Evidence for weak ferromagnetic moment within the basal plane of hematite natural crystals at low temperature

Lowerature magnetization of hematite within the basal plane has been studied in a collection of natural crystals by means of torque magnetometry. Comparison between the torque curves at room temperature and at 77 K allows identification of a weak ferromagnetic moment constrained within the basal plane at temperatures well below the Morin transition. Annealing the samples produces the expected reduction of the weak ferromagnetic moment, but there is also a relationship between the ferromagnetic moment before and after annealing. Lowerature measurements after the annealing experiment reveal the presence of a weak ferromagnetic moment that survives the annealing. This observation suggests the magnetic structure of natural hematite crystals below the Morin transition can still be a carrier of magnetization. Key Points A weak ferromagnetic (WFM) moment is detected below the Morin transition The WFM lies within the basal plane Natural Hematite is not a pure AF below TM ©2013. American Geophysical Union. All Rights Reserved.Peer Reviewe

Searching for magnetic monopoles trapped in accelerator material at the Large Hadron Collider

If produced in high energy particle collisions at the LHC, magnetic monopoles could stop in material surrounding the interaction points. Obsolete parts of the beam pipe near the CMS interaction region, which were exposed to the products of pp and heavy ion collisions, were analysed using a SQUID-based magnetometer. The purpose of this work is to quantify the performance of the magnetometer in the context of a monopole search using a small set of samples of accelerator material ahead of the 2013 shutdown.Comment: 11 page

Effects of Hybrid Flow Control on a Normal Shock Boundary-Layer Interaction

Hybrid flow control, a combination of micro-ramps and steady micro-jets, was experimentally investigated in the 15x15 cm Supersonic Wind Tunnel at the NASA Glenn Research Center. A central composite design of experiments method, was used to develop response surfaces for boundary-layer thickness and reversed-flow thickness, with factor variables of inter-ramp spacing, ramp height and chord length, and flow injection ratio. Boundary-layer measurements and wall static pressure data were used to understand flow separation characteristics. A limited number of profiles were measured in the corners of the tunnel to aid in understanding the three-dimensional characteristics of the flowfield

Experimental Investigation of Normal Shock Boundary-Layer Interaction with Hybrid Flow Control

Hybrid flow control, a combination of micro-ramps and micro-jets, was experimentally investigated in the 15x15 cm Supersonic Wind Tunnel (SWT) at the NASA Glenn Research Center. Full factorial, a design of experiments (DOE) method, was used to develop a test matrix with variables such as inter-ramp spacing, ramp height and chord length, and micro-jet injection flow ratio. A total of 17 configurations were tested with various parameters to meet the DOE criteria. In addition to boundary-layer measurements, oil flow visualization was used to qualitatively understand shock induced flow separation characteristics. The flow visualization showed the normal shock location, size of the separation, path of the downstream moving counter-rotating vortices, and corner flow effects. The results show that hybrid flow control demonstrates promise in reducing the size of shock boundary-layer interactions and resulting flow separation by means of energizing the boundary layer

New directional archeomagnetic data of burned cave sediments from Switzerland and geomagnetic field variations in Central Europe

This paper presents new directional archeomagnetic data from nine Meso-/Neolithic fireplaces, sampled in a cave shelter, at Arconciel, in western Switzerland. Rock magnetic measurements indicate a homogenous magnetic mineralogy in all fireplaces, with magnetite as the main magnetic carrier. The remanent magnetization is stable and generally shows one characteristic directional component. Nine new directions, which were obtained from Arconciel, are combined with 356 other archeomagnetic data from a circular area with a radius of 700km around this site, to obtain a penalized least square spline fit for the past 9000yr. We found in general good agreement with other local compilations, such as the Balkan curve, the regional SCHA.DIF.8k model and with lake sediments from UK, Fennoscandia and Switzerland. Nevertheless, a time lag of several centuries is observed for a declination maximum between the archeomagnetic spline fit and the other European data records around 5900BC. This time lag is also observed in the Swiss lake sediment record; therefore we interpret this shift as a local feature of the Earth's magnetic fiel

Crystallographic—magnetic correlations in single-crystal haemo-ilmenite: new evidence for lamellar magnetism

17 single crystals were identified by electron backscatter diffraction (EBSD) and isolated from coarse massive haemo-ilmenite ore from South Rogaland, Norway. These were studied using the EBSD results, natural remanent magnetization (NRM), and anisotropy of magnetic susceptibility (AMS), to gain a better understanding of angular relationships between crystallographic axes and magnetic properties of haemo-ilmenite in relation to lamellar magnetism. Electron microprobe analyses gave the following average end-member compositions for ilmenite host: 21.1 per cent MgTiO3, 73.7 FeTiO3, 0.5 MnTiO3, 4.3 Fe2O3, 0.2 Cr2O3 and 0.3 V2O3; and for the coarsest (∼3 μm) haematite exsolution lamellae: 3.5 MgTiO3, 22.4 FeTiO3, 71.4 Fe2O3, 1.6 Cr2O3, 1.0 V2O3 and 0.1 Al2O3, making this sample the most Mg- and Cr-rich haemo-ilmenite studied in the province, but with similar element fractionations between the coexisting phases. TEM work on similar material suggests the presence of much thinner exsolution down to 1-2 nm. The EBSD, NRM and AMS results from 12 out of 17 crystals indicate a good agreement between the orientation of crystallographic axes, NRM direction and principal axes of the magnetic susceptibility ellipsoid, with the NRM located in the (0001) basal plane [NRM ∧ (0001) < 6.5°] and the crystallographic c axis quasi-parallel to the minimum axis of the susceptibility ellipsoid [c∧ k3 < 13.5°]. In addition, in 10 of these 12 crystals, the remanent magnetization vector is parallel or nearly parallel to the positive direction of a crystallographic a axis [NRM ∧a < 20°], hence parallel to a principal magnetic moment direction in haematite as determined by Besser, and not parallel to the spin-canted direction of end-member haematite. This is consistent with a basic property of lamellar magnetism, where the magnetic moment is parallel to the principal moments (sublattice magnetization directions) in haematite. Relationships in three additional crystals with NRM ∧a= 22°-33°, only two with good agreement, can be interpreted as consistent with having a magnetic vector quasi-parallel to the spin-canted direction of haematit