I. V. Yatsyk

Determination of the region of existence of ferromagnetic nanostructures in the paraphase of La1−xBaxMnO3 by the EPR method

In the paraphase of a number of La1−xBaxMnO3 single crystals with 0.1 ≤ x ≤ 0.2 below 340 K, signals of the ferromagnetic resonance are observed, which indicates the presence of magnetically ordered nanoscopic objects (ferrons). The region of the existence of ferrons on the Ba density-temperature phase diagram has an approximate triangular shape, which is characteristic of the Griffiths phase. Investigations of the angular and frequency dependences of the position of the ferromagnetic resonance line indicate that the nanostructures have a spherical shape. The parameters of their magnetic anisotropy are found to be Ha1 = 2500 Oe and Ha2 = −700 Oe.

Abrupt changes in the temperature dependence of the ESR linewidth of La1 − x Cax MnO3 single crystals

The temperature dependence of the ESR linewidth in La1 − x Cax MnO3 single crystals with various dopant concentrations (x = 0.18, 0.2, 0.22, 0.25, and 0.3) has been studied. An abrupt decrease in the ESR linewidth has been observed in the samples with a dopant concentration of x = 0.18 and 0.2 near the respective temperatures TOO′ ≈ 260 and 240 K of the orthorhombic to pseudocubic structural phase transition. The abrupt decrease in the ESR linewidth by approximately 180 Oe has been also observed in the whole temperature range when the concentration is increased from x = 0.2 to x = 0.22. The formula for the fourth moment of the ESR line has been derived including both crystal fields and isotropic exchange interactions and taking into account the difference between the exchange coupling of a spin to its nearest in-plane and out-of-plane neighbors. The formula has been used to estimate the parameter D of the crystalline field on Mn3+ ions.

Electron paramagnetic resonance studies of GdMnO3 single crystal and thin film deposited onto a LaAlO3 substrate

Electronic paramagnetic resonance (EPR) spectra of a GdMnO3 single crystal and GdMnO3/LaAlO3 thin film have been measured at X- and Q-band frequencies in the temperature range from 4.2 to 300 K. It is found that the EPR spectrum of a GdMnO3 single crystal consists of only one broad exchange-narrowed line. Unusual magnetism is observed at the interface between the GdMnO3 thin film and LaAlO3 substrate, where it is possible to see the fine structure of the EPR spectrum for a Gd3+ ion. The parameters characterizing the fine structure related to the Gd3+ ion in the GdMnO3 film deposited onto the LaAlO3 substrate are determined.

EPR spectra of a GdMnO3 thin film on a SrTiO3 substrate

Electron paramagnetic resonance (EPR) spectra of a GdMnO3/SrTiO3 thin film in the X band have been measured in the temperature interval from 200 to 450 K. Signals from two types of paramagnetic centers have been observed in the spectra. The first paramagnetic center is a subsystem of Gd3+ ions, in the EPR spectrum of which the fine structure lines are resolved below 350 K. The second paramagnetic center is a system of manganese and gadolinium ions, in the EPR spectrum of which an exchange-narrowed line is observed with the width ΔH several times less than the width ΔH of an exchange-narrowed line observed in the GdMnO3 single crystal. Unusual magnetic properties are due to the mismatch of the lattice parameters of the GdMnO3 thin film and the SrTiO3 substrate.

ESR and Mössbauer Spectroscopic Study of Sr-Doped Ytterbium Ferromanganites

In this paper, we have studied the crystal structure of strontium-substituted manganite and ytterbium ferromanganites Yb0.82Sr0.18Mn1 – xFexO3 (x = 0–0.2) by using X-ray diffraction analysis. Magnetic microstructure has been studied by electron paramagnetic resonance and nuclear gamma-resonance (Mössbauer) spectroscopy. We have observed phase separation in the ceramics for antiferromagnetic, superparamagnetic, and ferromagnetic phases.

EPR-Determined Anisotropy of the g -Factor and Magnetostriction of a Cu 2 MnBO 5 Single Crystal with a Ludwigite Structure

Electron paramagnetic resonance (EPR) and magnetostriction of the Cu2MnBO5 single crystal have been studied. The EPR spectrum consists of a single Lorentzian line due to the exchange-coupled system of spins of Cu2+ and Mn3+ ions. It has been established experimentally that the g-factor in the paramagnetic region is strongly anisotropic and anomalously small, which is not typical of the exchange-coupled system of spins of Cu2+ and Mn3+ ions. At a temperature of 150 K, the g-factors along the crystallographic a, b, and c axes are 2.04, 1.96, and 1.87, respectively. Such small effective g-factor values can be due to the effect of the anisotropic Dzyaloshinskii–Moriya exchange interaction between the spins of Cu2+ and Mn3+ ions directed along the a axis. The presence of two Cu2+ and Mn3+ Jahn–Teller ions occupying four nonequivalent positions in the crystal is responsible for the absence of the inversion center. It is found that the behavior of the magnetostriction of Cu2MnBO5 is not typical of transition-metal crystals but is closer to the behavior of crystals containing rare-earth ions.

Oscillation of the multiferroic/ferroelectric GdMnO3/SrTiO3 and YbMnO3/SrTiO3 interfaces in the EPR spectrum

The electron paramagnetic resonance (EPR) method was used to study thin manganite ytterbium YbMnO3 and gadolinium GdMnO3 films, with a thickness of 100 nm, deposited on a SrTiO3 virtual ferroelectric backing (GdMnO3/SrTiO3 and YbMnO3/SrTiO3). The most interesting results are obtained in the 40–100 K temperature interval for GdMnO3/SrTiO3, and 40–150 K for YbMnO3/SrTiO3. In these temperature ranges, in addition to the exchange-narrowed line from all film material, absorbed power oscillations were observed in the EPR spectra, with the amplitude of the oscillations depending on both the temperature and the magnitude of the external magnetic field.

Temperature features of the EPR spectrum of GdMnO3: Single crystal and thin film GdMnO3/LaAlO3

Electron paramagnetic resonance (EPR) spectra of GdMnO3 single crystal and GdMnO3/LaAlO3 thin film are measured at Q-band frequency in the temperature range of 4.2 to 300 K. The temperature dependence of parameters of the spin Hamiltonian corresponding to the monoclinic symmetry of such paramagnetic centers as Gd3+ ions in the GdMnO3/LaAlO3 film is determined.