arXiv subjects

H. Szymczak

Publications and source records attributed to H. Szymczak.

9 recordsLinked to original sources

arXiv2026

Influence of chemical ordering on magnetocrystalline anisotropy and magnetoelastic properties in Weyl magnetic semimetal Co2MnGa thin films

The magnetic anisotropy and magnetoelastic properties of the magnetic Weyl semimetal Co2MnGa were investigated in the Co2MnGa thin films with different chemical orderings. Their properties change, in line with the increase in the contents of the highly-ordered B2 and L21 phases. The most significant changes of both the magnetic anisotropy and the magnetoelastic properties were correlated with the appearance of the L21 ordered phase of Heusler alloy, which is also responsible for topological properties of these compounds. The magnetoelastic properties of L21 ordered Co2MnGa are discussed in comparison with the Co2FexMn1-xSi system with a similar degree of ordering, which has similar crystallographic structure but it is not Weyl semimetal. In particular, significant differences between the magnetoelastic properties of ordered Co2MnGa and Co2MnSi were found. In the case of L21-ordered Co2MnGa, the giant anisotropy of the magnetoelastic properties was observed.

cond-mat.mtrl-sci↗

arXiv2022

Quantum versus classical nature of a low-temperature magnetic phase transition in TbAl$_3$(BO$_3$)$_4$

Specific heat, $C_B$, of a TbAl$_3$(BO$_3$)$_4$ crystal was studied for 50 mK $<T<$ 300 K, with emphasis on $T<1$ K, where a phase transition was found at $T_c =0.68$ K. Nuclear, non-phonon ($C_m$), and lattice contributions to $C_B$ were separated. Lowering of $T_c$ with ncrease of magnetic field parallel to the easy magnetization axis, $B_{||}$, was found. It was established that $C_m$ and a Grüneisen ratio depend on $B_{||}$ and $T$ in a way characteristic of systems, in which a classical transition is driven by quantum fluctuations, QF, to a quantum critical point at $T=0$, by tuning a control parameter ($B_{||}$). The $B_{||} - T$ phase diagram was constructed and the dynamical critical exponent $0.82 \le z \le 0.96$ was assessed. Nature of the transition was not established explicitly. Magnetization studies point at the ferromagnetic ordering of Tb$^{3+}$ magnetic moments, however, lowering of $T_c$ with increase in $B_{||}$ is opposite to the classical behavior. Hence, a dominant role of QF was supposed.

cond-mat.str-el↗

arXiv2012

Magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders

The magnetic anisotropy of La0.7Sr0.3MnO3 nanopowders was measured as a function of temperature by the modified singular point detection technique. In this method singularities indicating the anisotropy field were determined analyzing ac susceptibility data. The observed relationship between temperature dependence of anisotropy constant and temperature dependence of magnetization was used to deduce the origin of magnetic anisotropy in the nanopowders. It was shown that magnetic anisotropy of La0.7Sr0.3MnO3 nanopowder is determined by two-ion (dipolar or pseudodipolar) and single-ion mechanisms.

cond-mat.mtrl-sci↗

arXiv2012

Formation of non-collinear magnetic states in the Fe(2-x)Mn(x)As system

Within the frameworks of the model using ab initio calculation data on d-band filling and on the shape of density of d-electron states in Fe2-xMnxAs, the mechanisms of stabilization of non-collinear magnetic ordered phases observed within the range of 1.19 <= x <= 1.365 are considered. The relation between baric peculiarities of the changes in stability of noncollinear phases and changes in the electronic structure characteristics of Fe2-xMnxAs due to lattice deformation is disclosed. It is found that stabilization of non-collinear phases and change in type of order-order phase transition with decreasing manganese is determined by competition between the electronic filling of the d-band, shape of the d-electron density of states and structural features of these phases.

cond-mat.mtrl-sci↗

arXiv2008

Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8

Inelastic neutron scattering measurements were performed on single crystal Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie sites within kagome staircase planes. This system displays a rich magnetic phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We have studied the low-lying magnetic excitations in this phase within the kagome plane. Despite the complexity of the system at higher temperatures, linear spin-wave theory describes most of the quantitative detail of the inelastic neutron measurements. Our results show two spin-wave branches, the higher energy of which displays finite spin-wave lifetimes well below Tc, and negligible magnetic exchange coupling between Co moments on the spine sites.

cond-mat.dis-nn↗

arXiv2002

ab-plane tunneling and Andreev spectroscopy of superconducting gap and pseudogap in (Bi,Pb)2Sr2Ca2Cu3O10 and Bi2Sr2CaCu2O8

We have measured the temperature dependence of gap features revealed by Andreev reflection Delta_s and by tunneling Delta in the ab-plane of optimal and slightly overdoped microcrystals of (BiPb)2Sr2Ca2Cu3O10 (Bi2223) with critical temperature Tc=110-115 K, and Bi2Sr2CaCu2O8 (Bi2212) with Tc=80-84 K. The tunneling conductance of Bi2223-Insulator-Bi2223 junction shows peaks at the 2Delta gap voltage, as well as dips and broad humps at other voltages. In Bi2223, similarly to the well known Bi2212 spectra, the energies corresponding to 2Delta, to the dip, and to the hump structure are in the ratio of 2:3:4. This confirms that the dip and hump features are generic to the high temperature superconductors, irrespective of the number of CuO2 layers or the BiO superstructure. On the other hand, in both compounds Delta(T) and Delta_s(T) dependences are completely different, and we conclude that the two entities have different nature.

cond-mat.supr-con↗

arXiv2002

Observation of Convergent Oscillations of the Flux Line Lattice as a Result of Magnetic Flux Jumping in Hard Superconductors

We have monitored new peculiarities of the dynamics of catastrophic avalanches of the magnetic flux in superconducting Nb, Nb-Ti, and YBaCuO samples: i) convergent oscillations of the magnetic flux; ii) a threshold for entering the huge flux avalanches in the shielding experiments; iii) a threshold for the exit of a residual flux in the trapping experiments. The observed phenomena are interpreted in terms of a theoretical model which takes into account the inertial properties of the vortex matter.

cond-mat.supr-con↗

arXiv2001

Heat capacity of mesoscopically disordered superconductors:implications to MgB$_{2}$

Electronic heat capacity was calculated for a mesoscopically disordered s-wave superconductor treated as a spatial ensemble of domains with a continuously varying superconducting properties. The domains are assumed to have sizes larger than the coherence length. Each domain is characterized by a certain critical temperature. The averaging over the superconducting gap distribution leads to quadratic temperature dependence of the specific heat at low temperatures, whereas its anomaly at the critical temperature is substantially smeared. The results explain well the heat capacity data for MgB$_{2}$, where a multiple-gap structure is observed.

cond-mat.supr-con↗

arXiv2001

Anomalous acoustoelectric effect in La_{0.67}Ca_{0.33}MnO_{3} films

We have studied acoustoelectric (AE) effect produced by surface acoustic waves (SAW) in a monolithic layered structure, composed of piezodielectric LiNbO_{3} substrate and La_{0.67}Ca_{0.33}MnO_{3} film. The experiments unexpectedly revealed in the longitudinal AE effect an anomalous contribution, invariant upon reversal of SAW propagation, which coexists with the ordinary (odd in wave vector) effect. The anomalous effect dominates near the metal-insulator transition, while the ordinary effect prevails at high and low temperatures. We show that the anomalous effect is caused by strong modulation of the film conductivity produced by the SAW elastic deformations.

cond-mat.str-el↗