Magnonic momentum transfer force on domain walls confined in space

Momentum transfer from incoming magnons to a Bloch domain wall is calculated using one dimensional continuum micromagnetic analysis. Due to the confinement of the wall in space, the dispersion relation of magnons is different from that of a single domain. This mismatch of dispersion relations can result in reflection of magnons upon incidence on the domain wall, whose direct consequence is a transfer of momentum between magnons and the domain wall. The corresponding counteraction force exerted on the wall can be used for the control of domain wall motion through magnonic linear momentum transfer, in analogy with the spin transfer torque induced by magnonic angular momentum transfer.Comment: 5 pages, 3 figure, published versio

Magnonic band structure of domain wall magnonic crystals

Magnonic crystals are prototype magnetic metamaterials designed for the control of spin wave propagation. Conventional magnonic crystals are composed of single domain elements. If magnetization textures, such as domain walls, vortices and skyrmions, are included in the building blocks of magnonic crystals, additional degrees of freedom over the control of the magnonic band structure can be achieved. We theoretically investigate the influence of domain walls on the spin wave propagation and the corresponding magnonic band structure. It is found that the rotation of magnetization inside a domain wall introduces a geometric vector potential for the spin wave excitation. The corresponding Berry phase has quantized value $4 n_w \pi$, where $n_w$ is the winding number of the domain wall. Due to the topological vector potential, the magnonic band structure of magnonic crystals with domain walls as comprising elements differs significantly from an identical magnonic crystal composed of only magnetic domains. This difference can be utilized to realize dynamic reconfiguration of magnonic band structure by a sole nucleation or annihilation of domain walls in magnonic crystals.Comment: 21 pages, 9 figure

Cambrian phosphatized fossils from southern China and their bearing on early metazoan evolution

Richly fossiliferous nodular and thin-bedded limestones of Lower and Middle Cambrian age are widespread in southern China, and contain abundant, diverse, and exceptionally well preserved fossils. By acid digestion of the limestones, numerous phosphatized shells displaying detailed three-dimensional characters have been isolated. The univalved ostracode larvae, displaying a univalved-bivalved transition, argue that univalved form may be a primitive larval character for shell-secreting crustaceans. The arthropod (possibly eodiscid trilobite) embryos with preserved blastomeres belong to two embryonic stages; the basic embryonic development of arthropods seems unchangeable with time. Cuticles of three palaeoscolecid worms display unique ornaments and body structures; their discovery reveals that wormlike organisms have achieved a high taxonomic diversity and a wide geographic distribution during the Early Cambrian. The description of redlichiid trilobite larvae and ontogenetic stages of Ichangia ichangensis Chang is of potential interests in recognizing the relationships among the oldest trilobite faunas. Morphological and functional analysis on especially long genal and axial spines of some rodiscids provodes key evidence to deduce their locomotion and life mode. Early instars of bradoriid ostracodes and eodiscid trilobites exhibit apparent morphological diversity, which seems to contrast with the traditional view that regards early development as conservative. However, a complex silicified sponge spicule assemblage associated with the Early Cambrian phosphatized fauna in Zhenping demonstrates that their conservative styles of body architecture were established quickly in the earliest Phanerozoic. These fossil Lagerstatten, as representatives of early skeletal metazoans, have displayed their primitive features without 'modification' relevant to adaptive radiation's of later times. Their morphological and ontogenetic data are therefore essential in evaluating the rapid diversification of early skeletal organisms and the phylogenetic relationships among major metazoan groups