Superconducting Quantum Interference Device Magnetometry Research Articles

Surfactant modified MgFe2O4 nanopowders by reverse micelle processing: Effect of water to surfactant ratio (R) on the particle size and magnetic property

Nanoparticles of surfactant modified MgFe2O4 have been synthesized by reverse micelle processing using tertiary system of heptane/Igepal CO 520/H2O. The effect of water to surfactant ratio on the particle size and magnetic property has been studied. X-ray diffraction analysis confirms that MgFe2O4 nanoparticles are crystalline in nature with cubic spinel structure. The average particle size increases with increase in water to surfactant ratio. The Fourier transform infrared (FTIR) analysis confirms that the surface of MgFe2O4 nanoparticles was coated with surfactants. The saturation magnetization ranged from 14.4 to 40.05emu/g was measured by Superconducting Quantum Interference Device Magnetometry (SQUID).

Determination of the Temperature Dependence of the Magnetic Anisotropy Constant in Magnetite Nanoparticles

The temperature dependence of the effective magnetic anisotropy constant, K(T ), of Fe3O4 (magnetite) nanoparticles is obtained based on SQUID (superconducting quantum interference device) magnetometry. The variation of the blocking temperature, TB , as a function of particle radius, r, is first determined by associating the particle size distribution and the anisotropy energy barrier distribution deduced from the hysteresis curve and from the magnetization decay curve, respectively. Finally, the magnetic anisotropy constant at each temperature is calculated from the relation between r and TB . The resultant effective magnetic anisotropy constant K(T ) decreases markedly with increasing temperature from 5.9 × 10 J/m at 5 K to 1.1 × 10 J/m at 280 K.

Electric Current Imaging by Ultrasonography and SQUID Magnetometry

In this paper, we propose a new method for imaging the distribution of electric currents; this method involves a combination of ultrasonography and SQUID magnetometry. To evaluate this new method, we used a block of gelatin pierced through by a lead wire as a model of a biological object. An electric current was applied to the wire and the magnetic signal generated around the wire was measured by a superconducting quantum interference device (SQUID). At the same time, an ultrasound image of the wire was taken by means of an ultrasound imaging machine. Subsequently, the magnetic field image was aligned with the ultrasound image with respect to the position of marker coils relative to the ultrasound probe. The source of the magnetic signal was localized by solving the inverse problem and visualized on the ultrasound image of the wire. The position error was 2.9 mm. The results demonstrated the applicability of the new technique combining SQUID magnetometry with ultrasound imaging.

Sensitive SQUID magnetometry for studying nanomagnetism

The superconducting quantum interference device (SQUID) magnetometer is one of the most sensitive experimental techniques to magnetically characterize samples with high sensitivity. Here we present a detailed discussion of possible artifacts and pitfalls characteristic for commercial SQUID magnetometers. This includes intrinsic artifacts which stem from the inherent design of the magnetometer as well as potential issues due to the user. We provide some guidelines on how to avoid and correct these, which is of particular importance when the proper magnetization of nanoscale objects will be established in cases where its response is dwarfed by that of the substrate it comes with, a situation frequently found in the field of nanomagnetism.

Magnetic properties and cation ordering in two synthetic bornite samples, Cu5(Fe,Mn)S4

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 113-121 - DOI: 10.2451/2011PM0009 Special Issue in memory of Sergio Lucchesi Magnetic properties and cation ordering in two synthetic bornite samples, Cu 5 (Fe, Mn)S 4 Miria Borgheresi 1 , Francesco Di Benedetto 2,* , Andrea Caneschi 2, Maurizio Romanelli 2 and David J.Vaughan 3 1 Via Matteotti 27, Pontassieve, Firenze, Italy 2 Dipartimento di Chimica, Universita di Firenze, Sesto Fiorentino, Firenze, Italy 3 Williamson Research Centre for Molecular Environmental Science, and School of Earth, Atmospheric and Environmental Sciences, University of Manchester, UK *Corresponding author: francesco.dibenedetto@unifi.it Abstract The magnetic properties of a synthetic bornite, Cu 5 FeS 4 , and of a Mn-bearing synthetic bornite were investigated using Superconducting Quantum Interference Device (SQUID) magnetometry and room temperature X-band Electron Paramagnetic Resonance (EPR) spectroscopy. Samples were synthesised from the elements using conventional dry methods. Chemical and phase compositions of the samples were confirmed by means of Electron Probe Micro-Analysis (EPMA) and by powder X-Ray Diffraction (XRD). Experimental results, interpreted using spectral simulations, highlight the superexchange nature of ionic interactions between paramagnetic centres and the role played by partial intervalence charge transfer between the Fe(III) and Cu(I) species in natural and synthetic bornite. The cation distribution in synthetic samples was shown to be different from the natural sample, in spite of the close similarity in chemical composition and structure. Key words : bornite; intervalence charge transfer; EPR spectroscopy; SQUID magnetometry; EPMA; Mn(II).

On the incorporation of beryllium into the biotemplated synthesis ofYBa2Cu3O7−δ

This work represents the first SQUID (superconducting quantuminterference device) magnetometry study on the effect of incorporatingberyllium into the synthesis of the high temperature superconductorYBa2Cu3O7−δ (Y123). Through a biopolymer-mediated synthetic approach, the homogeneous nature ofthe precursor sol and the preferred nucleation and growth of the Y123 phase allow for thegreatest possible yield of the superconducting phase. In contrast to a previous report,our finding, through crystallographic studies of the as-synthesized material, isthat in spite of a beryllium excess being provided in the precursor, berylliumdoes not substitute into the Y123 crystal lattice, instead forming an associatephase which comes to dominate at high doping levels, to the detriment of theY123 phase. In addition, we are able unambiguously to refute the previouslyreported increase in superconducting transition temperature at low beryllium dopinglevels.

ReducedN-Alkyl Substituted Bis(imino)pyridine Cobalt Complexes: Molecular and Electronic Structures for Compounds Varying by Three Oxidation States

The stepwise 1-3 electron reduction of the N-alkyl substituted bis(imino)pyridine cobalt dichloride complexes, ((R)APDI)CoCl(2), was studied where (R)APDI = 2,6-(RN=CMe)(2)C(5)H(3)N, R = C(6)H(11) (Cy), CHMe(2) ((i)Pr). One electron reduction with either zinc metal or NaBEt(3)H furnished the bis(imino)pyridine cobalt monochloride compounds, ((R)APDI)CoCl. X-ray diffraction on the ((iPr)APDI)CoCl derivative established a distortion from square planar geometry where the chloride ligand is lifted out of the idealized cobalt-chelate plane. Superconducting Quantum Interference Device (SQUID) magnetometry on both compounds established spin crossover behavior with an S = 1 state being predominant at room temperature. Computational studies, in combination with experimental results, establish that the triplet spin isomer arises from a high spin Co(II) center (S(Co) = 3/2) antiferromagnetically coupled to a bis(imino)pyridine chelate radical anion, [PDI](-) (S(PDI) = 1/2). At lower temperatures, the Co(II) ion undergoes a spin transition to the low spin form (S(Co) = 1/2) and antiferromagnetic coupling gives rise to the observed diamagnetic ground state. Replacing the chloride ligand with a methyl group, namely ((R)APDI)CoCH(3), also yielded distorted compounds, albeit less pronounced, that are diamagnetic at room temperature. Two electron reduction of the ((R)APDI)CoCl(2) derivatives with excess 0.5% sodium amalgam or 2 equiv of NaBEt(3)H furnished the bis(chelate)cobalt complexes, ((R)APDI)(2)Co, while three electron reduction with 3 equiv of sodium naphthalenide yielded the cobalt dinitrogen anions, [Na(solv)(3)][((R)APDI)CoN(2)] (solv = THF, Et(2)O). Both bis(chelate) compounds were crystallographically characterized and determined to have S = 3/2 ground states by SQUID magnetometry and electron paramagnetic resonance (EPR) spectroscopy. Computational studies, in combination with metrical parameters determined from X-ray diffraction, establish a high spin (S(Co) = 3/2) cobalt(II) center with two bis(imino)pyridine chelate radical anions. Antiferromagnetic coupling between the two chelate centered radicals is mediated by a doubly occupied t(2g) cobalt orbital and gives rise to the observed overall quartet ground state.

Development of vortex state in circular magnetic nanodots: Theory and experiment

We compare magnetic reversal of nanostructured circular magnetic dots of different sizes. This comparison is based on superconducting quantum interference device (SQUID) magnetometry, neutron scattering, Monte Carlo simulation, and analytical calculations and is quantified using a parameter which characterizes the variation in the hysteresis curve width. Below a critical dot diameter, the magnetic reversal occurs by coherent rotation and above that diameter, the reversal occurs by formation of a magnetic vortex. The vortex-core diameter is controlled by competing magnetic energy contributions. For 20-nm-thick Fe dots, the values of the critical diameter (58--60 nm) and the vortex core (16--19 nm) are in very good agreement between the different experimental and theoretical methods: neutron scattering, SQUID magnetometry, Monte Carlo simulations, and analytical calculations.

Effects related to deposition temperature of ZnCoO films grown by atomic layer deposition - uniformity of Co distribution, structural, optical, electrical and magnetic properties

In the present study we report on properties of ZnCoO films grown at relatively low temperature by the Atomic Layer Deposition, using two reactive organic zinc precursors (dimethylzinc and diethylzinc). The use of these precursors allowed us the significant reduction of a growth temperature to below 300oC. The influence of growth conditions on the Co distribution in ZnCoO films, their structure and magnetic properties was investigated using Secondary Ion Mass Spectroscopy, Scanning Electron Microscopy, Cathodoluminescence, Energy Dispersive X-ray Spectrometry (EDX), X-ray diffraction and Superconducting Quantum Interference Device magnetometry. We achieved high uniformity of the films grown at 160{\deg}C. Such films are paramagnetic. Films grown at 200{\deg} and at higher temperature are nonuniform. Formation of foreign phases in such films was detected using high resolution EDX method. These samples are not purely paramagnetic and show weak ferromagnetic response at low temperature.

Magnetic characterization by SQUID and FMR of a biocompatible ferrofluid based onFe3O4

Biocompatible superparamagnetic iron oxide nanoparticles of magnetite coated withdextran were magnetically characterized using the techniques of SQUID (superconductingquantum interference device) magnetometry and ferromagnetic resonance (FMR).The SQUID magnetometry characterization was performed by isothermal measurementsunder applied magnetic field using the methods of zero-field-cooling (ZFC) andfield-cooling (FC). The magnetic behavior of the nanoparticles indicated theirsuperparamagnetic nature and it was assumed that they consisted exclusively ofmonodomains. The transition to a blocked state was observed at the temperatureTB = (43 ± 1) K for frozenferrofluid and at (52 ± 1) K for the lyophilized ferrofluid samples. The FMR analysis showed that the derivative peak-to-peak linewidth(ΔHPP), gyromagneticfactor (g), number ofspins (NS), and spin–spinrelaxation time (T2) were strongly dependent on both temperature and super-exchange interaction. Thisinformation is important for possible nanotechnological applications, mainly those whichare strongly dependent on the magnetic parameters.

Compensation-dependent in-plane magnetization reversal processes inGa1−xMnxP1−ySy

We report the effect of dilute alloying of the anion sublattice with S on the in-plane uniaxial magnetic anisotropy and magnetization reversal process in ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{P}$ as measured by both ferromagnetic resonance (FMR) spectroscopy and superconducting quantum interference device (SQUID) magnetometry. At $T=5\text{ }\text{K}$, raising the S concentration increases the uniaxial magnetic anisotropy between in-plane $⟨011⟩$ directions while decreasing the magnitude of the (negative) cubic anisotropy field. Simulation of the SQUID magnetometry indicates that the energy required for the nucleation and growth of domain walls decreases with increasing $y$. These combined effects have a marked influence on the shape of the field-dependent magnetization curves; while the $[0\overline{1}1]$ direction remains the easy axis in the plane of the film, the field dependence of the magnetization develops double hysteresis loops in the [011] direction as the S concentration increases, similar to those observed for perpendicular magnetization reversal in lightly doped ${\text{Ga}}_{1\ensuremath{-}x}{\text{Mn}}_{x}\text{As}$. The incidence of double hysteresis loops is explained with a simple model whereby magnetization reversal occurs by a combination of coherent spin rotation and noncoherent spin switching, which is consistent with both FMR and magnetometry experiments. The evolution of magnetic properties with S concentration is attributed to compensation of Mn acceptors by S donors, which results in a lowering of the concentration of holes that mediate ferromagnetism.

Synthesis of novel magnetic iron metal–silica (Fe–SBA-15) and magnetite–silica(Fe3O4–SBA-15) nanocomposites with a high iron content using temperature-programedreduction

Magnetic iron metal–silica and magnetite–silica nanocomposites have been preparedvia temperature-programed reduction (TPR) of an iron oxide–SBA-15 (SBA:Santa Barbara Amorphous) composite. TPR of the starting SBA-15 supportedFe2O3 generated Fe3O4 and FeO as stepwise intermediates in the ultimate formation of Fe–SBA-15. Thecomposite materials have been characterized by means of x-ray diffraction, highresolution transmission electron microscopy and SQUID (superconducting quantuminterference device) magnetometry. The Fe oxide and metal components forma core, as nanoscale particles, that is entrapped in the SBA-15 pore network.Fe3O4–SBA-15 and Fe–SBA-15 exhibited superparamagnetic properties with a total magnetization value of17 emu g−1. The magnetite–silicacomposite (at an Fe3O4 loading of 30% w/w) delivered a magnetization that exceeded values reported in the literatureor obtained with commercial samples. Due to the high pore volume ofthe mesoporous template, the magnetite content can be increased to83% w/w with a further enhancement of magnetization.

Impact of electron-electron spin interaction on electron spin relaxation of nitroxide diradicals and tetraradical in glassy solvents between 10 and 300 k.

To determine the impact of electron-electron spin-spin interactions on electron spin relaxation rates, 1/T1 and 1/Tm were measured for nitroxide monoradical, diradical, and tetraradical derivatives of 1,3-alternate calix[4]arenes, for two pegylated high-spin nitroxide diradicals, and for an azine-linked nitroxide diradical. The synthesis and characterization by SQUID (superconducting quantum interference device) magnetometry of one of the high-spin diradicals, in which nitroxides are conformationally constrained to be coplanar with the m-phenylene unit, is reported. The interspin distances ranged from about 5-9 A, and the magnitude of the exchange interaction ranged from >150 to >0.1 K. 1/T1 and 1/Tm were measured by long-pulse saturation recovery, three-pulse inversion recovery, and two-pulse echo decay at X-band (9.5 GHz) and Q-band (35 GHz). For a diradical with interspin distance about 9 A, relaxation rates were only slightly faster than for a monoradical with analogous structure. For interspin distances of about 5-6 A, relaxation rates in glassy solvents up to 300 K increased in the order monoradical < diradical < tetraradical. Modulation of electron-electron interaction enhanced relaxation via the direct, Raman, and local mode processes. The largest differences in 1/T1 were observed below 10 K, where the direct process dominates. For the three diradicals with comparable magnitude of dipolar interaction, 1/Tm and 1/T1 were faster for the molecules with more flexible structures. Relaxation rates were faster in the less rigid low-polarity sucrose octaacetate glass than in the more rigid 4:1 toluene/chloroform or in hydrogen-bonded glycerol glasses, which highlights the impact of motion on relaxation.

Loss of long-range magnetic order in a nanoparticle assembly due to random anisotropy

We have used soft x-ray photoemission electron microscopy (XPEEM) combined with x-raymagnetic circular dichroism (XMCD) and DC SQUID (superconducting quantuminterference device) magnetometry to probe the magnetic ground state in Fe thin filmsproduced by depositing size-selected gas-phase Fe nanoparticles with a diameter of 1.7 nm(∼200 atoms) onto Si substrates. The depositions were carried out in ultrahigh vacuum conditions andthicknesses of the deposited film in the range 5–50 nm were studied. The magnetometry data areconsistent with the film forming a correlated super-spin glass with a magnetic correlation length∼5 nm. The XPEEM magnetic maps from the cluster-assembled films were compared to thosefor a conventional thin Fe film with a thickness of 20 nm produced by a molecular beamepitaxy (MBE) source. Whereas a normal magnetic domain structure is observedin the conventional MBE thin film, no domain structure could be observed inany of the nanoparticle films down to the resolution limit of the XMCD basedXPEEM (100 nm) confirming the ground state indicated by the magnetometrymeasurements. This observation is consistent with the theoretical prediction that anarbitrarily weak random anisotropy field will destroy long-range magnetic order.

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

We report on the metalorganic chemical vapor deposition of $\mathrm{GaN}:\mathrm{Fe}$ and $(\mathrm{Ga},\mathrm{Fe})\mathrm{N}$ layers on $c$-sapphire substrates and their thorough characterization via high-resolution x-ray diffraction, transmission electron microscopy (TEM), spatially resolved energy dispersive x-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably ${\mathrm{Fe}}_{x}\mathrm{N}$ with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. According to Hall effect measurements, electrons from residual donors are trapped by midgap Fe acceptor states in the limit of low iron content $x\ensuremath{\lesssim}0.4%$, indicating that the concentration of ${\mathrm{Fe}}^{2+}$ ions increases at the expense of Fe ions in the $3+$ charge state. This effect is witnessed by PL measurements as changes in the intensity of the ${\mathrm{Fe}}^{3+}$-related intraionic transition, which can be controlled by codoping with Si donors and Mg acceptors. In this regime, EPR of ${\mathrm{Fe}}^{3+}$ ions and Curie-like magnetic susceptibility are observed. As a result of the spin-orbit interaction, ${\mathrm{Fe}}^{2+}$ does not produce any EPR response. However, the presence of Fe ions in the $2+$ charge state may account for a temperature-independent Van Vleck--type paramagnetic signal that we observe by SQUID magnetometry. Surprisingly, at higher Fe concentrations, the electron density is found to increase substantially with the Fe content. The coexistence of electrons in the conduction band and Fe in the $3+$ charge state is linked to the gradient in the Fe concentration. In layers with iron content $x\ensuremath{\gtrsim}0.4%$ the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. A set of precautions has been undertaken in order to rule out possible sources of spurious ferromagnetic contributions. Under these conditions, a ferromagneticlike response is shown to arise from the $(\mathrm{Ga},\mathrm{Fe})\mathrm{N}$ epilayers, it increases with the iron concentration, it persists up to room temperature, and it is anisotropic---i.e., the saturation value of the magnetization is higher for in-plane magnetic field. We link the presence of ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced by TEM and EDS studies. This interpretation is supported by magnetization measurements after cooling in and without an external magnetic field, pointing to superparamagnetic properties of the system. It is argued that the high temperature ferromagnetic response due to spinodal decomposition into regions with small and large concentration of the magnetic component is a generic property of diluted magnetic semiconductors and diluted magnetic oxides showing high apparent Curie temperature.

Optimized electrochemical performance of LiFePO 4 at 60 °C with purity controlled by SQUID magnetometry

The local structure and magnetic properties of a series of carbon-coated LiFePO 4 particles prepared under different conditions are analyzed with X-ray diffractometry (XRD), FTIR and Superconducting Quantum Interference Device (SQUID) magnetometry for comparison. While nano-sized ferromagnetic particles (γ-Fe 2O 3 clusters) are detected by magnetic measurements in samples grown from iron(II) oxalate, such ferromagnetic clusters do not exist in the optimized samples grown from FePO 4(H 2O) 2. FTIR analyses show that carbon does not penetrate significantly inside the LiFePO 4 particles despite the fact that it has been very efficient in reduction of Fe 3+ to prevent γ-Fe 2O 3 clustering, thus pointing to a gas-phase reduction process. The impact of the carbon coating on the electrochemical properties is also reported. No iron dissolution was observed after 200 charge–discharge cycles at 60 °C for cells containing lithium foil, lithium titanate or graphite negative electrodes.

Preparation of magnetic nanoparticles by pulsed plasma chemical vapor synthesis

FePt nanoparticle is expected as a candidate for the magnetic material of the high density recording media. We attempted to synthesize FePt alloy nanoparticles using 13.56 MHz glow discharge plasma with the pulse operation of a square-wave on/off cycle of plasma discharge to control the size of nanoparticles. Vapors of metal organics, Biscyclopentadienyl iron (ferrocene) for Fe and (Methylcyclopentadienyl) trimethyl platinum for Pt, were introduced into the capacitively coupled flow-through plasma chamber, which consisted of shower head RF electrode and grounded mesh electrode. Synthesis experiments were conducted at room temperature under the conditions of pressure 0.27 Pa, source gas concentration 0.005 Pa, gas residence time 0.5 s and plasma powers 60 watts. Pulse width for plasma duration was chosen from 0.5 to 30 s and plasma off period was 4 s to each pulse operation. Visual observations during the particle growth showed plasma emission in the bulk region was increased with the particle growth. These were theoretically explained by using the model for both transient particle charging in the plasma and single particle behavior in the stationary plasma as well as assuming the similarity between the negative charged particle and negative gas containing plasma. Synthesized nanoparticles were directly collected onto TEM grid, which was placed just below the grounded mesh electrode in the plasma reactor downstream. TEM pictures showed two kinds of particles in size, one of which was nanometer size and isolated with crystal structures and the other appeared agglomerate of nanometer size particles. The size of agglomerated particle was controlled in the 10–120 nm range by varying the plasma-on time from 0.5 to 30 s, although the nanometer size particles did not change. The composition of FePt alloy particles could be altered by adjusting the source gas feed ratio. Also magnetization of FePt nanoparticles was measured by use of SQUID (superconducting quantum interference device) magnetometry measurements. As-synthesized FePt nanoparticles did not exhibit loop-shape characteristic, which indicated superpamagnetic property. Annealed nanoparticles with the composition of Fe58Pt42 at 650°C in atmospheric hydrogen showed clear hysterisis loop with the coercivity as large as 10 KOe.

Hydrothermal synthesis and characterization of a layered cobalt phenylphosphonate, Co(PhPO3)(H2O)

We report the hydrothermal synthesis and characterization of a layered cobalt phenylphosphonate. Unlike most metal phosphonates reported to date, the structure was solved by single crystal X-ray diffraction (SC-XRD). Co(ii) centres are hexa-coordinated by oxygen and the octahedra corner-share into a layer. The layers are capped by phenylphosphonate groups, where the phenyl groups define a hydrophobic bilayer region. The material was also characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and SQUID (superconducting quantum interference device) magnetometry. The material undergoes an antiferromagnetic transition at a relatively low Néel temperature of 4.0 K, while the Curie-Weiss temperature of -76.5 K reflects the low-dimensionality of the magnetic structure. The effective magnetic moment of 5.01 micro(B) per Co(2+) verifies a high-spin configuration and an octahedral coordination of the metal centres. This layered material was correctly predicted in the literature from powder data, adds to the structural diversity of the cobalt phosphonates, and may be useful as an intercalation or exfoliation compound.

Weakening of charge order and antiferromagnetic to ferromagnetic switch over in Pr0.5Ca0.5MnO3 nanowires

We have prepared crystalline nanowires (diameter ∼50nm, length ∼a few microns) of the charge-ordering manganite Pr0.5Ca0.5MnO3 using a low reaction temperature hydrothermal method and characterized them using x-ray diffraction, transmission electron microscopy, superconducting quantum interference device (SQUID) magnetometry and electron magnetic resonance measurements. While the bulk sample shows a charge ordering transition at 245 K and an antiferromagnetic transition at 175 K, SQUID magnetometry and electron magnetic resonance experiments reveal that in the nanowires phase, a ferromagnetic transition occurs at ∼105K. Further, the antiferromagnetic transition disappears and the charge ordering transition is suppressed. This result is particularly significant since the charge order in Pr0.5Ca0.5MnO3 is known to be very robust, magnetic fields as high as 27 T being needed to melt it.

Magnetic property based characterization of rust on weathering steels

The characterization of rusts on weathering steels is important in understanding the origin of their corrosion resistance. Rust consists of several phases, e.g. α-, β- and γ-FeOOH, which are anti-ferromagnetic with different Neél temperatures. Rust on so-called advanced weathering steel containing 3 wt.% Ni [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127–136] contains in addition a ferrimagnetic spinel phase [M. Kimura, H. Kihira, Y. Ishii, T. Mizoguchi, in: Proc. 13th Asian-Pacific Corrosion Control Conference, Osaka, 2003; M. Kimura, H. Kihira, N. Ohta, M. Hashimoto, T. Senuma, Corros. Sci., this volume; M. Kimura, N. Ohta, H. Kihira, Mater. Trans. JIM, in press]. The nanostructure of real rust cannot be elucidated satisfactorily only with conventional analytical methods such as X-ray diffraction, because of the complex mixture of phases with fine and imperfect crystallites. Because of the short range of the super-exchange coupling between Fe ions in a solid, the magnetic properties can give information on local configurations even in the absence of perfect crystalline coherence. Therefore, the magnetic properties of rust samples were investigated in detail using a Superconducting Quantum Interference Device (SQUID) magnetometer and Mössbauer spectroscopy. SQUID magnetometry is effective to determine the quantity of the ferrimagnetic phase. The temperature dependence of the Mössbauer spectrum gives information about not only the fractions of the phases but also the distribution of grain volume, V, in each phase according to the super-paramagnetic relaxation effect. This approach has been applied to rust of conventional [T. Okada, Y. Ishii, T. Mizoguchi, I. Tamura, Y. Kobayashi, Y. Takagi, S. Suzuki, H. Kihira, M. Ito, A. Usami, K. Tanabe, K. Masuda, Jpn. J. Appl. Phys. 39 (2003) 3382] and advanced weathering [H. Kihira, A. Usami, K. Tanabe, M. Ito, G. Shigesato, Y. Tomita, T. Kusunoki, T. Tsuzuki, S. Ito, T. Murata, in: Proc. Symp. on Corrosion and Corrosion Control in Saltwater Environments, Honolulu, 1999, The Electrochemical Soc., pp. 127–136] steels. The grains of the rust formed on advanced weathering steel have clearly bimodal Gaussian distributions of volume with peaks at V ≈ 5 × 10 −24 m 3 and V ≈ 16 × 10 −24 m 3 in α-FeOOH and β-FeOOH phases. The outer layer has grains of γ-FeOOH which are an order of magnitude smaller. The inner layer, in contrast, has a continuous distribution of grain volume, consistent with the formation of a continuous densely packed thin protective rust layer which prevents further corrosion.