Magnetic field induced intermediate state in dysprosium orthoferrite

The field induced spin reorientation in DyFeO₃ has been observed visually using the magneto-optical method. An intermediate state has been shown to exist between antiferromagnetic and weak ferromagnetic states. A simple model is proposed to calculate the static properties of phase domains.     

Nature of the morin transition in al-substituted hematite

The Mössbauer spectra of (Fe_1-cAl_c)2O3 with c=0.048 indicate the presence of two distinct spin phases below 245 K, one of which gradually disappears with increasing temperature. A careful study of the hyperfine parameters as a function of temperature reveals complex spin reorientation phenomena in both phases.     

Critical behaviour near the incommensurate-commensurate phase transition in dysprosium

Neutron scattering measurements of the helical turnangle indicate that the incommensurate-commensurate transition in Dy obeys a logarithmic mean-field behaviour and not a β-exponent power law.     

Investigations of the first order magnetic phase transition in dysprosium

The first order magnetic phase transition in polycrystalline sample of dysprosium (Dy) has been investigated in detail by dc-resistance vs. temperature (R-T) measurements. Distinct signature of coexistence of two magnetically ordered phases (i.e. ferromagnetic and antiferromagnetic), originating as a result of the metastable behavior associated with the first order phase transition (FOPT) is found near 90 K. By successfully recording the minor hysteresis loops within the hysteretic R-T regime of Dy, a varying degree of phase coexistence in the FOPT is demonstrated.     

Effect of a hard-magnetic surface layer in domain structures in the region of spontaneous spin-reorientation phase transition in erbium orthoferrite plates

The rearrangement of domain structures in erbium orthoferrite plates with a hard-magnetic surface layer has been visually investigated and explained on the basis of proposed physical models. It is shown that, when the temperature of such plates approaches the temperature range of spin reorientation, the surface energy density of the domain walls separating the internal and surface domains decreases, resulting in a transition to domain structures that are close to equilibrium.     

Faraday rotation and optical investigation of the metamagnetic phase transition in dysprosium phosphate

The metamagnetic phase transition in dysprosium phosphate has been studied by optical methods. A theoretical expression for the Faraday rotation in this substance is derived, and experimental results are reported for a long needle-shaped specimen. Observations of domains indicate that in DyPO₄ with magnetic field parallel to the crystallographic c-axis a mixed phase exists up to a tri-critical temperature T_t = 1.95 K.     

First-order phase transition in potassium dysprosium tungstate induced by the field renormalization and softening of the elastic moduli in the vicinity of a structural Jahn-Teller-type transition

The magnetostriction of KDy(WO₄)₂ single crystals is measured in an external magnetic field at temperatures below the temperature of a structural phase transition of the Jahn-Teller type. A steplike irreversible variation in the elastic strain is observed to occur with an increase in the magnetic field applied along the a or b axis of the monoclinic cell of the crystal. The residual change in the strain is retained after changing the sign of the magnetic field. The return to the initial state characterized by field-induced jumps in the strain is possible only after thermal cycling well above the structural phase transition temperature. The theory of this phenomenon is developed using a phenomenologically derived thermodynamic potential of the elastic sub-system that takes into account the crystal symmetry and the field renormalization of the elastic moduli. The jumplike transitions are interpreted as being due to the magnetic softening of the elastic moduli in the vicinity of the structural phase transition temperature.     

Thermodynamic model of the stabilization of an intermediate state in the region of the metamagnetic phase transition in erbium orthoferrite

The possible mechanisms of the thermodynamic stabilization of an intermediate state in the first-order metamagnetic phase transition in a magnetic field parallel to the Ising c axis of the Er³⁺ ions in erbium orthoferrite at T = 1.6 K have been analyzed. The model is chosen using the magneto-optical experimental data on the features of this state.     

On the order of the phase transition in KDA type ferroelectric crystals

The observation of a thermal hysteresis indicates that the phase transitions in KDA, KD²A, RDA and CDA crystals are of the first order. The static dielectric properties of these ferroelectrics resemble those of KD²P.     

On the type of a phase transition in the system of exciton polaritons in an optical microcavity

The type of a phase transition in the quasi-equilibrium system of exciton polaritons in a two-dimensional optical microcavity has been analyzed. It has been shown that, although the system contains two types of bosons undergoing mutual transformations into each other, only one phase transition to the superfluid state with the quasilong-range order occurs in the two-dimensional system. This phase transition is a Kosterlitz-Thouless phase transition. A new physical implementation—excitons in a photon crystal—has been proposed for the Bose condensation of exciton polaritons. The superfluid properties of the ordered phase are discussed, and the superfluid density and Kosterlitz-Thouless transition temperature have been calculated in the low-density approximation.     

Mössbauer studies of the morin transition in bulk and microcrystalline α-Fe2O32

Mössbauer spectra of bulk and microcrystalline hematite have been analyzed at the Morin transition for both the weak-ferromagnetic (WF) and anti-ferromagnetic (AF) phases simultaneously, increasing precision in the extracted Mössbauer parameters. The Morin transition in bulk took place in less than 0.4 K, and in the microcrystals decreased linearily with expanding lattice in agreement with its increase under external pressure. Temperature hysteresis measurements in the microcrystals gave values of the fourth-order magnetic anisotropy energy which indicated possible surface spin-pinning effects. In bulk the magnetic field decreased by 7 ± 0.5 kOe in going from the WF to the AF phase on decreasing temperature, and the isomer shift decreased by $\text{0.014 ± 0.003}\text{mm}\text{sec.}$ With lattice dilation the AF quadrupolar interaction appeared to decrease, while the isomer shift change across the transition goes positive. In contrast the change in magnetic field is not simply related to this lattice dilation, indicating surface spin-pinning effects.     

Ferromagnetic resonance in suspensions of cobalt-substituted magnetite

Colloids of cobalt-substituted magnetite are investigated using ferromagnetic resonance. It is found that the ferromagnetic resonance spectrum consists of two spectral lines. The intensity ratio of these lines depends on the size of the magnetic particles. The experimental results are interpreted in the framework of the Raikher-Stepanov theory. It is established that the average radius of particles increases with increasing time.     

External electric field effects in the resonant propagation of a TM- or TE-Type wave through an orthoferrite plate under the conditions of a Morin-type phase transition

Questions associated with the propagation of a TM- or TE-type bulk wave through a half-wave plate and arising due to the influence of crossed constant magnetic and electric fields are studied through the example of orthoferrite under the conditions of a Morin-type phase transition. The correspondence of resonant propagation conditions to both the spectrum of outgoing bulk magnetic layer polaritons and the spectrum of electromagnetic waves of a plate with extreme surface impedance is demonstrated.     

On the character of the Hartree-Fock-Bogoliubov solutions in a rotating frame

The nature of the solutions of the Hartree-Fock-Bogoliubov equations in a rotating frame is described. The significance of solutions which involve negative quasi-particle energy is discussed in detail.     

First order character of the B transition in liquid 3He

Measurements have been made of the discontinuous changes in entropy and static magnetization of liquid ³He at the B transition. These changes are related to previous measurement of the magnetic field dependence of this phase transition.     

A Mössbauer study of the morin transition on the surface and in the bulk of hematite single crystals

The Morin transition has been studied simultaneously by transmission and conversion electron Mössbauer spectroscopy on the surface and in the bulk of hematite single-crystal plates with orientation (111) and different origin. It was found that in both samples, the surface transition is shifted to higher temperatures with respect to the bulk.     

Solitary flexural waves on a supersonic domain wall in yttrium orthoferrite

Solitary flexural waves on a supersonic domain wall in yttrium orthoferrite are observed and investigated. These waves have a sharp leading edge and a protracted trailing edge, reminiscent of the waves accompanying moving vertical Bloch lines in iron garnet films. The total velocity of the solitary flexural waves in yttrium orthoferrites for all observed amplitudes equals the maximum velocity of the domain walls. Two solitary waves with identical amplitudes colliding head-on are annihilated. The waves possess topological charges, and they move and form dynamic profiles under the influence of gyroscopic forces. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 10, 760–765 (25 May 1997)