On the magnetization reversal of the oxide-based exchange spring magnet

The role of the soft phase (Ni0.8Zn0.2Fe2O4) on the magnetization reversal and coercivity mechanism of the Ni0.8Zn0.2Fe2O4/BaFe12O19 nanocomposite has been investigated. The presence of the interacting field and the disorder in the nanocomposite has been confirmed by the variation of Jr/Jr(∞) vs Jd/Jr(∞) and the irreversible magnetization. To understand the relative strength of the pinning and the nucleation, the magnetic viscosity measurement has been done and the thermal activation volume has been estimated. From the Barbier plot and the activation volume measurement, the dominant mechanism governing the magnetization reversal process has been proposed.

Crystal-field interaction in the pyrochlore magnet Ho2Ti2O7

Neutron time-of-flight spectroscopy has been employed to study the crystal-field interaction in the pyrochlore titanate Ho2Ti2O7. The crystal-field parameters and corresponding energy-level scheme have been determined from a profile fit to the observed neutron spectra. The ground state is a well separated Eg doublet with a strong Ising-like anisotropy, which can give rise to frustration in the pyrochlore lattice. Using the crystal-field parameters determined for the Ho compound as an estimate of the crystal-field potential in other pyrochlore magnets, we also find the Ising type behavior for Dy. In contrast, the almost planar anisotropy found for Er and Yb prevents frustration, because of the continuous range of possible spin orientations in this case.

Study of Low Temperature Magnetic Properties of a Single Chain Magnet with Alternate Isotropic and Non-collinear Anisotropic Units

Here we study thermodynamic properties of an important class of single-chain magnets (SCMs), where alternate units are isotropic and anisotropic with anisotropy axes being non-collinear. This class of SCMs shows slow relaxation at low temperatures which results from the interplay of two different relaxation mechanisms, namely dynamical and thermal. Here anisotropy is assumed to be large and negative, as a result, anisotropic units behave like canted spins at low temperatures; but even then simple Ising-type model does not capture the essential physics of the system due to quantum mechanical nature of the isotropic units. We here show how statistical behavior of this class of SCMs can be studied using a transfer matrix (TM) method. We also, for the first time, discuss in detail how weak inter-chain interactions can be treated by a TM method. The finite size effect is also discussed which becomes important for low temperature dynamics. At the end of this paper, we apply this technique to study a real helical chain magnet.

A 10 tesla table-top controlled waveform magnet

Controlled waveform magnets (CWMs) are a class of pulsed magnets whose pulse shape with time can be programmed by the user. With a CWM, the user gains control not only over the magnitude of the field but also over its rate of change. In this work we present a table-top CWM, driven by a capacitor bank, capable of producing virtually any user-shaped magnetic field waveform up to 10 tesla. Insulated gate bipolar transistor chips have been paralleled to form the high current switch and paralleled chips of SiC Schottky diodes form the crowbar diode module. Sample controlled waveforms including flat-tops up to 10 tesla and some triangular magnetic field pulses have been successfully generated for 10-20 ms with a ripple < 1%. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.3699316]

Development of moving magnet type linear motor for dual piston compressor for pulse tube cryocooler

This paper describes the design, fabrication and testing of a moving magnet type linear motor of dual piston configuration for a pulse tube cryocooler for ground applications. Eight radially magnetized segmented magnets were used to form one set of a magnet ring. Four magnet rings of such type were constructed, in which one pair of rings has north-pole on its outer diameter and south-pole on inner diameter, while the other pair is it's complementary. The magnets were mounted with opposite poles together on the magnet holder with an axial moving shaft having a piston mounted on both ends of the shaft. The shaft movement was restricted to the axial direction by using C-clamp type flexures, mounted on both sides of the shaft. The force requirement for driving the compressor was calculated based on which the electrical circuit of motor is designed by proper selection of wire gauge and Ampere-turns. The flexure spring force estimation was done through simulation using ANSYS 11.0 and was verified experimentally; while the magnet spring force was determined experimentally. The motor with mounted piston was tested using a variable voltage and variable frequency power supply capable of driving 140 watts of load.

Single-ion magnet behaviour of heptacoordinated Fe(II) complexes: on the importance of supramolecular organization

Supramolecular organization of a metal complex may significantly contribute to the magnetization dynamics of mononuclear SMMs. This is illustrated for a heptacoordinated Fe(II) complex with rather moderate Ising-type anisotropy for which a slow magnetization relaxation with significant energy barrier was reached when this complex was properly organized in the crystal lattice. Incidentally, it is the first example of single-ion magnet behaviour of Fe(II) in a pentagonal bipyramid surrounding.

Magnet loturak: bezero-zerbitzari API baten garapena

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Optimum Magnetic Circuit Configurations for Permanent Magnet Aerospace Generators

In the design of high-speed low-power electrical generators for unmanned aircraft and spacecraft, maximization of specific output (power/weight) is of prime importance. Several magnetic circuit configurations (radial-field, axial-field, flux-squeezing, homopolar) have been proposed, and in this paper the relative merits of these configurations are subjected to a quantitative investigation over the speed range 10 000–100000 rev/min and power range 250 W-10 kW. The advantages of incorporating new high energy-density magnetic materials are described. Part I deals with establishing an equivalent circuit for permanent-magnet generators. For each configuration the equivalent circuit parameters are related to the physical dimensions of the generator components and an optimization procedure produces a minimum volume design at discrete output powers and operating speeds. The technique is illustrated by a quantitative comparison of the specific outputs of conventional radial-field generators with samarium cobalt and alnico magnets. In Part II the specific outputs of conventional, flux-squeezing, and claw-rotor magnetic circuit configurations are compared. The flux-squeezing configuration is shown to produce the highest specific output for small sizes whereas the conventional configuration is best at large sizes. For all sizes the claw-rotor configuration is significantly inferior. In Part III the power densities available from axial-field and flux-switching magnetic circuit configurations are maximized, over the power range 0.25-10 kW and speed range 10 000–100000 rpm, and compared to the results of Parts I & II. For the axial-field configuration the power density is always less than that of the conventional and flux-squeezing radial-field configurations. For the flux-switching generator, which is able to withstand relatively high mechanical forces in the rotor, the power density is again inferior to the radial-field types, but the difference is less apparent for small (low power, high speed) generator sizes. From the combined results it can be concluded that the flux-squeezing and conventional radial-field magnetic circuit configurations yield designs with minimum volume over the power and speed ranges considered. © 1985, IEEE. All rights reserved.