High-resolution Magnetization Research Articles

Superconducting magnetization and pressure effect on Tc in the infinite-layer high- Tc superconductors

High-resolution neutron powder diffraction experiments and magnetization measurements were performed for a series of the electron-doped infinite-layer high-temperature superconductors Sr 1− x R x CuO 2 (R=La, Pr; 0.07⩽ x⩽0.15). Zero-field-cooled magnetization measurements performed for the powder Sr 0.9Pr 0.1CuO 2 sample under hydrostatic pressure up to 0.5 GPa at a magnetic field of 0.005 T revealed a downward shift of the onset temperature T c onset of the diamagnetic response described by the pressure derivative d T c onset/d p=−(0.75±0.30) K/GPa. By measuring the reversible superconducting magnetization for the powder aligned Sr 0.9Pr 0.1CuO 2 sample at high fields 1⩽ μ 0 H⩽5 T, we found that the 3D-lowest-Landau-level approximation is a good description of fluctuation magnetization, if one takes into the curvature of the critical line B c2( T)∝| T− T c| 4/3.

Precursor diamagnetism above the superconducting transition in YNi $_\mathsf{2}$ B $_\mathsf{2}$ C

High-resolution SQUID magnetization measurements in a single crystal of YNi2B2C around the superconducting transition are reported. The diamagnetic magnetization −Mfl at constant field H as a function of temperature and isothermal magnetization curves −Mfl vs. H are used to derive insights on precursor phenomena approaching the bulk transition temperature Tc(H =0 ) =1 5.25 ± 0.02 K. The precursor diamagnetism is found strongly enhanced with respect to the conventional Ginzburg-Landau value for Gaussian fluctuations and the curves −Mfl vs. H exhibit an upturn with the field and hysteretic effects up to T ∗ =1 5.4 K. These results are interpreted in terms of a non-zero order parameter in super- conducting droplets above the bulk Tc. These droplets are likely to be related to inhomogeneities resulting from small amount of boron to carbon substitutions.

Precursor diamagnetism above the superconducting transition inLa1.9Sr0.1CuO4

High-resolution isothermal magnetization curves above the transition temperature ${T}_{c}$ in a single crystal of superconducting underdoped cuprate ${\mathrm{La}}_{1.9}{\mathrm{Sr}}_{0.1}{\mathrm{CuO}}_{4}$ ${(T}_{c}=26\mathrm{K})$ are reported. For magnetic field $Hg~1\mathrm{kOe}$ the diamagnetic magnetization is rather well described by the Ginzburg-Landau theory in finite fields, as observed in previous works. On the contrary, in the low-field range and for T within ${T}_{c}+2\mathrm{K},$ evidence is given for precursor diamagnetism of different character, with magnetization curves displaying an upturn in the field dependence and magnetic-history dependent effects below $T\ensuremath{\simeq}27\mathrm{K}.$ These findings are the magnetic counterpart of the observation by scanning superconducting quantum interference device microscopy of regions precursor of bulk superconductivity. The interpretation of the experimental data in terms of phase fluctuations of local order parameter is shown to account for most of the aspects of the precursor diamagnetism, which appears to be a general phenomenon in cuprates.

Magnetic Phase Diagram of the Heavy Fermion Superconductor PrOs4Sb12

We investigated the magnetic phase diagram of the first Pr-based heavy fermion superconductor PrOs 4 Sb 12 by means of high-resolution dc magnetization measurements in low temperatures down to 0.06 K. The temperature dependence of the magnetization M ( T ) at 0.1 kOe exhibits two distinct anomalies at T c1 =1.83 K and T c2 =1.65 K, in agreement with the specific heat measurements at zero field. Increasing magnetic field H , both T c1 ( H ) and T c2 ( H ) move toward lower temperatures without showing a tendency of intersecting to each other. Above 10 kOe, the transition at T c2 ( H ) appears to merge into a line of the peak effect which is observed near the upper critical field H c2 in the isothermal M ( H ) curves, suggesting a common origin for these two phenomena. The presence of the field-induced ordered phase (called phase A here) is confirmed for three principal directions above 40 kOe, with the anisotropic A-phase transition temperature T A : T A [100] > T A [111] > T A [110] . The present results are discussed on the basis of crystalline-electrical-field level schemes with a non-magnetic ground state, with emphasis on a Γ 1 singlet as the possible ground state of Pr 3+ in PrOs 4 Sb 12 .

Operation of a 920-MHz high-resolution NMR magnet at TML

As a milestone in the 1-GHz NMR magnet project that is being carried out at the Tsukuba Magnet Laboratory (TML), a 920-MHz high-resolution NMR magnet was successfully manufactured. It is made of 15%Sn-bronze-processed (Nb, Ti)/sub 3/Sn, Ta-reinforced (Nb, Ti)/sub 3/Sn, and NbTi conductors. The room-temperature bore of the cryostat is 54 mm in diameter. All the coils are cooled with pressurized superfluid helium at 1.55 K. The magnet was moved to a new building of the TML in December 2001. A persistent operation at 920 MHz started in April 2002. The field homogeneity after correcting with superconducting shim coils was less than 0.1 ppm in a sample volume. Field decay decreased to below 1.3 Hz/h at the beginning of July. NMR measurements using this magnet started in July.

Kerr observations of asymmetric magnetization reversal processes in CoFe/IrMn bilayer systems

The magnetization reversal process in the ferromagnetic layer of an exchange-biased Co90Fe10(20 nm)/Ir23Mn77(10 nm) film structure, deposited by dc-magnetron sputtering, is imaged by high-resolution Kerr microscopy. Additionally, high-resolution magnetization loops are measured by deriving the magnetization signal from the average image intensity. The magnetization reversal occurs first by magnetization rotation under the development of ripple-like structures. The modulated structures then partially switch, generating complicated multidomain configurations, which finally annihilate by large angle domain wall movement. The amount of magnetization rotation at different field directions is quantified by measuring the transversal magnetization components during reversal. A strong asymmetry, both in domain behavior and magnetization loop, between the forward and recoil branch of the magnetization reversal is found. The magnitude of asymmetry strongly depends on small angle misalignments between the direction of exchange-bias and the external magnetic field. The observed domain behavior is explained by anisotropy dispersion in the ferro- and antiferromagnetic layer. The observed differences for both branches of the hysteresis loop are described in terms of domain nucleation mechanisms due to changes in the antiferromagnetic layer leading to an effectively wider anisotropy distribution.

Nanostructure and magnetic properties of Fe 0.56Cu 0.44 films

X-ray diffraction, high-resolution transmission electron microscopy, Mössbauer effect and magnetisation investigations have been performed on sputtered Fe 0.56Cu 0.44 thin films, in which the Fe concentration is near the percolation threshold. Segregation into FCC-Cu rich and BCC-Fe rich phases takes place in the as-deposited film. This state is described in terms of the interfacial transient concentration and ferromagnetism, which originate from the ferromagnetic BCC-Fe in the centre of the individual grains, the iron-rich crystalline Fe(Cu) alloy lying near the interface and the paramagnetic copper-rich FCC-Cu(Fe) matrix. Annealing effects cause not only the evolution of the grain size of the BCC-nanocrystalites, but also the enrichment of Fe in this phase, leading to an increase of the interfacial sharpness. In addition, the magnetic coercive field is found to be enhanced. The coercivity shows a value as large as 24.2 mT for the sample annealed at 400°C. A contribution of the positive surface magnetic anisotropy ( K S=+0.1 mJ/m 2) to the coercivity is deduced.

Tumor resection in a shared-resource magnetic resonance operating room: experience at the University of Cincinnati.

At the University of Cincinnati, we have developed a shared-resource magnetic resonance operating suite that facilitates performance of both neurosurgical and diagnostic procedures in a single unit. The shared-resource magnetic resonance operating suite utilizes a Hitachi AIRIS II, 0.3-T, vertical field, open MRI unit located in the MROR. This magnet can be used for both diagnostic and interventional procedures. The addition of a rotating-operating table permits neurosurgical procedures to be performed outside of the 5-G line using standard neurosurgical equipment and operating microscopes. We review our results with the shared-resource magnetic resonance operating room including the tabulated results from 30 transsphenoidal procedures and 63 glioma procedures. In addition, 2832 diagnostic procedures have been performed in the first 4 years of use. The shared-resource intraoperative MRI facility produces high-quality intraoperative imaging studies, equal to those of high-resolution magnets, and is valuable in enabling the surgeon to achieve the planned degree of resection of glioma and pituitary tumors. The ability to perform diagnostic procedures in a shared unit has been a cost-effective solution for our institution.

Determination of the crystal and magnetic structures of Rn+1Co3n+5B2n (n=1, 2, and 3; R=Pr, Nd, and Dy)

The crystal and magnetic structures of the Rn+1Co3n+5B2n compounds (R=Pr, Nd, and Dy; n=1, 2, and 3) have been studied by high-resolution powder neutron diffraction and magnetization measurements. The RCo4B (n=1) and R3Co11B4 (n=2) samples are found to be single-phase compounds whereas R3Co11B4 is seen as impurity in R2Co7B3 (n=3). The crystal structures show the existence of unexpected very short cobalt–boron interatomic distances in R2Co7B3. This feature indicates a break in the regular stacking of the Rn+1Co3n+5B2n compounds for n=3 and may explain the absence of stable phases with 3<n<∞. The magnetic structures of RCo4B, R3Co11B4 and R2Co7B3 confirm that a large variety of magnetic moments exists for the cobalt atoms. The magnetism of the cobalt atoms situated in the 2c position is not affected by the substitution of boron for cobalt. On the contrary, the cobalt atoms situated on the 3g, 6i1, and 6i2 positions are carrying significantly reduced magnetic moments in comparison with those on the 2c sites. The R magnetic moments are found to be less sensitive to the presence of boron in their local environment. This behavior tends to indicate that due to the strongly localized 4f electron in the R atoms, the magnetic moment carried by the rare-earth atoms is not significantly modified by the presence of B. Finally, the direction of easy magnetization is found to be unchanged upon the substitution of boron for cobalt and is imposed by the R sublattice for the RCo4B, R3Co11B4, and R2Co7B3 compounds.

Determination of nearshore geologic structure off western Cape Breton Island, Nova Scotia, using high-resolution marine magnetics

New high-resolution magnetic data have been acquired along the coast of western Cape Breton Island near Cheticamp, Nova Scotia, in a transition zone between exposed, elevated basement of the Cape Breton highlands and the adjacent Carboniferous sediment-filled Magdalen Basin. These data were collected to provide continuity between the mapped onshore geology and the geophysical-based interpretations of offshore structure. Separation of the geologic component of the data from the effects of diurnal and other variations in the Earth's magnetic field was made difficult by recording problems at the nearby base recording station. Careful correlation of the fragmented station signal with records from a nearby permanent magnetic observatory enabled a reasonable diurnal signal to be synthesized and applied successfully to the data. Additional processing and filtering helped to enhance small anomalies in the data. Several low-amplitude, fairly linear magnetic anomalies are visible in the reduced anomaly data, generally trending north to northwest away from the coastline. Small-amplitude lineations in the offshore at Cheticamp are associated with folded, tilted, or faulted strata imaged on coincident seismic reflection data and are interpreted as representing juxtaposed units of Carboniferous strata. Other small anomalies appear to represent shallow contacts between intrusive or metasedimentary rocks visible in outcrops near the coast. A stronger, coast-parallel anomaly that extends across the study area from a regional magnetic high in the north is coincident with an offset in basement rocks or deeper strata beneath Carboniferous basin fill. This anomaly may mark part of the faulted transition zone between the elevated highlands of northwestern Cape Breton Island and the Magdalen Basin depocentre.

Persistent-mode operation of a 920 MHz high-resolution NMR magnet

Development of a high-field NMR magnet has been underway at the Tsukuba Magnet Laboratory of the National Institute for Materials Science. The magnet succeeded in a persistent-mode operation at 21.17 T in December 1999. A 283-day long-term operation was carried out from October 2000 to August 2001. It included a persistent operation at 21.6 T (920 MHz) for 108 days. This was the highest field that the superconducting magnets have ever achieved in a persistent operation. Field decay was less than 2 Hz/h. Field homogeneity after correcting with superconducting shim coils were less than 0.1 ppm in a sample volume. These results confirmed that this magnet had been successfully developed as a high-resolution NMR magnet.

Thermomagnetic irreversibility in rare-earth neodymium

We report high-resolution magnetisation measurements of long-range antiferromagnetically ordered pure rare-earth element Nd. These measurements show interesting thermomagnetic irreversibility that extends beyond the antiferromagnetic transition temperature T N(≈20 K). The low-field magnetisation behaviour shows a sharp increase below 7.0 K in this antiferromagnetically ordered system. Possible origins of this interesting behaviour have been discussed.

Magnetization study of the heavy fermion superconductor CeCoIn 5

We report the high-resolution dc magnetization measurements in the heavy fermion superconductor CeCoIn 5 at very low temperatures down to 50 mK in fields up to 125 kOe. A clear magnetization jump is observed at the upper critical field H c2 for both H‖ a and c axes in the isothermal magnetization curve below 0.7 K, indicating the existence of a first-order phase transition at H c2. It is likely that the first-order phase transition is ascribed to a strong Pauli paramagnetic suppression in the even-parity pairing. In the normal state above H c2 we found non-Fermi liquid behavior in the temperature dependence of the magnetization down to 150 mK, suggesting the presence of antiferromagnetic fluctuations.

１ＧＨｚ級ＮＭＲマグネットの開発

NMR spectrometers are considered to be an indispensable tool for structural biology. They are applied to determine the stereoscopic structure of protein molecules and to identify the chemical-reacting part between proteins and candidate medicines. Because the sensitivity and resolution of NMR spectrometers are improved with external magnetic fields, development projects of high-field NMR spectrometers have been carried out worldwide. At the Tsukuba Magnet Laboratory of the National Institute for Materials Science, the development of a high-field NMR magnet has been under way since 1995. The final target is to generate an additional 2.4T with an innermost coil, resulting in a central field of 23.5T corresponding to a 1H NMR frequency of 1GHz in a 54mm diameter room-temperature bore. The magnet was confirmed to operate as a high-resolution NMR magnet at 920MHz, using a Nb3Sn innermost coil. In the case of an NMR magnet, the required conditions of field homogeneity and stability are very strict. In this paper, we introduce the design issues of an NMR magnet by using our developed NMR magnet as an example. The future vision for high-field superconducting NMR magnets generating a field of 23.5T or more is also described.

Evidence for logarithmic corrections to the mean-field critical behavior in the weak itinerant ferromagnetNi3Al

The results of an elaborate analysis of high-resolution magnetization and ac suceptibility data unambiguously establish the existence of multiplicative logarithmic corrections (MLC) to single power laws in the asymptotic critical region near the ferromagnetic--paramagnetic phase transition in well-characterized polycrystalline ${\mathrm{Ni}}_{3}\mathrm{Al}$ samples. A crossover from this asymptotic critical behavior to the Gaussian fixed point occurs gradually over a fairly wide temperature range outside the critical regime. Accurate determination of the universal amplitude ratio ${R}_{\ensuremath{\chi}}{=DB}^{\ensuremath{\delta}\ensuremath{-}1}\ensuremath{\Gamma},$ the asymptotic critical exponents $\ensuremath{\beta},$ $\ensuremath{\gamma},$ and $\ensuremath{\delta}$ and the MLC exponents ${x}^{\ensuremath{-}},$ ${x}^{+},$ and ${x}^{0}$ for spontaneous magnetization, initial susceptibility and the magnetization versus field isotherm at ${T=T}_{C}$ (the Curie temperature), respectively, and a detailed comparison between theory and experiment indicate that the weak itinerant ferromagnet ${\mathrm{Ni}}_{3}\mathrm{Al},$ so far as its asymptotic critical behavior is concerned, is an experimental realization of an isotropic $d=3,$ $n=3$ ferromagnet in which the interactions between magnetic moments decay with distance (r) as $J(r)\ensuremath{\sim}{1/r}^{(3/2)d}.$

Critical magnetic properties of disordered Cr-rich FeCr alloys

A detailed analysis of high-resolution magnetisation data reveal that the critical behaviour of chemically well-homogenised high-purity disordered Cr 70Fe 30 and Cr 75Fe 25 alloys near the paramagnetic (PM)–ferromagnetic (FM) phase transition is similar to that of a three-dimensional Heisenberg ferromagnet. An ion-beam sputtered Cr 70Fe 30 thin film of 9.4 nm thickness exhibits the same critical behaviour as that of the bulk Cr 70Fe 30.

High Resolution Airborne Micromagnetics Used to Describe Initial Prospect Leads in the Development of Oil and Gas Drilling Prospects in the Transition Zone of the Gulf Coast

ABSTRACT Light hydrocarbons escape from petroleum reservoirs and move in a vertical to near-vertical path to the surface. The accompanying geochemical processes create locally-anomalous rock properties in the overlying near-surface formations that are geophysically measurable. Depending on the chemical elements involved, the resulting alteration will either enrich or destroy the magnetic minerals present, changing their magnetic susceptibilities and creating, respectively, either positive or negative magnetic anomalies. Because local, near-surface magnetic anomalies can also be caused by depositional processes or the structuring of the sediments, systematic follow-up is required to evaluate each magnetic lead. The goal is to first determine whether or not the magnetic anomaly signifies an alteration zone and, if so, to see if active hydrocarbon seepage is measurable. We intend to demonstrate the ability of high resolution airborne magnetic survey to provide; (1) a more detailed picture of basement structure and topography; (2) more importantly, a perspective of the region's near-surface structural grain; and (3) specific targets that have the potential of being seep-related and truly worthy of the greater expense of seismic definition, leasing and drilling. Viable drilling prospects can be developed more quickly and cost-effectively by using this method. Examples presented illustrate the contribution that high resolution magnetics can make in the exploration of the Gulf Coast Transition Zone. End_of_Record - Last_Page 457-------

Low-lying magnetic excitations inNi3Aland their suppression by a magnetic field

Results of high-resolution magnetization (M) measurements performed on well-characterized polycrystalline ${\mathrm{Ni}}_{3}\mathrm{Al}$ sample over wide ranges of temperature and external magnetic field are presented and discussed in the light of existing theoretical models. Contrary to the earlier claims that either Stoner single-particle excitations or nonpropagating spin fluctuations solely determine the temperature dependence of spontaneous magnetization $M(T,0),$ at low temperatures, we find that propagating transverse spin-density fluctuations (spin waves) almost entirely account for the thermal demagnetization of both $M(T,0)$ and ``in-field'' magnetization $M(T,H),$ at temperatures $T\ensuremath{\lesssim}{0.28T}_{C}$ ${(T}_{C}=\mathrm{Curie}\mathrm{point}).$ The spin-wave stiffness possesses a field-independent value of $69.6(14) \mathrm{meV} {\mathrm{\AA{}}\mathrm{}}^{2}$ which conforms well with those determined earlier from small-angle and inelastic neutron-scattering experiments. In the temperature range ${0.32T}_{C}\ensuremath{\lesssim}T\ensuremath{\lesssim}{0.92T}_{C},$ enhanced nonpropagating spin-density fluctuations (SF) give a contribution to $M(T,0)$ and $M(T,H)$ that completely overshadows the one arising from spin waves. In accordance with the predictions of a modified spin-fluctuation theory, proposed by the authors recently, the thermally excited SF's get strongly suppressed by magnetic field H while the zero-point SF's are relatively insensitive to H.

Moveable Intraoperative Magnetic Resonance Imaging Systems in the OR

Recently, the Seaman Family Magnetic Resonance Research Center, Calgary, Alberta, Canada, unveiled leading technology with its moveable intraoperative magnetic resonance imaging (MRI) system. The new system, which is housed in the OR, allows surgeons to use well-established neurosurgical techniques and instrumentation with the convenience of moving the high-resolution magnet in and out of the surgical field at any time. This mobility provides surgical team members with updated images that are vital to ensuring quality and determining the effect of surgery on brain structure and function. Based on experiences with the first 48 patients, this article describes the intraoperative MRI method and provides pertinent guidelines for safe perioperative care using this innovative MRI system.

Development of 1 GHz superconducting NMR magnet at TML/NRIM

Development of a 1 GHz superconducting NMR magnet is in progress at the Tsukuba Magnet Laboratory of the National Research Institute for Metals. The magnet will consist of two parts. The outer magnet of LTS coils is designed to generate a field of 21.1 T (900 MHz) in persistent current mode. The inner coil is designed to generate an additional 2.4 T, resulting in a central field of 23.5 T (1 GHz) in a 54 mm diameter bore at room temperature. As a high-resolution NMR magnet, field stability as well as field homogeneity is very important, which is especially difficult to achieve in the inner coil when exposed to extremely high magnetic fields that superconducting magnets have not yet encountered. The engineering design is complete and fabrication of the superconductors has begun. This report presents the results of the engineering design and R&D studies on the candidate superconductors for the inner coil, such as BSCCO, and improved Nb/sub 3/Al and Nb/sub 3/Sn.