arXiv subjects

S. V. Demishev

Publications and source records attributed to S. V. Demishev.

At least 19 recordsLinked to original sources

arXiv2024

Anisotropy of exchange interactions in honeycomb ladder compound ReCl5

The Re5+(5d2) compounds possess large spin-orbital interaction which urges for large anisotropy, non-collinear structures and other phenomena. Here we present ReCl5 composed by separate Re2Cl10 units formed by edge-shared chlorine octahedra. It demonstrates the formation of antiferromagnetically ordered state in two steps at TN1 = 35.5 K and TN2 = 13.2 K seen in dc-, ac-magnetic susceptibility and in specific heat. At 4K it can be transformed to the state with spontaneous magnetic moment by relatively weak magnetic field m0H = 0.5 T via metamagnetic phase transition. Ab initio calculations give anisotropic ferromagnetic exchange interactions J1 and J2 within and between rhenium pairs forming the zig-zag chains along the a-axis. Pairs of zig-zag chains are coupled by ferromagnetic interaction J3 along the c-axis into magnetic honeycomb ladders. The ladders are coupled by significantly weaker interaction J4.

cond-mat.mtrl-sci↗

arXiv2024

Evidence for spin droplets (ferrons) formation in the heavy fermion metal CeB$_6$ with dynamic charge stripes

The presented studies of resistivity (R), thermal conductivity (k) and specific heat (C) at low temperature 1.8-7 K in magnetic field up to 90 kOe made it possible to detect for the first time the exponential field dependences R(H), 1/k(H), $C(H) \sim \exp(-μ_{\rm eff}H/kBT)$ of the charge transport and thermal characteristics in the so-called antiferroquadrupole (AFQ) phase of the archetypal heavy-fermion CeB$_6$ hexaboride. From magnetoresistance measurements it is shown that in the AFQ state the effective magnetic moment varies in the range $μ_{\rm eff}(T) = 1.4$-1.9$μ$B, and its value is very close to $μ_{\rm eff}(τ)(T) = 2μ$B, derived from the field dependence of the relaxation time $|tau(H)$ observed in the heat capacity and thermal conductivity experiments. The phenomenological model proposed here allowed us to attribute the magnetic moments to spin droplets (ferrons), that appear in the bulk AFQ phase of CeB$_6$ crystals. The relevant electron phase separation at the nanoscale, manifested by dynamic charge stripes, that leads to the formation of ferrons, was revealed from the analysis of low-temperature X-ray diffraction experiments using the maximum entropy method. We argue that the Jahn-Teller collective mode of B$_6$ clusters is responsible for the charge stripe formation, which subsequently induces transverse quasi-local vibrations of Ce ions in the form of pairs and triples. These lead to 4f-5d spin fluctuations providing spin-polarons (ferrons) in the CeB$_6$ matrix.

cond-mat.str-el↗

arXiv2019

Maltese Cross anisotropy in Ho0.8Lu0.2B12 antiferromagnetic metal with dynamic charge stripes

The model strongly correlated electron system Ho0.8Lu0.2B12 which demonstrates a cooperative Jahn-Teller instability of the boron sub-lattice in combination with rattling modes of Ho(Lu) ions, dynamic charge stripes and unusual antiferromagnetic (AF) ground state has been studied in detail at low temperatures by magnetoresistance, magnetization and heat capacity measurements. Based on received results it turns out that the angular H-fi-T magnetic phase diagrams of this non-equilibrium AF metal can be reconstructed in the form of a Maltese cross. The dramatic AF ground state symmetry lowering of this dodecaboride with fcc crystal structure can be attributed to the redistribution of conduction electrons which leave the RKKY oscillations of the electron spin density to participate in the dynamic charge stripes providing with extraordinary changes in the indirect exchange interaction between magnetic moments of Ho3+ ions and resulting in the emergence of a number of various magnetic phases. It is also shown that the two main contributions to magnetoresistance in the complex AF phase, the (i) positive linear on magnetic field and the (ii) negative quadratic component can be separated and analyzed quantitatively, correspondingly, in terms of charge carrier scattering on spin density wave (5d) component of the magnetic structure and on local 4f-5d spin fluctuations of holmium sites.

cond-mat.str-el↗

arXiv2018

Observation of dynamic charge stripes in Tm0.19Yb0.81B12 at the metal-insulator transition

Higher accuracy low temperature charge transport measurements in combination with precise X-ray diffraction experiment have allowed detecting the symmetry lowering in the single domain Tm0.19Yb0.81B12 crystals of the family of dodecaborides with metal-insulator transition. Basing on the fine structure analysis we discover formation of dynamic charge stripes within the semiconducting matrix of Tm0.19Yb0.81B12. The charge dynamics in these metallic nano-size conducting channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 10^11 Hz) of quantum motion of the charge carriers. It is suggested that caused by cooperative Jahn-Teller effect in the boron sub-lattice, the large amplitude rattling modes of the Tm and Yb ions are responsible for modulation of the conduction band along [110] direction through the variation of 5d-2p hybridization of electron states.

cond-mat.str-el↗

arXiv2016

Magnetic field dependence of the neutron spin resonance in CeB6

In zero magnetic field, the famous neutron spin resonance in the f-electron superconductor CeCoIn5 is similar to the recently discovered exciton peak in the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5 into two components, indicating that it is a doublet. Here we employ inelastic neutron scattering (INS) to scrutinize the field dependence of spin fluctuations in CeB6. The exciton shows a markedly different behavior without any field splitting. Instead, we observe a second field-induced magnon whose energy increases with field. At the ferromagnetic zone center, however, we find only a single mode with a non-monotonic field dependence. At low fields, it is initially suppressed to zero together with the antiferromagnetic order parameter, but then reappears at higher fields inside the hidden-order phase, following the energy of an electron spin resonance (ESR). This is a unique example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR and INS consistently over a broad range of magnetic fields.

cond-mat.str-el↗

arXiv2016

Magnetization of the Mn$_{1-x}$Fe$_x$Si in high magnetic field up to 50 T: possible evidence of a field-induced Griffiths phase

Magnetic properties of single crystals of Mn$_{1-x}$Fe$_x$Si solid solutions with $x < 0.2$ are investigated by pulsed field technique in magnetic fields up to 50 T. It is shown that magnetization of Mn$_{1-x}$Fe$_x$Si in the paramagnetic phase follows power law $M(B) \sim B^α$ with the exponents $α\sim 0.33-0.5$, which starts above characteristic fields $B_c \sim 1.5-7$ T depending on the sample composition and lasts up to highest used magnetic field. Analysis of magnetization data including SQUID measurements in magnetic fields below 5 T suggests that this anomalous behavior may be likely attributed to the formation of a field-induced Griffiths phase in the presence of spin-polaron effects.

cond-mat.str-el↗

arXiv2015

Suppression of Superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ : Evidence of Static Magnetic Moments Induced by Non-Magnetic Impurities

Based on low temperature resistivity, heat capacity and magnetization investigations we show that the unusually strong suppression of superconductivity in Lu$_x$Zr$_{1-x}$B$_{12}$ BSC-type superconductors in the range $x$$<$0.08 is caused by the emergence of static spin polarization in the vicinity of non-magnetic lutetium impurities. The analysis of received results points to a formation of static magnetic moments with $μ_{eff}$$\approx$$3μ_B$ per Lu-ion. The size of these spin polarized nanodomains was estimated to be about 5 $Å$.

cond-mat.str-el↗

arXiv2015

Scrutinizing Hall effect in Mn$_{1-x}$Fe$_{x}$Si: Fermi surface evolution and hidden quantum criticality

Separating between ordinary (OHE) and anomalous (AHE) Hall effect in the paramagnetic phase of Mn$_{1-x}$Fe$_{x}$Si reveals OHE sign inversion associated with the hidden quantum critical (QC) point $x^*\sim0.11$. The semimetallic behavior at intermediate Fe content leads to verifiable predictions in the field of fermiology, magnetic interactions and QC in Mn$_{1-x}$Fe$_{x}$Si. The change of electron and hole concentrations is considered as a driving force for tuning the QC regime in Mn$_{1-x}$Fe$_{x}$Si via modifying of RKKY exchange interaction within the Heisenberg model of magnetism.

cond-mat.str-el↗

arXiv2015

Macroscopic evidence of skyrmion lattice inhomogeneity and magnetic vortex states in the A-phase of MnSi

The magnetic inhomogeneity of the A-phase in MnSi chiral magnet is identified for the first time from the precise measurements of transverse magnetoresistance (MR) anisotropy. The area inside the A-phase (A-phase core) corresponds to isotropic MR having no confinement to the MnSi crystal lattice. Per contra, the MR becomes anisotropic both on the border of the A-phase and in other magnetic phases, the strongest magnetic scattering being observed when external magnetic field applied along [001] or [00-1] directions. We argue here that the established MR features prove the presence of two different types of the skyrmion lattices inside the A-phase, and the dense skyrmion state of the A-phase core is built from individual skyrmions similar to Abrikosov-type magnetic vortexes.

cond-mat.str-el↗

arXiv2014

Charge transport in Ho$_x$Lu$_{1-x}$B$_{12}$: Separating Positive and Negative Magnetoresistance in Metals with Magnetic Ions

The magnetoresistance (MR) $Δρ/ρ$ of cage-glass compound Ho$_x$Lu$_{1-x}$B$_{12}$ with various concentration of magnetic holmium ions ($x$$\leq$0.5) has been studied in detail concurrently with magnetization M(T) and Hall effect investigations on high quality single crystals at temperatures 1.9-120 K and in magnetic field up to 80 kOe. The undertaken analysis of $Δρ/ρ$ allows us to conclude that the large negative magnetoresistance (nMR) observed in vicinity of Neel temperature is caused by scattering of charge carriers on magnetic clusters of Ho$^{3+}$ ions, and that these nanosize regions with AF exchange inside may be considered as short range order AF domains. It was shown that the Yosida relation $-Δρ/ρ$$\sim$$M^2$ provides an adequate description of the nMR effect for the case of Langevin type behavior of magnetization. Moreover, a reduction of Ho-ion effective magnetic moments in the range 3-9$μ_B$ was found to develop both with temperature lowering and under the increase of holmium content. A phenomenological description of the large positive quadratic contribution $Δρ/ρ$$\sim$$μ_D^2 H^2$ which dominates in Ho$_x$Lu$_{1-x}$B$_{12}$ in the intermediate temperature range 20-120 K allows to estimate the drift mobility exponential changes $μ_D$$\sim$$T^{-a}$ with $a$=1.3-1.6 depending on Ho concentration. An even more comprehensive behavior of magnetoresistance has been found in the AF state of Ho$_x$Lu$_{1-x}$B$_{12}$ where an additional linear positive component was observed and attributed to charge carriers scattering on the spin density wave (SDW). High precision measurements of $Δρ/ρ=f(H,T)$ have allowed us also to reconstruct the magnetic H-T phase diagram of Ho$_{0.5}$Lu$_{0.5}$B$_{12}$ and to resolve its magnetic structure as a superposition of 4f (based on localized moments) and 5d (based on SDW) components.

cond-mat.str-el↗

arXiv2014

Magnetization scaling in the paramagnetic phase of Mn1-xFexSi solid solutions

The magnetization field and temperature dependences in the paramagnetic phase of Mn1-xFexSi solid solutions with x<0.3 are investigated in the range B<5 T and T<60 K. It is found that field dependences of the magnetization M(B,T=const) exhibit scaling behavior of the form B\partial M/\partial B-M=F(B/(T-Ts)), where Ts denotes an empirically determined temperature of the transition into the magnetic phase with fluctuation driven short-range magnetic order and F(\c{hi}) is a universal scaling function for given composition. The scaling relation allowed concluding that the magnetization in the paramagnetic phase of Mn1-xFexSi is represented by the sum of two terms. The first term is saturated by the scaling variable \c{hi}=B/(T-Ts), whereas the second is linearly dependent on the magnetic field. A simple analytical formula describing the magnetization is derived and applied to estimates of the parameters characterizing localized magnetic moments in the studied system. The obtained data may be qualitatively interpreted assuming magnetic inhomogeneity of the paramagnetic phase on the nanoscale.

cond-mat.str-el↗

arXiv2011

Spin excitations of the correlated semiconductor FeSi probed by THz radiation

By direct measurements of the complex optical conductivity $σ(ν)$ of FeSi we have discovered a broad absorption peak centered at frequency $ν_{0}(4.2 K) \approx 32 cm^{-1}$ that develops at temperatures below 20 K. This feature is caused by spin-polaronic states formed in the middle of the gap in the electronic density of states. We observe the spin excitations between the electronic levels split by the exchange field of $H_{e}=34\pm 6 T$. Spin fluctuations are identified as the main factor determining the formation of the spin polarons and the rich magnetic phase diagram of FeSi.

cond-mat.str-el↗

arXiv2011

Hall effect in the vicinity of quantum critical point in Tm1-xYbxB12

The angular, temperature and magnetic field dependences of Hall resistance roH for the rare-earth dodecaboride solid solutions Tm1-xYbxB12 have been studied in a wide vicinity of the quantum critical point (QCP) xC~0.3. The measurements performed in the temperature range 1.9-300 K on high quality single crystals allowed to find out for the first time in these fcc compounds both an appearance of the second harmonic contribution in ro2H at QCP and its enhancement under the Tm to ytterbium substitution and/or with increase of external magnetic field. When the Yb concentration x increases a negative maximum of a significant amplitude was shown to appear on the temperature dependences of Hall coefficient RH(T) for the Tm1-xYbxB12 compounds. Moreover, a complicated activation type behavior of the Hall coefficient is observed at intermediate temperatures for x>0.5 with activation energies Eg~200K and Ea~55-75K in combination with the sign inversion of RH(T) at low temperatures in the coherent regime. The density of states renormalization effects are analyzed within the variation of Yb concentration and the features of the charge transport in various regimes (charge gap formation, intra-gap manybody resonance and coherent regime) are discussed in detail in Tm1-xYbxB12 solid solutions.

cond-mat.str-el↗

arXiv2010

Hall effect in PrB$_6$ and NdB$_6$

Hall effect was studied on the single crystals of antiferromagnets PrB$_6$ and NdB$_6$ at temperatures 2K$<$T$<300$K in magnetic fields up to 8T using the sample rotation technique. At low magnetic fields $μ_0$H$\leq1$T Hall coefficient R$_\mathrm{H}$, which is practically temperature independent in paramagnetic state at 8K$\leq$T$\leq70$K, is characterized by the values of R$_H$(PrB$_6$)$\sim-(4.2\pm0.1)\cdot10^{-4}$ cm$^3$/C and R$_H$(NdB$_6$)$\sim-(4.1\pm0.1)\cdot10^{-4}$ cm$^3$/C. Rather different behaviour of R$_H$ is observed in antiferromagnetic (AF) phases of these hexaborides. For PrB$_6$ the decrease of temperature below T$_N\approx6.7$K is accompanied by a noticeable ($ΔR_H/R_H\sim10%$) elevation of R$_H$($μ_0$H$=1$T) to the values of $-(3.8\pm0.1)\cdot10^{-4}$ cm$^3$/C. On the contrary, the low field Hall coefficient in NdB$_6$ diminishes by about 15% reaching the value R$_H\approx-(4.7\pm0.1)\cdot10^{-4}$ cm$^3$/C in AF state at 2.5K. The increase of magnetic field inducing magnetic transition in the commensurate magnetic phase of PrB$_6$ results in essential R$_H$ changes (up to 10%) at liquid helium temperatures. The anomalous behaviour of the charge transport parameters for RB$_6$ (R=Pr, Nd) found in vicinity of Neel temperature suggests the possible effect of $5d$-states spin density polarization of both in AF and paramagnetic states of the compounds under investigation.

cond-mat.str-el↗

arXiv2006

New polarization effect and collective excitation in S=1/2 quasi 1D antiferromagnetic quantum spin chain

Anomalous polarization characteristics of magnetic resonance in CuGeO3 doped with 2% of Co impurity are reported. For the Faraday geometry this mode is damped for the microwave field Bw aligned along a certain crystallographic direction showing that the character of magnetic oscillation differs from the standard spin precession. The observed resonance coexists with the ESR on Cu2+ chains and argued not to be caused by "impurity" EPR, as previously claimed, but to correspond to a previously unknown collective mode of magnetic oscillations in S=1/2 AF quantum spin chain.

cond-mat.str-el↗

arXiv2006

High frequency study of the orbital ordering resonance in the strongly correlated heavy fermion metal CeB6

We report results of the study of the recently discovered magnetic resonance in the orbitally ordered phase of CeB6 (the orbital ordering resonance) in a wide frequency range 44-360 GHz. It is found that the g-factor for this resonance increases with frequency from g(44 GHz)~1.55 to g(>250 GHz)~1.7. In addition to the orbital ordering resonance for the frequencies exceeding 200 GHz a new magnetic resonance with the g-factor 1.2-1.3 is detected.

cond-mat.str-el↗

arXiv2006

ESR Probing of Quantum Critical Phenomena in Doped S=1/2 AF Quantum Spin Chain

The results of high frequency (60-315 GHz) studies of the ESR in CuGeO3 single crystals containing 0.9% of the Mn impurity are reported. The quantitative ESR line shape analysis shows that the low temperature (T<40 K) magnetic susceptibility of Cu2+ chains diverges with the critical exponent a=0.81 and therefore indicates an onset of a quantum critical (QC) regime. The scenario, in which disorder caused by the Mn impurity in the quantum spin chains in CuGeO3 may lead to the co-existence of the QC regime and the spin-Peierls dimerisation, is discussed. For the quantitative description of the temperature dependences of the line width and g-factor a model assuming the crossover from the high temperature semiclassical Nagata and Tazuke limit to the low temperature quantum case described by Oshikawa and Affleck theory is suggested.

cond-mat.str-el↗

arXiv2005

Magnetic resonance in cerium hexaboride caused by quadrupolar ordering

Experimental evidence of the magnetic resonance in the antiferro-quadrupole phase of CeB6 is reported. We have shown that below orbital ordering temperature a new magnetic contribution from localized magnetic moments (LMM) emerge and gives rise to observed resonant phenomenon. This behaviour is hardly possible to expect in dense Kondo system, where LMM should vanish al low temperatures rather than emerge. From the other hand, in the quadrupole ordering concept, where magnetism of Ce magnetic ions is solely accounted, is difficult to explain splitting of magnetisation into components having different physical nature. Therefore an adequate theory explaining magnetic properties of CeB6 including magnetic resonance and orbital ordering appears on the agenda.

cond-mat.str-el↗