[1] We describe a modification to existing algorithms for the calculation of first-order reversal curve (FORC) diagrams using locally weighted regression smoothing (often referred to as ''LOESS'' smoothing). The new algorithm offers several advantages over current methods: (1) it allows the FORC distribution to be calculated using a constant smoothing factor all the way to the H c = 0 axis; (2) noninteger values of the smoothing factor can be specified, enabling finer control over the degree of smoothing and the development of a graphical method for automated selection of the optimum smoothing factor; (3) it performs automated extrapolation across gaps or undefined regions of FORC space. This has two applications: first, bad curves or outlying data points caused by instrumental instabilities can be removed from the data, eliminating artifacts from the final FORC diagram; second, specific regions of interest in the FORC measurement can be masked out in order to investigate their contribution to the final FORC diagram. The new algorithm forms the basis of FORCinel, a new user-friendly suite of FORC analysis tools with graphical user interface.Components: 4918 words, 8 figures.

24 25 26Accepted Manuscript. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/.2 Magnetic fields are proposed to have played a critical role in some of the most enigmatic 26 processes of planetary formation by mediating the rapid accretion of disk material onto the 27 central star and the formation of the first solids. However, there have been no direct 28 experimental constraints on these fields. Here we show that dusty olivine-bearing 29 chondrules from the Semarkona meteorite were magnetized in a nebular field of 54±21 µT. 30This intensity supports chondrule formation by nebular shocks or planetesimal collisions 31 rather than by electric currents, the x-wind, or other mechanisms near the sun. This 32 implies that background magnetic fields in the terrestrial planet-forming region were likely 33 5-54 µT, which is sufficient to account for measured rates of mass and angular momentum 34 transport in protoplanetary disks. 35 36Astronomical observations of young stellar objects indicate that early planetary systems 37 evolve through a protoplanetary disk phase in <5 million years (My) following the collapse of 38 their parent molecular clouds (1, 2). Disk evolution on such short timescales requires highly 39 efficient inward transport of mass accompanied by outward angular momentum transfer, which 40 allows disk material to accrete onto the central star while delivering angular momentum out of 41 the protoplanetary system. 42The mechanism of this rapid mass and angular momentum redistribution remains unknown. 43Several proposed processes invoke a central role for nebular magnetic fields. Among these, the 44 magnetorotational instability (MRI) and magnetic braking predict magnetic fields with intensities 45 of ~100 µT at 1 AU in the active layers of the disk (3, 4). Alternatively, transport by 46 magnetocentrifugal wind (MCW) requires large-scale, ordered magnetic fields stronger than ~10 47 µT at 1 AU. Finally, non-magnetic effects such as the baroclinic and Goldreich-Schubert-Fricke 48 instabilities may be the dominant mechanism of angular momentum transport in the absence of 49 sufficiently strong magnetic fields (5). Direct measurement of magnetic fields in the planet-50 forming regions of the disk can potentially distinguish among and constrain these hypothesized 51 mechanisms. 52Although current astronomical observations cannot directly measure magnetic fields in 53 planet-forming regions [(6); supplementary text], paleomagnetic experiments on meteoritic 54 materials can potentially constrain the strength of nebular magnetic fields. Chondrules are 55 millimeter-sized lithic constituents of primitive meteorites that formed in transient heating events 56 in the solar nebula. If a stable field was present during cooling, they should have acquired a 57 thermoremanent magnetization (TRM), which can be characterized via paleomagnetic 58 experiments. Besides assessing the role of magnetic fields in disk evolution, such paleomagnetic 59 measure...

Magnetic anomalies associated with slowly cooled igneous and metamorphic rocks are commonly attributed to the presence of the mineral magnetite. Although the intermediate members of the ilmenite-haematite mineral series can also carry a strong ferrimagnetic remanence, it is preserved only in rapidly cooled volcanic rocks, where formation of intergrowths of weakly magnetic haematite and paramagnetic ilmenite is suppressed. But the occurrence of unusually large and stable magnetic remanence in rocks containing such intergrowths has been known for decades, and has recently been the subject of intense investigation. These unmixed oxide phases have been shown to contain pervasive exsolution lamellae with thickness from 100 microm down to about 1 nm (one unit cell). These rocks, many of which contain only a few per cent of such oxides, show natural remanent magnetizations up to 30 A m(-1) --too strong to be explained even by pure haematite in an unsaturated state. Here we propose a new ferrimagnetic substructure created by ferrous-ferric 'contact layers' that reduce charge imbalance along lamellar contacts between antiferromagnetic haematite and paramagnetic ilmenite. We estimate that such a lamellar magnetic material can have a saturation magnetization up to 55 kA m(-1) --22 times stronger than pure haematite-- while retaining the high coercivity and thermal properties of single-domain haematite.

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Paleomagnetic measurements of meteorites 1-5 suggest that, shortly after the birth of the solar system, the molten metallic cores of many small planetary bodies convected vigorously and were capable of generating magnetic fields 6 . Convection on these bodies is currently thought to have been thermally driven 7,8 , implying that magnetic activity would have been short-lived 9 . Here we present a time-series paleomagnetic record of the field recorded by the Imilac and Esquel pallasite meteorites, derived from nanomagnetic images 10 of their metallic matrices. The results reveal a history of long-lived magnetic activity on the pallasite parent body, capturing the decay and eventual shut down of the magnetic field. We demonstrate that magnetic activity driven by progressive solidification of an inner core 11-13 is consistent with our measured magnetic field characteristics and cooling rates 14 . Solidification-driven convection was likely common among small body cores 15 , and, in contrast to thermally driven convection, will have led to a relatively late (hundreds of millions of years after accretion), long-lasting, intense and widespread epoch of magnetic activity among these bodies in the early solar system.The pallasites are slowly cooled (2 -9 K Myr -1 ) 14 stony-iron meteorites 16 , which originated from the mid-to upper-mantle of a ~200-km-radius body 1 . The slow cooling rate of these meteorites allowed for characteristic microstructures to form in their metal matrix 17 , a key feature of which are regions of intergrown nanoscale islands of tetrataenite (ordered FeNi) 18,19 and an ordered Fe 3 Ni matrix 20 , collectively known as cloudy zones (CZ) 21 . During parent body cooling, these tetrataenite islands exsolved and subsequently coarsened over tens of millions of years 22 . The island diameter decreases systematically across the CZ, reflecting a decrease in the local formation age of the islands 20 . Each island adopted one of three orthogonal magnetic easy axes as it formed 18,23 , thus could display any one of six magnetisation directions. Variations in the intensity and direction of an external magnetic field led to measurable differences in the populations of each magnetisation direction 20 . Crucially, the temporal evolution of an external field is recorded by the variations in the relative proportions of these directions across the CZ 10 , which can be quantified using high-resolution nanomagnetic imaging. These images were captured for the Imilac and Esquel pallasites, utilising X-ray magnetic circular dichroism 24,25 at the X-ray photoemission electron microscope (XPEEM) 26 at the BESSY II synchrotron, Berlin, which provides the spatially resolved magnetisation of a sample surface with a resolution down to 40 nm over a 5 µm field-of-view 10 .Four and six non-overlapping, 450-nm-wide regions across the CZ (decreasing age) were extracted from the XPEEM images of Imilac and Esquel meteorites, respectively (Fig. 1). The field recorded by each region was deduced by comparing the experimental XPEEM sig...