151 research outputs found
Anomalous Hall effect in NiPt thin films
We study Hall effect in sputtered NixPt1-x thin films with different Ni
concentrations. Temperature, magnetic field and angular dependencies are
analyzed and the phase diagram of NiPt thin films is obtained. It is found that
films with sub-critical Ni concentration exhibit cluster-glass behavior at low
temperatures with a perpendicular magnetic anisotropy below the freezing
temperature. Films with over-critical Ni concentration are ferromagnetic with
parallel anisotropy. At the critical concentration the state of the film is
strongly frustrated. Such films demonstrate canted magnetization with the easy
axis rotating as a function of temperature. The magnetism appears via
consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather
than a single second-order phase transition. But most remarkably, the
extraordinary Hall effect changes sign at the critical concentration. We
suggest that this is associated with a reconstruction of the electronic
structure of the alloy at the normal metal - ferromagnet quantum phase
transition.Comment: 12 pages, 17 figure
Applications of p-deficiency and p-largeness
We use Schlage-Puchta's concept of p-deficiency and Lackenby's property of
p-largeness to show that a group having a finite presentation with p-deficiency
greater than 1 is large, which implies that Schlage-Puchta's infinite finitely
generated p-groups are not finitely presented. We also show that for all primes
p at least 7, any group having a presentation of p-deficiency greater than 1 is
Golod-Shafarevich, and has a finite index subgroup which is Golod-Shafarevich
for the remaining primes. We also generalise a result of Grigorchuk on Coxeter
groups to odd primes.Comment: 23 page
(Contravariant) Koszul duality for DG algebras
A DG algebras over a field with connected and
has a unique up to isomorphism DG module with . It is proved
that if is degreewise finite, then RHom_A(?,K): D^{df}_{+}(A)^{op}
\equiv D_{df}^{+}}(RHom_A(K,K)) is an exact equivalence of derived categories
of DG modules with degreewise finite-dimensional homology. It induces an
equivalences of and the category of perfect DG
-modules, and vice-versa. Corresponding statements are proved also
when is simply connected and .Comment: 33 page
Schreier rewriting beyond the classical setting
Using actions of free monoids and free associative algebras, we establish
some Schreier-type formulas involving the ranks of actions and the ranks of
subactions in free actions or Grassmann-type relations for the ranks of
intersections of subactions of free actions. The coset action of the free group
is used to establish the generalization of the Schreier formula to the case of
subgroups of infinite index. We also study and apply large modules over free
associative algebras in the spirit of the paper Olshanskii, A. Yu.; Osin, D.V.,
Large groups and their periodic quotients, Proc. Amer. Math. Soc., 136 (2008),
753 - 759.Comment: 17 page
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