L. T. Tsymbal

Magnetic and structural properties of spin-reorientation transitions in orthoferrites

Magnetic and structural characteristics of ErFeO3, TmFeO3, and YbFeO3 single crystals were studied over a wide temperature range. Magnetic measurements found that the spin-rotation transitions in all crystals are well described by the earlier proposed theory with no fitting parameters. Additionally, they have shown the absence of the magnetic compensation point in TmFeO3 and a noticeable growth of the c-axis magnetization at low temperatures in TmFeO3 and ErFeO3. The x-ray measurements found no symmetry-lowering lattice distortions during the reorientation. Overall, the measurements cover a wide range of material parameters and demonstrate the generality of the modified mean field theory of the Γ4→Γ24→Γ2 orientation phase transitions in orthoferrites.

Measurements of spin reorientation in YbFeO3 and comparison with modified mean-field theory

Precise measurements of YbFeO_3 magnetization in the spin-reoirentation temperature interval are performed. It is shown that ytterbium orthoferrite is well described by a recently developed modified mean field theory developed for ErFeO_3. This validates the conjecture about the essential influence of the rare earth ions anisotropic paramagnetism on the magnetization behavior in the reorientation regions of all orthoferrites with Gamma{4} ->Gamma{24} ->Gamma{2} phase transitions.

Natural behavior of the magnetization under spontaneous reorientation: TmFeO3, ErFeO3

A SQUID magnetometer is used to study the behavior of the magnetization of TmFeO3 single crystals along the a and c principal crystallographic axes in the Γ4–Γ24–Γ2 spin reorientation range. The temperature dependences are obtained as the moduli of the magnetization vector M and its turn angle θ in the reorientation range. The results are compared with the same results for ErFeO3. It is shown that even though the experimental dependences |M|(T) and θ(T) are qualitatively different in TmFeO3 and ErFeO3 they can all be convincingly described on the basis of a modified mean-field theory previously proposed by the authors. Since the theoretical analysis does not include any parameters which are not known from experiment, the agreement between theory and experiment confirms that the model proposed for describing Γ4–Γ24–Γ2 phase transitions in orthoferrites is a general model. Dedicated to E. S. Borovik—Scientist and Humanitarian “Who can say what influence the silent presence of one person has on another?” Wal...

Magnetic Hysteresis in ErFeO

Magnetic hysteresis of ErFeO3 is investigated in the temperature interval between the compensation point T comp = 46 K and erbium ordering transition at T 12 = 4.1 K. The shape of the hysteresis loops evolves from rectangular near the compensation point to a double-triangle loops (similar to perminvar loops) near the erbium ordering transition. The evolution of the loop shape explains the peculiar temperature hysteresis observed at constant applied field.

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Magnetic hysteresis is studied in the orthoferrites ErFeO3 and TmFeO3 using the single crystal samples of millimeter dimensions. It is shown that in both materials one observes a temperature transition manifesting itself through the temperature hysteresis of the magnetic moment and a peculiar temperature evolution of the field hysteresis loop shapes near this transition. Experiments rule out the hypothesis that the ordering of the orthoferrite’s rare-earth magnetic moments plays an important role in these phenomena. The hysteresis curves can be explained by a few-domain magnetic state of the samples that results from the weak ferromagnetism of the orthoferrites. The phenomenon is generic for weak ferromagnets with temperature dependent magnetization. A large characteristic magnetic length makes the behavior of the relatively big samples analogous to that observed in the nanosize samples of strong ferromagnets.

Near the Low Temperature Erbium Ordering Transition

The results of a detailed theoretical analysis of coupling of weakly damped electromagnetic and acoustic waves in metals are presented. The main difference between the natures of coupling of modes propagating in the same (helicon–phonon resonance) or opposite (doppleron– phonon resonance) directions is established. The dispersion curves are split in the former case and bound in the latter case. As a result, a gap appears in the spectrum of coupled modes in the collisionless limit, both modes being soundlike. It is shown that in the case of doppleron–phonon resonance, inductive as well as deformative interaction of electrons with the lattice must be taken into account.

Mechanisms of magnetic and temperature hysteresis in ErFeO3 and TmFeO3 single crystals

We have investigated the thermal expansivities of an ErFeO3 single crystal along the three crystallographic orientations using a high-resolution capacitance dilatometer and found clear signatures of lattice distortions in the spin rotation region as evidence for strong spin-lattice coupling. The observed lattice strain is consistent with the smooth rotation of the magnetization and it reveals the importance of the magnetoelastic interaction. Heat capacity measurements show a well-defined plateau-like enhancement in the spin re-orientation regime as predicted by the Landau theory of second order phase transitions. The data are used to estimate microscopic anisotropy parameters. Heat capacity is also measured near the low-temperature erbium magnetic ordering transition.

Coupling of electromagnetic and acoustic modes in metals

A non-traditional point of view to the nature of anomalous skin effect is proposed on the basis of an analysis of the problem of coupling modes in the electron plasma of a metal. It is shown that the anomalous skin effect in an applied magnetic field is in fact the result of interaction and coupling of a number of intrinsic electromagnetic modes excited due to nonlocal effects and specific properties of doppleron modes. It is proved that the magnetic field dependence of anomalous skin effect is determined by the shape of the Fermi surface of the metal and that the classical anomalous skin effect in the model of free electrons is just a special case.

Lattice strain and heat capacity anomalies at the spin reorientation transitions of ErFeO3 orthoferrite

The magnetization and coercive field of Fe3BO6 with a special focus on the behavior near the transition point was studied. Magnetization measurements were performed on an Oxford Instruments VSM magnetometer. Magnetic moment was determined from the hysteresis loops which were typically square-shaped. One clearly sees the abrupt disappearance of the magnetization in one direction and appearance of magnetization in another direction at the transition point. The change in the absolute value of the magnetization is ascribed to the change of the sublattice canting angle