Бистабильное и многодоменное состояния ферромагнитных микропроводов alpha-Fe/(PrDy)(FeCo)B

Microwire of α-Fe(50 at.%)(PrDy)(FeCo)B(48 at.%) was obtained by extracting a hanging melt drop of (PrDy)(FeCo)B in an electron beam. It was shown that a single microwire with a diameter of 50 μm and a length of 0.8 - 6 mm with an amorphous phase (PrDy)(FeCo)B content of ~ 48% and a polycrystalline α-Fe phase of ~ 52% has a rectangular narrow magnetic hysteresis loop and, accordingly, a bistable state with a switching field of ~ 100 Oe. The shortening of the wire to ~ 0.6 mm leads to a sharp deviation from the squareness of the loop, reducing the slope of the dependence of the magnetization on the field and the coercive force to 20 Oe. In the subsurface layers consisting of the amorphous phase (PrDy)(FeCo)B, oriented areas of reverse magnetization are observed. The role of the magnetic dipole interaction in the formation of a magnetic hysteresis loop of chaotic microwire assemblies of various compositions is discussed.

Конкуренция доменных стенок и фазы обратной намагниченности в магнитной релаксации спинового переключателя Pt/Co/Ir/Co/Pt

A multilayer Pt/Co/Ir/Co/Pt/GaAs heterostructures demonstrates a long term (to several hours) magnetic relaxation between two stable states of the magnetization of the system. The magnetization reversal of the heterostructure layers occurs both due to the formation of nuclei of the reverse magnetization domains and as a result of their further growth by means of motion of domain walls. The competition between two these processes provides a nonexponential character of the magnetic relaxation. At 300 K, the contributions of these processes to the relaxation are commensurable, while, at temperatures lower than 200 K, the contribution of the nucleation is suppressed and the magnetic relaxation occurs as a result of motion of the domain walls.

Rotational remagnetization and orientational transitions in submicron YIG films

It is shown that for the quasinormal remagnetization of the submicron YIG films with the normal along the [111] axis, which are in the single-domain state, two types of orientation transitions (OT) due to the influence of easy axes can be distinguished. The nonreciprocity of the FMR spectrum for forward and reverse magnetization due to the influence of easy axes is shown.

Heat Treatment Design for NdFe and SmCo5 Magnets with Basis on the Phase Diagram

The high coercivity region of the Nd-Fe-B and Sm-Co phase diagrams is discussed. Slow cooling heat treatments may eliminate lattice defects, which are responsible for nucleation of reverse magnetization. The concept of diffusion length can be used for the design of heat treatments. Analytical formulas for calculation of the diffusion length as function of the cooling rate of the heat treatment are presented.

The Critical Volume for Nucleation

In magnets based in phases with high magnetocrystalline anisotropy like Nd2Fe14B or SmCo5 there is a competition between magnetostatic energy and domain wall energies. If the grain size is large, the formation of domain walls is energetically favorable. When the formation of domain walls is an unfavorable process, coercivity is larger. A better comprehension of this phenomenon is possible if the energy necessary for the first domain wall formation is properly evaluated. To address this problem, the magnetostatic energy of a sphere magnetized in two opposite directions, separated by a domain wall, is calculated using Legendre Polynomials. The data allow the determination of the reversible volume for nucleation. It is predicted a “recoil effect”, the magnetization may be reversible until a given volume of reverse magnetization.

Carnivora from the late Early Pleistocene of Cal Guardiola (Terrassa, Vallès-Penedès Basin, Catalonia, Spain)

The paleontological site of Cal Guardiola (UTM 31T DG1702), on the western bank of the Torrent de Vallparadís (Terrassa, Catalonia, Spain), was discovered in early 1997 during the construction of a socio-sanitary building next to the Mútua de Terrassa. A report on the geology and stratigraphy of Cal Guardiola was published by Berástegui et al. (2000), including a preliminary report on the fauna. This preliminary study suggested an estimated age for Cal Guardiola of ca. 1.0 Ma (Berástegui et al., 2000). Unpublished paleomagnetic analyses, carried out by Miguel Garcés, indicate a reverse magnetization for the sampled sediments, which can be correlated to below the Brunhes-Matuyama geomagnetic boundary (pers. com. of M. Garcés in Postigo Mijarra et al., 2007), thus being older than 0.8 Ma. This dating roughly corresponds to the later part of the Epivillafranchian biochron (1.2 to 0.9 Ma), which in Europe is best represented by the faunal assemblages from Untermassfeld in Germany, Le Vallonnet in France, and Colle Curti and Slivia in Italy (Palombo et al., 2008 and references therein). The faunal assemblage from Cal Guardiola represents one of the latest Epivillafranchian faunas from Europe and thus deserves particular attention for unraveling the chronology of the dispersal events that took place during the Epivillafranchian-Galerian turnover. However, thus far only the primate remains from Cal Guardiola have been published (Alba et al., 2008), while the rest of the fauna remains unpublished. Here we describe the carnivore remains from Cal Guardiola, which record one of the latest occurrences of the hyenidPachycrocutain Europe and further attests the coexistence of two distinct ursid lineages by the latest Early Pleistocene in Europe.