arXiv subjects

I. A. Gudim

Publications and source records attributed to I. A. Gudim.

12 recordsLinked to original sources

arXiv2026

Terahertz optical activity near crystal field transitions of Tm3+ ions in magnetoelectric alumoborates

Crystal field (CF) excitations in the ground multiplet $^3H_6$ of Tm$^{3+}$ ions were investigated using terahertz transmission spectra of magnetoelectric TmAl$_3$(BO$_3$)$_4$ and Tm$_{0.05}$Yb$_{0.1}$Y$_{0.85}$Al$_3$(BO$_3$)$_4$. These excitations were identified as mainly magnetic dipole transitions from the ground singlet A$_1$ to the next excited doublet E, split by the crystal field of the D$_3$ symmetry. The fine structure of the modes was resolved at low temperatures. It manifested differently in lightly doped and in pure Tm borates, consistent with different distortions of the local crystal field with the D$_3$ symmetry. Strong natural optical activity was observed near the CF transitions resulting in a polarization plane rotation up to 25 degrees. The optical activity is quantitatively described by contributions of magnetic and electric dipole transitions to dynamic magnetoelectric susceptibility and taking into account the classification of local distortions.

cond-mat.mtrl-sci↗

arXiv2025

First-Order Spin-Reorientation Transition and Incomplete Softening of the Antiferromagnetic Resonance Mode in Multiferroic GdFe$_3$(BO$_3$)$_4$

The multiferroic ferroborate GdFe$_3$(BO$_3$)$_4$ with huntite-type structure exhibits magnetic ordering below T$_N$ = 38 K and contains two magnetic subsystems associated with Gd and Fe ions. Competing anisotropies of these subsystems drive a spin reorientation transition at T$_{SR}$ = 10.7 K, switching the ground state from easy-axis to easy-plane. Using antiferromagnetic resonance, we investigate the spin dynamics across this transition. The observed incomplete softening of a magnon mode during both field- and temperature-induced spin-reorientation transitions indicates the first-order nature of the phase transition, which is accompanied by a discontinuous jump in the effective anisotropy field. We reproduce this behavior using a simple model that attributes the jump in the anisotropy field to the presence of an effective fourth-order anisotropy constant, responsible for the discontinuous character of the transition. Remarkably, for in-plane magnetic fields, we identify a new AFMR mode that persists from 12 K up to T$_N$. This mode likely corresponds to the dynamics of a long period incommensurate state, previously detected by resonant elastic X-ray scattering.

cond-mat.str-el↗

arXiv2023

Features of synthesis of TbCr$_3$(BO$_3$)$_4$ single crystals by solution-melt method

The phase formation of terbium chromium borate in melt solutions based on bismuth trimolybdate and lithium tungstate was studied. It was shown that there is no trigonal phase of terbium chromium borate in a system based on bismuth trimolybdate at all component ratios. The ratio of components of a system based on lithium tungstate has been found, at which trigonal TbCr$_3$(BO$_3$)$_4$ crystals are formed at temperatures above 1100$^\circ$C, and below this temperature only a monoclinic phase is formed. The X-ray properties of the grown crystals were studied.

cond-mat.mtrl-sci↗

arXiv2022

Low-Temperature Magnetic Susceptibility of Erbium Aluminum Borate Single Crystal: Van Vleck Paramagnetism and Spin Correlations

Temperature dependencies of magnetic susceptibility in a trigonal single crystal of erbium aluminum borate were measured in the temperature range of 2 - 15 K at the external field of 100 Oe applied along the second- and third-order crystallographic axes. Analysis of the experimental data allows to identify the Van Vleck contribution to the susceptibility. The influence of spin correlations on the magnetic susceptibility has been identified. It has been estimate the negative paramagnetic Curie-Weiss temperature.

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

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

Spectroscopy of f-f transitions, crystal-field calculations, and magnetic and quadrupole helix chirality in DyFe$_3$(BO$_3$)$_4$

Recently, quadrupole helix chirality and its domain structure was observed in resonant x-ray diffraction experiments on DyFe$_3$(BO$_3$)$_4$ using circularly polarized x rays [T. Usui et al., Nature Materials 13, 611 (2014)]. We show that this effect can be explained quantitatively by calculating the quadrupole moments of the Dy$^{3+}$ ions induced by the low-symmetry ($C_2$) crystal-field (CF) component. In this work, the CF parameters for the Dy$^{3+}$ ions in the $P3_121$ ($P3_221$) phase of DyFe$_3$(BO$_3$)$_4$ are obtained from CF calculations based on the analysis of high-resolution temperature-dependent optical spectroscopy data. We also consider the helix chirality of the single-site magnetic susceptibility tensors of the Dy$^{3+}$ ions in the paramagnetic $P3_121$ ($P3_221$) phase and suggest a neutron diffraction experiment to reveal it.

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

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

Magnetic Phase Transitions in the NdFe_3(BO_3)_4 multiferroic

Low temperature studies of the behavior of the sound velocity and attenuation of acoustic modes have been performed on a single crystal NdFe_3(BO_3)_4. Transitions of the magnetic subsystem to the antiferromagnetically ordered state at T_N \approx 30.6 K have been revealed in the temperature behavior of the elastic characteristics. The features in the temperature behavior of elastic characteristics of the neodymium ferroborate and its behavior in the external magnetic field, applied in the basic plane of the crystal, permit us to suppose that the transition to an incommensurate spiral phase is realized in the system. This phase transition behaves as the first order one. H-T phase diagrams for the cases H \parallel a and H \parallel b have been constructed. The phenomenological theory, which explains observed features, has been developed.

cond-mat.str-el↗

arXiv2009

Crystal growth and magnetic properties of Nd1-xDyxFe3(BO3)4

Data about stability areas of Nd1-xDyxFe3(BO3)4 trigonal phases in fluxes on the bismuth trimolibdate basis and feature of labile phase dynamics conditions is noted. Group growth conditions of these phases single crystals on seeds and at spontaneous nucleation in a thin layer of flux on crystal carrier are described. Temperature and field dependences of magnetization and a specific heat for crystals with x = 0,1 and x = 0,25 are analyzed. The conclusion, that unlike easy plane NdFe3(BO3)4 antiferromagnetic and easy axis DyFe3(BO3)4 ones, spontaneous spin-flop transitions are inherent in these single crystals is resulted and it is connected with mutual influence of rare-earth subsystems through the common Fe-subsystem with strong exchange interaction. The anisotropies competition exerts essential influence on induced by field H parallel c3 magnetic phase transitions too.

cond-mat.mtrl-sci↗

arXiv2007

Magnetization and specific heat of TbFe3(BO3)4: Experiment and crystal field calculations

We have studied the thermodynamic properties of single-crystalline TbFe3(BO3)4. Magnetization measurements have been carried out as a function of magnetic field (up to 50 T) and temperature up to 350K with the magnetic field both parallel and perpendicular to the trigonal c-axis of the crystal. The specific heat has been measured in the temperature range 2-300K with a magnetic field up to 9 T applied parallel to the c-axis. The data indicate a structural phase transition at 192 K and antiferromagnetic spin ordering at 40 K. A Schottky anomaly is present in the specific heat data around 20 K, arising due to two low-lying energy levels of the Tb3+ ions being split by f-d coupling. Below TN magnetic fields parallel to the c-axis drive a spin-flop phase transition, which is associated with a large magnetization jump. The highly anisotropic character of the magnetic susceptibility is ascribed mainly to the Ising-like behavior of the Tb3+ ions in the trigonal crystal field. We describe our results in the framework of an unified approach which is based on mean-field approximation and crystal-field calculations.

cond-mat.other↗