[en] Short communication

[en] Full Text: Ferromagnetism has been known for millenia, and has underpinned many technologies for centuries. The possibility of antiferromagnetism has only been noted in the last century. I show that far from being a footnote in condensed matter physics, antiferromagnetism is at the frontier of physics and is beginning to display genuine technological relevance

[en] The random exchange antiferromagnetic Heisenberg spin-1 chain at finite temperature is studied using a renormalization-group method. We follow the evolution of the bond probability distribution and calculate the free energy of the system. The spurious results found for the free energy shows that the standard renormalization group approach used for spin-((1)/(2)) chains does not guarantee the existence of the random singlet phase in the random spin-1 chain even in the presence of strong disorder

[en] Classical Heisenberg antiferromagnet on the pyrochlore lattice is studied using the nonequilibrium relaxation method. Effects of farther neighbor interactions are investigated. We found two ordered phases stabilized by the second- and the third-neighbor interactions.One is a commensurate phase where both k=0 mode and k=π mode appear. It occurs when J₃ is more ferromagnetic than J₂. The other one is a double-incommensurate phase which is characterized by two incommensurate wave numbers. It occurs when J₂ is more ferromagnetic than J₃. No long range ordered state is realized when J₂=J₃

[en] I consider the class of 'depleted pyrochlore' lattices of corner-sharing triangles, made by removing spins from a pyrochlore lattice such that every tetrahedron loses exactly one. Previously known examples are the 'hyperkagome' and 'kagome staircase'. I give criteria in terms of loops for whether a given depleted lattice can order analogous to the kagome √3√3 state, and also show how the pseudo-dipolar correlations (due to local constraints) generalize to even the random depleted case.

[en] Fast reversal processes in magnetic particles and arrays involve fundamental magnetic dynamic and relaxation processes. Exchange and dipolar interactions determine equilibrium ground states and strongly influence linear and nonlinear dynamics. Calculations are used to show how high frequency resonances in arrays of densely packed magnetic particles can affect reversal times, possibly leading to dramatic decreases in switching rates. High frequency excitations and dynamic processes in interface exchange coupled magnets are also discussed, with emphasis on exchange biased materials. The exchange bias effect is closely related to interface magnetic structure and magnetization processes in systems of ferromagnets exchange coupled to antiferromagnets. It is shown how magnetization processes in the antiferromagnet can be studied through observation of dynamic effects in the ferromagnetic component. [copyright] 2001 American Institute of Physics

[en] We study relaxation phenomena in the ferromagnetically ordered state of the Ising-like Heisenberg kagome antiferromagnets. We introduce the weathervane loop in order to characterize macroscopic degenerate ordered states and study the microscopic mechanism of the slow relaxation from a viewpoint of the dynamics of the weathervane loop configuration. This mechanism may give a possible origin of the slow relaxation reported in recent experiments

[en] FeCrAs undergoes a magnetic ordering transition at T_N ≃ 125 K. The magnetic structure of FeCrAs, which crystallizes in space group P6¯2m and is isostructural to Fe2P, was determined by constant wavelength neutron powder diffraction. A single basis function was found to describe the intensity distribution in the magnetic satellite reflections, which are associated with propagation vector k = (1/3, 1/3, 0), representing a K-point zone-boundary ordering. The magnetic intensity could be modelled by moments from Cr only, which lie on the 3g-sites, in pyramidal coordination by As, whereas the moments on Fe, in tetrahedral coordination on the 3f-sites, were found to be so small as to be zero within error. This agrees with previous Mossbauer spectroscopy measurements on this compound. The magnetic structure is characterized by non-collinear antiferromagnetic order of the moments, all of which lie in the hexagonal plane. This does not appear to have been observed in other monopnictides with Fe_2P structure but is consistent with geometric frustration of antiferromagnetic interactions. (author)

[en] The nonlinear dynamics of spin waves in antiferromagnetic with weak ferromagnetism has been considered in the present article. The sequential microscopic analysis of spin chains at the presence of nonsymmetric exchange and transition to quasi classics has been carried out. The soliton solutions for the equation of classical antiferromagnetic with weak ferromagnetism have been found.

[en] Some exact dynamic and static solutions of Landau-Lifshitz equations in antiferromagnets and ferromagnets found in this work. These solutions can be used for describing distribution of order parameter in small magnetic particles