The relation of the rotational hysteresis integral with the magnetization switching mode is experimentally analysed in materials which are subjected to different treatments which can modify the ...magnetization switching mode. As expected, the value of the integral depends on the basic processes of magnetization. They evolve with the evolution of the switching in the expected way, both when the switching changes from wall motion to rotation of the magnetization, and when, in single-domain particles, the rotation occurs with different reversal modes.
The distribution of anisotropy fields in Ba ferrite particles and its evolution with the addition of Co/Ti ions is studied. The width of the anisotropy distribution increases with increase in doping ...content, and further is larger at low temperature. The result is ascribed to the role of the shape anisotropy, the effect of which is enhanced by doping and decreasing temperature.
Single-spin asymmetries in the semi-inclusive production of charged pions in deep-inelastic scattering from transversely and longitudinally polarized proton targets are combined to evaluate the ...subleading-twist contribution to the longitudinal case. This contribution is significantly positive for π+ mesons and dominates the asymmetries on a longitudinally polarized target previously measured by Hermes. The subleading-twist contribution for π− mesons is found to be small.
A measurement of the proton spin structure function g1p(x,Q{sup 2}) in deep-inelastic scattering is presented. The data were taken with the 27.6 GeV longitudinally polarised positron beam at HERA ...incident on a longitudinally polarised pure hydrogen gas target internal to the storage ring. The kinematic range is 0.021<x<0.85 and 0.8 GeV{sup 2}<Q{sup 2}<20 GeV{sup 2}.
The Gerasimov-Drell-Hearn (GDH) sum rule connects the anomalous contribution to the magnetic moment of the target nucleus with an energy-weighted integral of the difference of the helicity-dependent ...photoabsorption cross sections. Originally conceived for real photons, the GDH integral can be generalised to the case of photons with virtuality Q2. For spin-1/2 targets such as the nucleon, it then represents the non-perturbative limit of the first moment \(\Gamma_1\) of the spin structure function g1(x,Q2) in deep inelastic scattering (DIS). The data collected by HERMES with a deuterium target are presented together with a re-analysis of previous measurements on the proton. This provides an unprecedented and complete measurement of the generalised GDH integral for photon-virtuality ranging over 1.2<Q2<12.0 GeV2 and for photon-nucleon invariant mass squared W2 ranging over 1<W2<45 GeV2, thus covering simultaneously the nucleon-resonance and the deep inelastic scattering regions. These data allow the study of the Q2-dependence of the full GDH integral, which is sensitive to both the Q2-evolution of the resonance form factors and contributions of higher twist. The contribution of the nucleon-resonance region is seen to decrease rapidly with increasing Q2. The DIS contribution is sizeable over the full measured range, even down to the lowest measured Q2. As expected, at higher Q2 the data are found to be in agreement with previous measurements of the first moment of g1. From data on the deuteron and proton, the GDH integral for the neutron has been derived and the proton-neutron difference evaluated. This difference is found to satisfy the fundamental Bjorken sum rule at Q2 = 5 GeV2.
Measurements of the individual multiplicities of \(\pi^+, \pi^-\) and \(\pi^0\) produced in the deep-inelastic scattering of 27.5 GeV positrons on hydrogen are presented. The average charged pion ...multiplicity is the same as for neutral pions, up to \(z \approx 0.7\), where z is the fraction of the energy transferred in the scattering process carried by the pion. This result (below \(z \approx 0.7\)) is consistent with isospin invariance. The total energy fraction associated with charged and neutral pions is \(\rm 0.51 \pm 0.01 (stat.) \pm 0.08\) (syst.) and \(\rm 0.26 \pm 0.01 (stat.) \pm 0.04 (syst.)\), respectively. For fixed z, the measured multiplicities depend on both the negative squared four momentum transfer \(Q^2\) and the Bjorken variable x. The observed dependence on \(Q^2\) agrees qualitatively with the expected behaviour based on NLO-QCD evolution, while the dependence on x is consistent with that of previous data after corrections have been made for the expected \(Q^2\)-dependence.
Hard exclusive electroproduction of π+π− pairs off hydrogen and deuterium targets has been studied by the HERMES experiment at DESY. Legendre moments 〈P1〉 and 〈P3〉 of the angular distributions of π+ ...mesons in the center-of-mass frame of the pair have been measured for the first time. Their dependence on the π+π− invariant mass can be understood as being due to the interference between relative P-wave (isovector) and S-, D-wave (isoscalar) states of the two pions. The increase in magnitude of 〈P1〉 as Bjorken x increases is interpreted in the framework of generalized parton distributions as an enhancement of flavour non-singlet qq¯ exchange for larger values of x, which leads to a sizable admixture of isoscalar and isovector pion pairs. In addition, the interference between P-wave and D-wave states separately for transverse and longitudinal pion pairs has been studied. The data indicate that in the f2(1270) region at 〈Q2〉=3 GeV2 higher-twist effects can be as large as the leading-twist longitudinal component.
The temperature dependence of coercivity for (Ti,Co)-substituted barium ferrites between 77 and 500 K is found to be substantially different from that of nonsubstituted material. This difference can ...be accounted for by a much steeper decrease of the magnetocrystalline anisotropy field component and by the possibility that the magnetization reversal mechanism varies from coherent to incoherent as the temperature is varied.< >
A new type of uniaxial particles for magnetic recording whose precursors are produced via an original hydrothermal process was recently introduced in the market. The characterizing feature of these ...materials is their extremely uniform size and ellipsoidal shape. Most of their properties can be ascribed to the lack of external (pores, dendrites, sharp edges) as well as internal (because of ellipsoidal shape) - self-demagnetizing sources, which suggests the name of "Non-Polar (NP)" particles. As a result of this morphology, they show unique magnetic properties. The magnetization reversal mechanism is not accounted for by any known mechanism as fanning or curling and the rotational hysteresis gives very sharp W r vs. H curves with the lowest values for the integral ever measured for particulate media. The behaviour of coercivity versus packing fraction for Cobalt-surface-modified NP particles is described by a new "constricted magnetization" model. The reasons for these unique characteristics and the practical impact that these materials may have in the field of magnetic recording are discussed.
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