A note on the theory of spin wave resonance in spiral structures

The appearance of two resonant modes of spin waves with different non-zero wave vectors is theoretically predicted for a magnetic arrangement of the type of an antiferromagnetic spiral combined with weak antiferromagnetism in the direction of the spiral axis. A study is made of the question of the Hamiltonian suitable for possible applications of the chosen magnetic arrangement, and the possibility of energetic stability of the considered magnetic structure for two concrete realistic forms of the Hamiltonian is pointed out.The author expresses his sincere thanks for valuable discussions and stimulating comments to Dr. S. Krupika and Dr. J. Loos, P. Novák and I. Veltruský of the Institute of Solid State Physics of the Czechoslovak Academy of Sciences, and to Assoc. Prof. J. Morkowski and Assoc. Prof. L. Kowalewski of the Polish Academy of Sciences and Poznan University.     

Transdisciplinary aspects of diffusion and magnetocaloric effect

The modeling of magnetocaloric effect (MCE) based on quasiparticle formalism was used to show a possibility to increase our knowledge of diffusion and phase transitions by a transdisciplinary scientific approach. Generalized understanding of diffusion and of some phase transitions was suggested. New relations between MCE and elastic parameters of materials, obtained from modeling procedure, were presented. The paper contains also the short discussion of a necessity to use hypercomplex mathematics in modeling of magnetic processes and specifically in a modeling of MCE. Some remarks concerning nanomaterials are added. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calculation of spin-wave energy and the mean value of Hamiltonian in a noncollinear magnetic sublattice structure by the method of Green's functions

The contribution of this work is the extension of Green's function formalism to the case of noncollinear, canted, 6-sublattice magnetic structure. The external magnetic field was considered. The selfconsistent procedure for calculation of renormalized spin-wave energies and the mean value of the Hamiltonian was discussed on the basis of both Tyablikov's and Callen's decoupling approximations and it was shown that the use of Callen's decoupling requires a preliminary solution of the problem on the basis of simpler decoupling. The equations are analogous to the Callen's equation but the temperature dependent factor has a more general form and instead of an explicit equation for energy there is an implicit equation.     

Noncollinear magnetic structure in a random system of densely packed hard spheres

For an amorphous model system consisting of a random set of 100 identical hard sphere densely packed in a cube with periodical boundary conditions the energies of spiral magnetic structures are investigated. It is shown for a simple model with exponentially decaying antiferromagnetic interaction that a spiral structure may exist displaying a minimum energy. The wavevector of the spiral minimizing the interaction energy depends on the range of interaction: for the short range one the pitch of the spiral is twice as high as that for the longer range of interactions The calculated energies are compared with the interaction energies in s.c., f.c.c., and b.c.c. lattices. It is found that the energy gain in the topologically random system with respect to the magnetically disordered state may be higher than that corresponding to the antiferromagnetic arrangement in a crystal.One of the authors (S. K.) thanks Dr. J. L. Finney for a valuable discussion concerning the computer generation of the random set of hard spheres.     

Influence of amorphous environment on magnetic structure

The influence of disordered medium on the magnetic structure of crystalline clusters is discussed. In a plate-like crystalline cluster with localized moments the disordered magnetic environment leads to preference of a spiral magnetic structure over the antiferromagnetic collinear ordering that would be otherwise realized. By the numerical solution of a specific model qualitative information was obtained about the influence of the exponential rate of decrease of the exchange interaction, plate thickness and degree of disorder of the medium on the magnetic structure of the cluster.     

Spin waves and magnetocaloric effect in two-sublattice antiferrimagnet

The magnetocaloric effect in the stable antiferrimagnetic phase of a two-sublattice uniaxial antiferrimagnet is studied on the basis of the spin wave theory. The negative slope in theH-dependence of the lowest spin-wave energy branch allows the cooling effect with increasing external magnetic fieldH. The dependence of the effect on the strength of exchange and anisotropy and the influence of phonons is discussed in detail.     

Multiple topologies from glycopolypeptide-dendron conjugate self-assembly: nanorods, micelles, and organogels

Glycopolypeptides (GPs) were synthesized by ring-opening polymerization of glycosylated N-carboxyanhydride monomer and attached to hydrophobic dendrons at one chain end by "click" reaction to obtain amphiphilic anisotropic macromolecules. We show that by varying polypeptide chain length and dendron generation, an organogel was obtained in dimethylsulfoxide, while nanorods and micellar aggregates were observed in aqueous solutions. Assemblies in water were characterized by electron microscopy and dye encapsulation. Secondary structure of the GP chain was shown to affect the morphology, whereas the chain length of the poly(ethylene glycol) linker between the GP and dendron did not alter rod-like assemblies. Bioactive surface chemistry of these assemblies displaying carbohydrate groups was demonstrated by interaction of mannose-functionalized nanorods with ConA.     

A remark on an anomaly of the spin-wave spectrum in spiral spin structures

It is shown that magnetic dipolar interaction gives rise to a discontinuity in the magnon dispersion relation for antiferromagnetic spiral spin structures. Some numerical results for the magnon energy in dysprosium are presented.     

Photo‐ and pH‐Responsive Polycarbonate Block Copolymer Prodrug Nanomicelles for Controlled Release of Doxorubicin

Photo/pH dual‐responsive amphiphilic diblock copolymers with alkyne functionalized pendant o‐nitrobenzyl ester group are synthesized using poly(ethylene glycol) as a macroinitiator. The pendant alkynes are functionalized as aldehyde groups by the azide‐alkyne Huisgen cycloaddition. The anticancer drug doxorubicin (DOX) molecules are then covalently conjugated through acid‐sensitive Schiff‐base linkage. The resultant prodrug copolymers self‐assemble into nanomicelles in aqueous solution. The prodrug nanomicelles have a well‐defined morphology with an average size of 20–40 nm. The dual‐stimuli are applied individually or simultaneously to study the release behavior of DOX. Under UV light irradiation, nanomicelles are disassembled due to the ONB ester photocleavage. The light‐controlled DOX release behavior is demonstrated using fluorescence spectroscopy. Due to the pH‐sensitive imine linkage the DOX molecules are released rapidly from the nanomicelles at the acidic pH of 5.0, whereas only minimal amount of DOX molecules is released at the pH of 7.4. The DOX release rate is tunable by applying the dual‐stimuli simultaneously. In vitro studies against colon cancer cells demonstrate that the nanomicelles show the efficient cellular uptake and the intracellular DOX release, indicating that the newly designed copolymers with dual‐stimuli‐response have significant potential applications as a smart nanomedicine against cancer.