How a ferromagnet drives an antiferromagnet in exchange biased CoO/Fe(110) bilayers.

Antiferromagnet/ferromagnet (AFM/FM) bilayers that display the exchange bias (EB) effect have been subjected to intensive material research, being the key elements of novel spintronics systems. In a commonly accepted picture, the antiferromagnet, considered as a rigid material due to its high anisotropy and magnetic hardness, controls the magnetic properties of the ferromagnet, such as a shift of the hysteresis loop or coercivity. We show that this AFM-FM master-slave hierarchy is not generally valid and that the influence of the ferromagnet on the magnetic anisotropy (MA) of the neighbouring antiferromagnet must be considered. Our computer simulation and experimental studies of EB in an epitaxial CoO/Fe(110) bilayer show that the ferromagnetic layer with strong uniaxial magnetic anisotropy determines the interfacial spin orientations of the neighbouring AFM layer and rotates its easy axis. This effect has a strong feedback on the EB effect experienced by the FM layer. Our results show new physics behind the EB effect, providing a route for grafting a desired anisotropy onto the AFM and for precise tailoring of EB in AFM/FM systems.

Kinetics of drug decomposition. Part 74. Kinetics of degradation of minocycline in aqueous solution.

Under anaerobic conditions within the pH range 0.38-9.35 (at 343 K) and in the presence of air oxygen within the pH range 0.83-5.42 (at 323 K) the degradation of minocycline (MC) in aqueous solutions follows the first order kinetics. In neutral and alkaline solutions in the presence of air oxygen the autocatalytic first order reaction takes place. The degradation of MC both under anaerobic and aerobic conditions is catalyzed by buffer components of formate, acetate, phosphate and borate buffers. Under anaerobic conditions the degradation of MC is a result of water evoked spontaneous reaction. The rate of this reaction depends on the charge of MC. The specific rate constants of degradation for particular ionic species of MC under anaerobic conditions have been determined. The rate of oxidation of MC is also charge-dependent. The most susceptible to oxidation are the ionic species MC+-, MC+-- and MC--. Effects of temperature, metal ions and stabilizers on the stability of MC were also investigated.

Kinetics of drug decomposition. Part XXXVI. Stability of 10-(1'-methyl-4'-piperazinylpropyl)-phenothiazine derivatives on the grounds of kinetics of thermal degradation and Hammett equation.

Thermal degradation of aqueous and buffered solutions of perazine, prochlorperazine, trifluoperazine, thioproperazine, thiethylperazine and butaperazine salts was examined by kinetic method using an accelerated testing of pharmaceutical preparations. The order, rate constants and activation parameters (Q100, E, delta H not equal to, delta S not equal to, delta G not equal to ) of the reaction given were discussed. The predicted stability of the examined derivatives was compared on the grounds of a calculated time t10% and K293 kappa. A dependence between the stability and kind of substituent in the C2 positions was discussed in terms of the Hammett equation.

Kinetics of drug decomposition. Part 37. Kinetics of autoxidation of narcotine in aqueous solutions.

The overall apparent first-order rate constants for the reaction of autoxidation of Narcotine (NC) - k1 and Cotarnine (CT) - k2 and the rate constants for autoxidation of the protonated (ks) and undissociated (kb) forms have been determined. The kinetic equation for the reaction of autoxidation at constant concentration of NC, CT and the atmospheric oxygen depending on the pH of the reaction medium has been established as: k1 = ks([H+]/([H+]+K'a))+kb(K'a/([H+]+K'a), k2=(ks[H+]+K'a))+kb (K'a/([H+]+K'a) (1+1+1/kt+1K)). The following thermodynamic parameters for the rate constants ks and kb have been calculated: deltaH not equal to, log A and deltaS not equal to.

Kinetics of drug decomposition. Part 45. Logk--pH profile for rolitetracycline degradation.

UV spectrophotometry and fluorometry were applied for an examination of rolitetracycline (RT) degradation at pH's ranged from ca 0-8 to 13-0. It was demonstrated that these methods enable to follow the rate of degradation of tetracycline formed in the course of RT hydrolysis. However, they do not allow to monitor the hydrolysis of RT to tetracycline. Application of the so-called "subtraction technique" permits to calculate the rate constants for the total, reversible epimerization reaction and for the subsequent degradation of the resultant products. A rate equation derived for RT degradation in an alkaline medium beginning at pH 10-5 contains a term second-order in the hydroxide ion. Such a relationship was not yet observed in the course of an antibiotic degradation.