 4.2 K, it is observed a weak ferromagnetic behavior. Furthermore, there is the e ect of exchange bias. Regarding the magnetic hyperthermia, the results of temperature measurements as a function of the alternating eld are promising for applications in magnetic hyperthermia and other biomedical applications.

Estudo da densidade de corrente crítica para reversão da magnetização de nanoelementos ferromagnéticos

The discovery that a spin-polarized current is capable of exerting a torque in a ferromagnetic material, through spin transfer, might provide the development of new technological devices that store information via the direction of magnetization. The reduction of current density to revert the magnetization is a primary issue to potential applications on non volatile random access memories (MRAM). We report a theorical study of the dipolar and shape effects on the critical current density for reversal of magnetization, via spin transfer torque (STT), on ferromagnetic nanoelements. The nanostructured system consists on a reference layer, in which the current will be spin-polarized, and a free layer of magnetization reversal. We observed considerable changes on the critical current density as a function of the element’s reversion layer thickness (t = 1.0 nm, 1.5 nm, 2.0 nm e 2.5 nm) and geometry (circular and elliptical), the material kind of the system free layer (Iron and Permalloy) and according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced about 50% by reducing the Fe free layer thickness and around 75% when we change the saturation magnetization of circular nanoelements with 2.5 nm of thickness. We still observed a reduction as much as 90% on the current density of reversion for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.