arXiv subjects

L. N. Bezmaternykh

Publications and source records attributed to L. N. Bezmaternykh.

At least 19 recordsLinked to original sources

arXiv2019

Thermal Conductivity and Magnetic Phase Diagram of CuB2O4

We have measured temperature and magnetic field dependences of the thermal conductivity along the c-axis, kc, and that along the [110] direction, k110, of CuB2O4 single crystals in zero field and magnetic fields along the c-axis and along the [110] direction. It has been found that the thermal conductivity is nearly isotropic and very large in zero field and that the thermal conductivity due to phonons is dominant in CuB2O4. The temperature and field dependences of kc and k110 have markedly changed at phase boundaries in the magnetic phase diagram, which has been understood to be due to the change of the mean free path of phonons caused by the change of the phonon-spin scattering rate at the phase boundaries. It has been concluded that thermal conductivity measurements are very effective for detecting magnetic phase boundaries.

cond-mat.str-el↗

arXiv2017

Switching of magnons by electric and magnetic fields in multiferroic borates

Electric manipulation of magnetic properties is a key problem of materials research. To fulfil the requirements of modern electronics, these processes must be shifted to high frequencies. In multiferroic materials this may be achieved by electric and magnetic control of their fundamental excitations. Here we identify magnetic vibrations in multiferroic iron-borates which are simultaneously sensitive to external electric and magnetic fields. Nearly 100% modulation of the terahertz radiation in an external field is demonstrated for SmFe3(BO3)4. High sensitivity can be explained by a modification of the spin orientation which controls the excitation conditions in multiferroic borates. These experiments demonstrate the possibility to alter terahertz magnetic properties of materials independently by external electric and magnetic fields.

cond-mat.mtrl-sci↗

arXiv2017

Evolution of Structure and Magnetic Properties of Cu2MnBO5 under Partial Mn3+->Fe3+ Substitution

Single crystals of Fe-substituted Cu2Mn1-xFexBO5 ludwigites have been synthesized using flux technique (x=0.2, 0.4, 0.5 - in the initial flux system). Structural properties of the synthesized compounds were studied by the single crystal and powder X-ray diffraction analysis. Obtained results were analyzed in the relationship with parent compound Cu2MnBO5. It was revealed that the type of monoclinic distortions of Fe-substituted ludwigites is different from the structure of Cu2MnBO5. The real cation composition and local structure of Cu2Mn1-xFexBO5 ludwigites were studied using XANES and EXAFS techniques, respectively. Analysis of field and thermal dependencies of magnetization showed a strong dependence of the magnetic properties of these ludwigites on x with changing the type of magnetic ordering.

cond-mat.mtrl-sci↗

arXiv2017

Effect of Fe-substitution on the structure and magnetism of single crystals Mn2-xFexBO4

Single crystalline Mn2-xFexBO4 with x = 0.3, 0.5, 0.7 grown by the flux method have been studied by means of X-ray diffraction and X-ray absorption spectroscopy at both Mn and Fe K edges. The compounds were found to crystallize in an orthorhombic warwickite structure (sp. gr. Pnam). The magnetization data have revealed a spin-glass transition at TSG= 11, 14 and 18 K for x= 0.3, 0.5 and 0.7, respectively.

cond-mat.mtrl-sci↗

arXiv2017

Giant gigahertz optical activity in multiferroic ferroborate

In contrast to well studied multiferroic manganites with a spiral structure, the electric polarization in multiferroic borates is induced within collinear antiferromagnetic structure and can easily be switched by small static fields. Because of specific symmetry conditions, static and dynamic properties in borates are directly connected, which leads to giant magnetoelectric and magnetodielectric effects. Here we prove experimentally that the giant magnetodielectric effect in samarium ferroborate SmFe3(BO3)4 is of intrinsic origin and is caused by an unusually large electromagnon situated in the microwave range. This electromagnon reveals strong optical activity exceeding 120 degrees of polarization rotation in a millimeter thick sample.

cond-mat.str-el↗

arXiv2017

Terahertz spectroscopy of crystal-field transitions in magnetoelectric TmAl3(BO3)4

Dynamic magnetic properties of magnetoelectric TmAl3(BO3)4 borate have been investigated by terahertz spectroscopy. Crystal field (CF) transitions within the ground multiplet 3H6 of Tm3+ ions are observed and they are identified as magnetic-dipole transitions from the ground singlet A1 to the next excited doublet E of Tm3+ ions. Unexpected fine structure of the transitions is detected at low temperatures. The new modes are assigned to local distortions of the sites with D3 symmetry by Bi3+ impurities, which resulted in the splitting of A1 -> E transition. Two types of locally distorted sites are identified and investigated. The main contribution to the static magnetic susceptibility is shown to be determined by the matrix elements of the observed magnetic transitions. We demonstrate that even in case of local distortions the symmetry of the undistorted crystal is recovered for magnetic and for quadratic magnetoelectric susceptibilities.

cond-mat.str-el↗

arXiv2016

Bifurcations observed in the spectra of coupled electron-phonon modes in multiferroic $PrFe_3(BO_3)_4$ subjected to a magnetic field

We report on bifurcations effect mediated by the electron-phonon coupling in a concentrated rare-earth-containing antiferromagnet, observed in the spectra of coupled $4f$-electron-phonon modes under the influence of an external magnetic field. The effect was observed in the low-temperature far-infrared (terahertz) reflection spectra of a multiferroic easy-axis antiferromagnet $PrFe_3(BO_3)_4$ in magnetic fields $\textbf{B}_{ext}||c$. Both paramagnetic and magnetically ordered phases (including a spin-flop one) were studied in magnetic fields up to 30 T. We show that the field behavior of the coupled modes can be successfully explained and modeled on the base of the equation derived in the frame of the theory of coupled electron-phonon modes, with the same field-independent electron-phonon interaction constant $|W| = 14.8 cm^{-1}$.

cond-mat.mtrl-sci↗

arXiv2015

Giant directional birefringence in multiferroic ferroborate

Many technological applications are based on electric or magnetic order of materials, for instance magnetic memory. Multiferroics are materials which exhibit electric and magnetic order simultaneously. Due to the coupling of electric and magnetic effects, these materials show a strong potential to control electricity and magnetism and, more generally, the properties and propagation of light. One of the most fascinating and counter-intuitive recent results in multiferroics is directional anisotropy, the asymmetry of light propagation with respect to the direction of propagation. The absorption in the material can be different for forward and backward propagation of light, which in extreme case may lead to complete suppression of absorption in one direction. Another remarkable effect in multiferroics is directional birefringence, i.e. different velocities of light for different directions of propagation. In this paper, we demonstrate giant directional birefringence in a multiferroic samarium ferroborate. The effect is easily observed for linear polarization of light in the range of millimeter-wavelengths, and survives down to very low frequencies. The dispersion and absorption close to the electromagnon resonance can be controlled and fully suppressed in one direction. Therefore, samarium ferroborate is a universal tool for optical control: with a magnetic field as an external parameter it allows switching between two functionalities: polarization rotation and directional anisotropy.

cond-mat.mtrl-sci↗

arXiv2015

Crystal and local atomic structure of Co-doped MgFeBO_4 warwickites

Single crystalline MgFeBO_4, Mg_0.5Co_0.5FeBO_4 and CoFeBO_4 have been grown by the flux method. The samples have been characterized by X-ray spectral analysis, X-ray diffraction and X-ray absorption spectroscopy. The X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra have been measured at the Fe andCoK-edges over a wide temperature range (6.5 - 300 K). The composition, the charge state and local environment of both Fe and Co atoms have been determined. The effects of Mg substitution by Co on the local structural distortions have been revealed experimentally and the M-O bond anisotropy has been found.

cond-mat.mtrl-sci↗

arXiv2015

Uniaxial anisotropy and low-temperature antiferromagnetism of Mn2BO4 single crystal

The Mn2BO4 single crystals have been grown using the flux technique. The careful study crystal structure and magnetic properties have been carried out. The antiferromagnet transition at TN = 26 K has been traced through the dc magnetization and specific heat temperature dependences. The magnetic uniaxial anisotropy has been detected with easy axis of magnetization lying in ab-plane. A reduction of the effective magnetic moment value is assigned to the non-quenched orbital moment of Jahn-Teller Mn3+ ions. Based on the superexchange interactions calculations the magnetic behavior is discussed.

cond-mat.str-el↗

arXiv2014

Antiferromagnetic dichroism and Davydov splitting of 3d-excitons in a complex multisublattice magnetoelectric CuB2O4

The space and time symmetry breaking at magnetic phase transitions in multiferroics results in a number of strongly pronounced optical effects. Our high-resolution spectroscopic study of 3d- excitons in a complex multi-sublattice magnetoelectric CuB2O4 demonstrates that, among those, a large antiferromagnetic linear dichroism is observed which is highly sublattice-sensitive to subtle changes in the spin subsystems. We prove that the discovered linear dichroism is related microscopically to the magnetic Davydov splitting of the exciton states. We announce a novel magnetic phase transition and argue that an elliptical spiral structure rather than a simple circular helix is realized in the incommensurate phase, these findings being overlooked in previous studies by optical and other techniques. We claim that this spectroscopic method can be effectively applied to other materials for revealing hidden features of magnetic structures and phase transitions.

cond-mat.mtrl-sci↗

arXiv2014

Splitting of a nondegenerate phonon mode in PrFe3(BO3)4: 4f crystal-field level between TO and LO phonon frequencies

A new effect originating from the crystal-field-excitation - phonon coupling was observed (in the far infrared spectra of a multiferroic PrFe3(BO3)4). The reststrahlen band corresponding to the A2 symmetry nondegenerate phonon mode near 50 cm-1 (1.5 THz) splits into two bands at about 100 K, well above TN = 32 K. These bands shift and narrow progressively with further lowering the temperature, demonstrating pronounced peculiarities at TN. The observed effects were explained by an interaction of the A2 phonon mode with the 4f crystal-field electronic excitation of Pr3+ whose frequency falls into the TO - LO frequency region of the phonon mode. Inversion of the TO and LO frequencies for the electronic excitation and a formation of coupled electron-phonon modes are discussed. Fitting of the TO frequency vs temperature experimental plots by theoretical curves revealed the value 14.6 cm-1 for the electron-phonon coupling constant.

cond-mat.mtrl-sci↗

arXiv2014

Field-Temperature Evolution of Antiferromagnetic Phases in Ludvigites Ni3-xMnxBO5

The conditions for the flux growth of new Mn-Ni oxyborates with the ludwigite structure are reported. Magnetic measurement data for the samples with nickel and manganese predominance are presented. Diamagnetic anomalies of the antiferromagnetic phases are established and analyzed in the framework of a model comprising two antiferromagnetically interacting subsystems, each being antiferromagnetically ordered.

cond-mat.mtrl-sci↗

arXiv2013

Ho and Fe magnetic ordering in multiferroic HoFe3(BO3)O4

Resonant and non-resonant X-ray scattering studies on HoFe3(BO3)O4 reveal competing magnetic ordering of Ho and Fe moments. Temperature and X-ray polarization dependent measurements employed at the Ho L3 edge directly reveal a spiral spin order of the induced Ho moments in the ab-plane propagating along the c-axis, a screw-type magnetic structure. At about 22.5 K the Fe spins are observed to rotate within the basal plane inducing spontaneous electric polarization, P. Components of P in the basal plane and along the c-axis can be scaled with the separated magnetic X-ray scattering intensities of the Fe and Ho magnetic sublattices, respectively.

cond-mat.str-el↗

arXiv2012

Magnetooptical Study of Spin-Orientation Phase Transition in $NdFe_3(BO_3)_4$ Single Crystal

The magnetic field dependences of birefringence in a $NdFe_3(BO_3)_4$ single crystal have been measured in the case where the direction of light propagation coincides with the trigonal crystal axis $C_3$ ($k\|C_3$), and the external magnetic field is oriented along the second-order axis $C_2$ ($H\|C_2$). In the temperature range, in which an incommensurate phase exists with the formation of a long-period antiferromagnetic helix, the strongly pronounced jumps in the field dependence of birefringence are revealed and identified as a firstorder spin-orientation phase transition. The phase transition was accompanied by a hysteresis in the field dependences of birefringence. The $H-T$ phase diagram for a $NdFe_3(BO_3)_4$ single crystal has been plotted in the case where the magnetic field is oriented along the crystal axis $C_2$ ($H\|C_2$).

cond-mat.mtrl-sci↗

arXiv2012

Magnetoelectricity in the system $RAl_3(BO_3)_4$ ($R$ = Tb, Ho, Er, Tm)

The magnetoelectric effect in the system $RAl_3(BO_3)_4$ ($R$ = Tb, Ho, Er, Tm) is investigated between 3 K and room temperature and at magnetic fields up to 70 kOe. We show a systematic increase of the magnetoelectric effect with decreasing magnetic anisotropy of the rare earth moment. A giant magnetoelectric polarization is found in the magnetically (nearly) isotropic $HoAl_3(BO_3)_4$. The polarization value in transverse field geometry at 70 kOe reaches 3600 $μC/m^2$ which is significantly higher than reported values for the field-induced polarization of linear magnetoelectric or even multiferroic compounds. The results indicate a very strong coupling of the f-moments to the lattice. They further indicate the importance of the field-induced ionic displacements in the unit cell resulting in a polar distortion and a change in symmetry on a microscopic scale. The system $RAl_3(BO_3)_4$ could be interesting for the technological utilization of the high-field magnetoelectric effect.

cond-mat.str-el↗

arXiv2011

Giant Magnetoelectric Effect in HoAl_3(BO_3)_4

A giant magnetoelectric polarization is found in HoAl$_3$(BO$_3$)$_4$. The polarization in transverse field geometry at 70 kOe reaches 3600 $μC/m^2$ which is significantly higher than reported values of linear magnetoelectric or even multiferroic compounds. The magnetostrictive effect is also measured and compared with the magnetoelectricity. The results show that spin-lattice coupling in HoAl$_3$(BO$_3$)$_4$ is extremely strong and that the magnetic field causes a large polar distortion of the ionic positions in the unit cell.

cond-mat.str-el↗

arXiv2010

Antiferromagnetic resonance in ferroborate NdFe$_3$(BO$_3$)$_4

The AFMR spectra of the NdFe$_3$(BO$_3$)$_4$ crystal are measured in a wide range of frequencies and temperatures. It is found that by the type of magnetic anisotropy the compound is an "easy-plane" antiferromagnet with a weak anisotropy in the basal plane. The effective magnetic parameters are determined: anisotropy fields $H_{a1}$=1.14 kOe and $H_{a2}$=60 kOe and magnetic excitation gaps $Δν_1$=101.9 GHz and $Δν_2$=23.8 GHz. It is shown that commensurate-incommensurate phase transition causes a shift in resonance field and a considerable change in absorption line width. At temperatures below 4.2 K nonlinear regimes of AFMR excitation at low microwave power levels are observed.

cond-mat.mtrl-sci↗