Theory Of Domain Structure Research Articles

On the Theory of Domain Structure of Disordered Ferroelectrics

We present a comprehensive analysis of domain structure formation in ferroelectric phase of incipient ferroelectrics with off-center dipole impurities like KTaO 3 :Li, Nb,Na. Our analysis is carried out on the base of effective free energy of disordered ferroelectrics, derived by us earlier. This free energy permits to apply the standard approach to domain structure calculation. Using coupled system of Maxwell equations with those obtained by minimization of above free energy, we calculate the physical characteristics of domain structure as functions of impurity dipoles concentration n. Our theory can be easily generalized for arbitrary temperature and crystal shape including thin films.

On the theory of domain structure in ferromagnetic phase of diluted magnetic semiconductors

We present a comprehensive analysis of domain structure formation in ferromagnetic phase of diluted magnetic semiconductors (DMS) of p-type. Our analysis is carried out on the base of effective magnetic free energy of DMS calculated by us earlier [Yu.G. Semenov, V.A. Stephanovich, Phys. Rev. B 67 (2003) 195203]. This free energy, substituting DMS (a disordered magnet) by effective ordered substance, permits to apply the standard phenomenological approach to domain structure calculation. Using coupled system of Maxwell equations with those obtained by minimization of above free energy functional, we show the existence of critical ratio ν cr of concentration of charge carriers and magnetic ions such that sample critical thickness L cr (such that at L < L cr a sample is monodomain) diverges as ν → ν cr . At ν > ν cr the sample is monodomain. This feature makes DMS different from conventional ordered magnets as it gives a possibility to control the sample critical thickness and emerging domain structure period by variation of ν. As concentration of magnetic impurities grows, ν cr → ∞ restoring conventional behavior of ordered magnets. Above facts have been revealed by examination of the temperature of transition to inhomogeneous magnetic state (stripe domain structure) in a slab of finite thickness L of p-type DMS. Our theory can be easily generalized for arbitrary temperature and DMS shape.

Magnetic anisotropy, first-order phase transition, and Brown’s paradox in rare-earth metals

The anomalous behavior of magnetization curves (first-order magnetization process, FOMP) of highly anisotropic rare-earth metal compounds was studied. It is pointed out that FOMP assignment to a large contribution from higher magnetic anisotropy constants Ki comes into conflict with the point-ion approximation of crystal field theory. An alternative interpretation based on the multisublattice model is proposed; this model makes use only of first-order sublattice constants kj derived from independent experimental NMR data. Direct calculations provide a satisfactory explanation of the FOMP in Tb2Fe17. A possible connection of the FOMP with Brown’s paradox in the theory of domain structure and coercive force is proposed.

Theory of domain structures and associated defects in the incommensurate phase of quartz

Theory of domain structures and associated defects in the incommensurate phase of quartz