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A large rotating magnetocaloric effect (RMCE) was always observed in the materials with anisotropic magnetisms, for example, ferromagnetism vs antiferromagnetism or paramagnetism, at different crystallographic directions. In this work, anisotropic ferromagnetic susceptibility is utilized to implement low-field (≤2 T) large RMCE in the textured polycrystalline HoB2 alloy. The x-ray diffraction and scanning electron microstructure results reveal that the arc-melted HoB2 exhibits preferred grain orientation along the solidification direction. The measured rotating magnetic entropy changes (−ΔSR) and refrigeration capacity are 6.27 J/kg K and 73.7 J/kg, respectively, under the magnetic field change of 1 T. They are comparable with those of other materials contributed by anisotropic magnetisms. Our results suggest that the polycrystal HoB2 alloy is a promising material for practical application of magnetic refrigeration based on RMCE. [ABSTRACT FROM AUTHOR]

The magnetically actuated robot has valuable potential in biomedicine, bioengineering, and biophysics for its capability to precisely manipulate particles or biological tissues. However, the deformability of rigid robots with predetermined shapes is limited, which constricts their functions and causes inconvenience for robots' movement in constricted space. In this study, we proposed a feasible and efficient ferrofluid-based robot for the transportation of tiny particles and blocks. In addition, a method to generate a patterned magnetic field is also introduced to model a ferrofluid-based robot with an adaptive shape. Benefiting from the paramagnetism and fluidity of the ferrofluid-based robot, it also demonstrates outstanding motion accuracy and output force on a superhydrophobic surface. Because of its excellent motion characteristics, high motion accuracy, and high measured output force, the proposed ferrofluid-based robot has great advantages in the field of microoperation. The correlation coefficient between the motion trajectory of the ferrofluid-based robot and the motion trajectory of the micro-stages is 0.9967. The position error is less than 1.5% of the total stroke. [ABSTRACT FROM AUTHOR]

We demonstrate the detection of the Brownian relaxation frequency of 250 nm diameter magnetic beads using a lab-on-chip platform based on current lines for exciting the beads with alternating magnetic fields and highly sensitive magnetic tunnel junction (MTJ) sensors with a superparamagnetic free layer. The first harmonic out-of-phase component of the MTJ response gives the imaginary part of the magnetic bead susceptibility, which peaks at the Brownian relaxation frequency. This work paves the way to on-chip implementation of Brownian magnetorelaxometry in innovative 'lab-on-a-bead' assays for biomolecular recognition. [ABSTRACT FROM AUTHOR]

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line 57Fe Mössbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive 57Mn ions at room temperature. The Mössbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence rules out an ordered magnetic state (which had been previously proposed) but are well accounted for on the basis of Fe3+ paramagnetic centers on substitutional Zn sites with unusually long relaxation times (>20 ns). [ABSTRACT FROM AUTHOR]

Comparison between densities of paramagnetic Ge dangling bond defects and shallow acceptor traps at interfaces of the condensation-grown Si1-xGex layers (0.28≤x≤0.93) with thermal SiO2 as a function of Ge fraction, x, reveals quantitative agreement. Moreover, defect densities detected in both magnetic resonance and electrical experiments exhibit reversible passivation-depassivation behavior with respect to hydrogen indicating observation of the same defect (Ge Pb1 center). The corresponding energy level is estimated to lie at 0.35±0.10 eV above the valence band in bulk Si, which makes these defects behave as shallow acceptors in Ge-rich Si1-xGex. [ABSTRACT FROM AUTHOR]

We report on the magnetic actuation of superparamagnetic particles in a microfluidic channel. The formation of a highly confined and dynamic plug of particles extending over the cross section of the microchannel is enabled by superposing a static and a time-varying magnetic field. The latter is generated by an electromagnet and focused across the microchannel using microstructured soft magnetic tips. Finite element calculations of the magnetic force distribution do compare well with experiments. Our system allows maximizing the exposure of superparamagnetic particles to a microfluidic flow of interest for integrated lab-on-a-chip applications. [ABSTRACT FROM AUTHOR]

Magnetodielectric coupling effects of single phase multiferroic Pb(Fe0.5Nb0.5)O3 ceramics have been studied using standard ferroelectric measurements and electron paramagnetic resonance (EPR). Changes in the electrical polarization behavior were observed in the paramagnetic to weakly magnetized antiferromagnetic transition near 103 K associated with a rhombohedral to monoclinic symmetry reduction. The analysis of changes in the EPR spectral parameters confirms the transition from paramagnetic to weakly magnetized antiferromagnetic and reveals noticeable anomalies in the high temperature region near the ferroelectric-paraelectric transition (383 K), which are correlated with the tetragonal-to-cubic symmetry change and the characteristic diffuse phase transition of this material. [ABSTRACT FROM AUTHOR]

We proposed an explanation of the recent observations by Zaretsky [Appl. Phys. Lett. 92, 011913 (2008)] who discovered sharp increase in nickel plasticity under impact loading near Curie temperature TC. Growth of plasticity is explained by reduction in dynamical deceleration of dislocations controlled by their interaction with paramagnetic obstacles. The decreased contribution of these obstacles is due to spin-dependent transitions in internal magnetic field of ferromagnetic in radical pair dislocation-obstacle from strong to weak bonding states. The main contribution to the effect is from fields of magnetic fluctuations which have a large growth near Curie point. [ABSTRACT FROM AUTHOR]

The effect of applied magnetic field (H) on the magnetic properties of Sm0.52Sr0.48MnO3 single crystal in the paramagnetic (PM) state has been investigated. We observe a field induced steplike jump in magnetization (M) above TC (110 K). The temperature and magnetic field dependence of susceptibility reveal that the PM phase of this system is quite complicated due to the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions. The nature of magnetic interaction changes abruptly from AFM to FM at around 3.5 T, above which M ceases the steplike jump. [ABSTRACT FROM AUTHOR]

For ellipsoidal magnetic nanoparticles the values of surface-induced uniaxial anisotropy have been derived from an analytical model as functions of aspect ratios and particle sizes. The authors show that this specific anisotropy can stabilize multiple magnetic states in the system, suppress demagnetization effects, and prevent superparamagnetism. The calculated phase diagrams indicate the stability regions of different phases and the transition fields between them. By tuning sizes, geometry, and surface anisotropy of elongated particles a well-defined sequence of magnetic switching transitions can be realized in prescribed magnetic fields. This can be used in magnetic recording and spin electronic technologies. [ABSTRACT FROM AUTHOR]

We present a method to move and control drops of water on superhydrophobic surfaces using magnetic fields. Small water drops (volume of 5–35 μl) that contain fractions of paramagnetic particles as low as 0.1% in weight can be moved at relatively high speed (7 cm/s) by displacing a permanent magnet placed below the surface. Coalescence of two drops has been demonstrated by moving a drop that contains paramagnetic particles towards an aqueous drop that was previously pinned to a surface defect. This approach to microfluidics has the advantages of faster and more flexible control over drop movement. [ABSTRACT FROM AUTHOR]

For phase-separated La0.275Pr0.35Ca0.375MnO3 manganite, a steplike charge-ordered antiferromagnetic-ferromagnetic transition was observed by field induction and accompanied by a sudden drop of resistivity. The results can be explained in terms of the spin reorientation in the antiferromagnetic (AFM) phase and simultaneous destruction of orbital ordering by a magnetic field. Combined with specific heat and magnetization measurements, the electronic state density at Fermi energy was greatly enhanced at 5 T, which shows the increase of carrier number due to delocalization effect, by analogy with the spin reorientation due to destruction of orbital ordering by magnetic field. The present results prove that the strong coupling among spin, charge, and orbital ordering would be the main cause of existing complex physical behavior at low temperature, which depends sensitively on the spin orientation of adjacent charge-ordered AFM domains and can be controlled by applied field. [ABSTRACT FROM AUTHOR]

We report millimeter-wave magneto-optical measurements on the high-spin molecule, Cr10(OMe)20(O2CCMe3)10. The dependence of the electron paramagnetic resonance as a function of orientation and temperature demonstrates that this compound behaves as a single molecule magnet, and exhibits one of the smallest zero-field splittings (D=-0.045±0.004 K) yet reported for such a system. [ABSTRACT FROM AUTHOR]

A three-dimensional (3D) electron spin resonance (ESR) microimaging system, operating in pulse mode at 9 GHz is presented. This microscope enables the acquisition of spatially resolved magnetic resonance signals of free-radicals in solid or liquid samples with a resolution of up to ∼3.5×7×11.4 μm in 20 min of acquisition. The detection sensitivity at room temperature is ∼1.2×109 spins/[Square_Root]Hz, which enables the measurement of ∼2×107 spins in each voxel after 60 min of acquisition. The resolution and detection sensitivity are the best obtained so far for ESR at ambient conditions of temperature and pressure. This ESR microscope can be employed in the investigation of a variety of samples in the fields of botany, life sciences, and materials science. [ABSTRACT FROM AUTHOR]

We describe a technique to optically characterize superparamagnetism. Faraday rotation measurements are performed on a superparamagnetic nanocomposite using small alternating current magnetic fields. The superparamagnetism of the iron oxide nanoparticles causes signals at the uneven harmonics of the magnetic field frequency. These signals provide information on the magnetic moment of the superparamagnetic nanoparticles. Dia- and paramagnetism do not cause signals at higher harmonics, resulting in a high sensitivity to superparamagnetism, even in samples with large dia- or paramagnetic contributions. This technique provides a rapid, economical method to characterize superparamagnetism in composite samples not easily accessible by other techniques. [ABSTRACT FROM AUTHOR]

A sharp microwave response centered at zero magnetic field was observed in manganese- and iron-doped Na[sub 2]O-CaO-MgO-SiO[sub 2] glasses with phase opposite to the normal Mn[sup +2] and Fe[sup +3] paramagnetic signals. The response can be described as magneto-induced microwave conductivity in the dielectric glass that derives from spin-dependent charge migration within the first coordination sphere of the paramagnetic ion. In contrast to the spin-polarized tunneling in ferromagnets between different valence states of metals, the observed effect is due to spin-dependent tunneling that occurs in the vicinity of manganese or iron in diluted paramagnetic systems. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In order to study the effect of applied magnetic field on the superparamagnetic relaxation behavior of small Co particles, magnetization measurements were carried out on as-prepared and annealed granular samples of Co[sub 20]Ag[sub 80] and Co[sub 25]Ag[sub 75]. Values of the superparamagnetic blocking temperature T[sub B][sup -] were obtained from the characteristic peak in the zero-field-cooled magnetization. Consistent with existing models, it was found that the initial decrease of T[sub B][sup -] with applied magnetic field is quadratic. An estimate of the magnetic anisotropy “energy density” K[sub u] yielded a value which is two orders of magnitude greater than the value for bulk cobalt. The results reported here underscore the importance of considering the effect of superparamagnetic relaxation on the performance of nanostructured magnetic materials. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]