Insider Trading at Zagreb Stock Exchange

This paper is the first paper that systematically observes and describes all publicly available data on insider trading on the Zagreb Stock Exchange during the period of June 2010 - June 2021. To accomplish this objective both parametric and non-parametric event-study tests are conducted using the data collected from 827 notifications published on the Zagreb Stock Exchange website. After filtering the notifications for overlapping events, there were 48 insiders’ purchase events and 50 insiders’ sales events. The results indicate that insiders can earn abnormal returns on share purchases based on their insider knowledge and that the information on insider purchases can bring additional information to outside investors. However, in the case of notifications of share sales by insiders, Cumulative Average Abnormal Returns (CAARs) after the event are not statistically significant and are just slightly positive, thus bringing no abnormal returns for insiders and not conveying information to the public. This suggests that the market may perceive sales having a lower informational content, as motivation for sales may be other needs, such as liquidity

Transport and dielectric properties of selected BEDT-TTF organic materials

Izvršena su mjerenja otpornosti i dielektrična spektroskopija pri niskim temperaturama na uzorcima kvazi-dvodimenzionalnih organskih vodiča koji su bazirani na organskoj molekuli bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF). Istraživanje spoja α -ET_2I_3 je provedeno kako bi se bolje razumjela feroelektrična priroda metalno-izolatorskog prijelaza na T_MI = 135K te pojava relaksacijskih modova u smjeru okomitom na vodljivu ravninu ispod tog prijelaza. Transportna mjerenja su pokazala promjenu vrijednosti energijskog procjepa na niskim temperaturama koja dosad nije razmatrana u literaturi. Također je izvedeno istraživanje svojstava nedavno sintetiziranog spoja κ-ET_2Ag_2(CN)_3 da bismo bolje razumjeli ponašanje srodnog κ -ET_2Cu_2(CN)_3 koji je istaknuti kandidat za pronalaženje osnovnog stanja kvantne spinske tekućine. U ovom radu je prezentirana prva dielektrična karakterizacija uzorka κ-ET_2Ag_2(CN)_3 koja je zabilježila pojavu većeg broja relaksacijskih modova.Resistance measurements and dielectric spectroscopy at low temperatures were performed on samples of quasi-two-dimensional organic conductors based on the organic molecule bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF). An investigation on the α – ET_2I_3 compound was conducted in order to better understand the ferroelectric nature of the metal-insulator transition at T_MI = 135K, as well as the appearance of out-of-plane relaxation modes below this transition temperature. Transport measurements have shown a change in energy gap values at low temperatures, which was not previously discussed in the literature. The properties of the newly synthesised compound κ – ET_2Ag_2(CN)_3 were also explored in order to better comprehend the behaviour of the related κ – ET_2Cu_2(CN)_3 which is a prominent candidate for finding a quantum spin liquid ground state. In this work the first dielectric characterization of a sample of κ – ET_2Ag_2(CN)_3 is presented which recorded an occurrence of multiple relaxation modes

Magnetotransportna svojstva odabranih visokoentropijskih slitina

This thesis presents the findings of a comprehensive, systematic study of transport properties, including resistivity, Hall effect, magnetoresistance, and superconductivity, in amorphous quinary alloys of early and late transition metals. The research focused on metallic glass ribbons from three alloy systems: (TiZrNbNi)1−xCux, (TiZrNbCu)1−xNix, and (TiZrNbCu)1−xCox, spanning a broad composition range, along with three alloy variants with a fixed TL (Cu, Ni) content and compositions: Ti0.30Zr0.15Nb0.15Ni0.20Cu0.20, Ti0.15Zr0.30Nb0.15Ni0.20Cu0.20, and Ti0.15Zr0.15Nb0.30Ni0.20Cu0.20. In addition, measurements were conducted on an amorphous thin film of TiZrNbCuNi, which was deposited on a SrLaAlO4 substrate using a pulsed laser deposition (PLD) system. The results of resistivity, Hall effect, magnetoresistance, and superconductivity measurements largely agree with those reported in previous investigations on related binary and ternary amorphous alloys. However, we identified a novel model of two parallel conducting channels, composed of a metal-like and a variable range hopping (VRH)-like channel, that better describes the temperature variation of resistivity observed in our experiments. A possible mechanism for the origin of these two conductance channels was proposed.Materijali s kristalnim uređenjem uvijek su privlačili veliki interes znanstvene zajednice, posebno od razvoja kvantne mehanike. Međutim, savršene kristalne strukture su češće iznimka nego pravilo u prirodi. Umjesto toga, strukture u materijalima variraju od kristalnih rešetci s malim brojem defekata, do vrlo neuređenih amorfnih (staklastih) struktura. Amorfni metali su čisti metali ili legure koje ne posjeduju dugodosežno atomsko uređenje, a nastaju raznim tehnikama brzog hlađenja taljevine ili plina. Brzina procesa sprječava stvaranje uređene kristalne faze pa atomi ostaju „smrznuti” u metastabilnom stanju koje nalikuje tekućoj fazi. Razvoj tehnika brzog hlađenja tijekom 1960-ih doveo je do povećanog interesa za amorfna metalna stakla i utjecaja dugodosežnog (ne)uređenja na elektronsku strukturu, mehanička, magnetska i električna svojstva metala. Među metalnim staklima, od posebnog su značaja slitine ranih (Ti, Zr, Nb, Hf) i kasnih (Fe, Co, Ni, Cu) prijelaznih metala, poznate skraćeno kao TE–TL slitine. Ove slitine su od posebnog interesa zbog širokog raspona koncentracija (obično između 20% i 70% sadržaja kasnih prijelaznih metala) za koje je moguće formirati metalno staklo. Ovo svojstvo omogućuje detaljno i sustavno proučavanje ovisnosti svojstava materijala o kemijskom sastavu, jer je kod amorfnih slitina, za razliku od kristalnih, moguće dobiti homogenu jednofaznu smjesu s kontinuiranim vrijednostima kemijskog sastava

Magnetotransportna svojstva odabranih visokoentropijskih slitina

This thesis presents the findings of a comprehensive, systematic study of transport properties, including resistivity, Hall effect, magnetoresistance, and superconductivity, in amorphous quinary alloys of early and late transition metals. The research focused on metallic glass ribbons from three alloy systems: (TiZrNbNi)1−xCux, (TiZrNbCu)1−xNix, and (TiZrNbCu)1−xCox, spanning a broad composition range, along with three alloy variants with a fixed TL (Cu, Ni) content and compositions: Ti0.30Zr0.15Nb0.15Ni0.20Cu0.20, Ti0.15Zr0.30Nb0.15Ni0.20Cu0.20, and Ti0.15Zr0.15Nb0.30Ni0.20Cu0.20. In addition, measurements were conducted on an amorphous thin film of TiZrNbCuNi, which was deposited on a SrLaAlO4 substrate using a pulsed laser deposition (PLD) system. The results of resistivity, Hall effect, magnetoresistance, and superconductivity measurements largely agree with those reported in previous investigations on related binary and ternary amorphous alloys. However, we identified a novel model of two parallel conducting channels, composed of a metal-like and a variable range hopping (VRH)-like channel, that better describes the temperature variation of resistivity observed in our experiments. A possible mechanism for the origin of these two conductance channels was proposed.Materijali s kristalnim uređenjem uvijek su privlačili veliki interes znanstvene zajednice, posebno od razvoja kvantne mehanike. Međutim, savršene kristalne strukture su češće iznimka nego pravilo u prirodi. Umjesto toga, strukture u materijalima variraju od kristalnih rešetci s malim brojem defekata, do vrlo neuređenih amorfnih (staklastih) struktura. Amorfni metali su čisti metali ili legure koje ne posjeduju dugodosežno atomsko uređenje, a nastaju raznim tehnikama brzog hlađenja taljevine ili plina. Brzina procesa sprječava stvaranje uređene kristalne faze pa atomi ostaju „smrznuti” u metastabilnom stanju koje nalikuje tekućoj fazi. Razvoj tehnika brzog hlađenja tijekom 1960-ih doveo je do povećanog interesa za amorfna metalna stakla i utjecaja dugodosežnog (ne)uređenja na elektronsku strukturu, mehanička, magnetska i električna svojstva metala. Među metalnim staklima, od posebnog su značaja slitine ranih (Ti, Zr, Nb, Hf) i kasnih (Fe, Co, Ni, Cu) prijelaznih metala, poznate skraćeno kao TE–TL slitine. Ove slitine su od posebnog interesa zbog širokog raspona koncentracija (obično između 20% i 70% sadržaja kasnih prijelaznih metala) za koje je moguće formirati metalno staklo. Ovo svojstvo omogućuje detaljno i sustavno proučavanje ovisnosti svojstava materijala o kemijskom sastavu, jer je kod amorfnih slitina, za razliku od kristalnih, moguće dobiti homogenu jednofaznu smjesu s kontinuiranim vrijednostima kemijskog sastava

Magnetotransportna svojstva odabranih visokoentropijskih slitina

This thesis presents the findings of a comprehensive, systematic study of transport properties, including resistivity, Hall effect, magnetoresistance, and superconductivity, in amorphous quinary alloys of early and late transition metals. The research focused on metallic glass ribbons from three alloy systems: (TiZrNbNi)1−xCux, (TiZrNbCu)1−xNix, and (TiZrNbCu)1−xCox, spanning a broad composition range, along with three alloy variants with a fixed TL (Cu, Ni) content and compositions: Ti0.30Zr0.15Nb0.15Ni0.20Cu0.20, Ti0.15Zr0.30Nb0.15Ni0.20Cu0.20, and Ti0.15Zr0.15Nb0.30Ni0.20Cu0.20. In addition, measurements were conducted on an amorphous thin film of TiZrNbCuNi, which was deposited on a SrLaAlO4 substrate using a pulsed laser deposition (PLD) system. The results of resistivity, Hall effect, magnetoresistance, and superconductivity measurements largely agree with those reported in previous investigations on related binary and ternary amorphous alloys. However, we identified a novel model of two parallel conducting channels, composed of a metal-like and a variable range hopping (VRH)-like channel, that better describes the temperature variation of resistivity observed in our experiments. A possible mechanism for the origin of these two conductance channels was proposed.Materijali s kristalnim uređenjem uvijek su privlačili veliki interes znanstvene zajednice, posebno od razvoja kvantne mehanike. Međutim, savršene kristalne strukture su češće iznimka nego pravilo u prirodi. Umjesto toga, strukture u materijalima variraju od kristalnih rešetci s malim brojem defekata, do vrlo neuređenih amorfnih (staklastih) struktura. Amorfni metali su čisti metali ili legure koje ne posjeduju dugodosežno atomsko uređenje, a nastaju raznim tehnikama brzog hlađenja taljevine ili plina. Brzina procesa sprječava stvaranje uređene kristalne faze pa atomi ostaju „smrznuti” u metastabilnom stanju koje nalikuje tekućoj fazi. Razvoj tehnika brzog hlađenja tijekom 1960-ih doveo je do povećanog interesa za amorfna metalna stakla i utjecaja dugodosežnog (ne)uređenja na elektronsku strukturu, mehanička, magnetska i električna svojstva metala. Među metalnim staklima, od posebnog su značaja slitine ranih (Ti, Zr, Nb, Hf) i kasnih (Fe, Co, Ni, Cu) prijelaznih metala, poznate skraćeno kao TE–TL slitine. Ove slitine su od posebnog interesa zbog širokog raspona koncentracija (obično između 20% i 70% sadržaja kasnih prijelaznih metala) za koje je moguće formirati metalno staklo. Ovo svojstvo omogućuje detaljno i sustavno proučavanje ovisnosti svojstava materijala o kemijskom sastavu, jer je kod amorfnih slitina, za razliku od kristalnih, moguće dobiti homogenu jednofaznu smjesu s kontinuiranim vrijednostima kemijskog sastava

(Magneto)Transport Properties of (TiZrNbNi)_1−<i>x</i>Cu_<i>x</i> and (TiZrNbCu)_1−<i>x</i>Co_<i>x</i> Complex Amorphous Alloys

We present a systematic study of electrical resistivity, superconductive transitions and the Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals: (TiZrNbNi)1−xCux and (TiZrNbCu)1−xCox in a broad composition range of 0x0.5 as well as Ti0.30Zr0.15Nb0.15Cu0.2Ni0.2, Ti0.15Zr0.30Nb0.15Cu0.2Ni0.2 and Ti0.15Zr0.15Nb0.30Cu0.2Ni0.2. All samples showed high resistivity at room temperature, 140–240 μΩ cm, and the superconducting transition temperatures decreased with increasing late transition metal content, similar to binary amorphous and crystalline high-entropy TE-TL alloys. The Hall coefficient RH was temperature-independent and positive for all samples (except for (TiZrNbCu)0.57Co0.43), in good agreement with binary TE-TL alloys. Finally, for the temperature dependence of resistivity, as far as the authors are aware, we present a new model with two conduction channels, one of them being variable range hopping, such as the parallel conduction mode in the temperature range 20–200 K, with the exponent p=1/2. We examine this in the context of variable range hopping in granular metals

Spin-Reorientation-Driven Linear Magnetoelectric Effect in Topological Antiferromagnet Cu3TeO6

International audienceThe search for new materials for energy-efficient electronic devices has gained unprecedented importance. Among the various classes of magnetic materials driving this search are antiferromagnets, magnetoelectrics, and systems with topological spin excitations. Cu3TeO6 is a material that belongs to all three of these classes. Combining static electric polarization and magnetic torque measurements with phenomenological simulations we demonstrate that magnetic-field-induced spin reorientation needs to be taken into account to understand the linear magnetoelectric effect in Cu3TeO6. Our calculations reveal that the magnetic field pushes the system from the nonpolar ground state to the polar magnetic structures. However, nonpolar structures only weakly differing from the obtained polar ones exist due to the weak effect that the field-induced breaking of some symmetries has on the calculated structures. Among those symmetries is the PT (¯1′) symmetry, preserved for Dirac points found in Cu3TeO6. Our findings establish Cu3TeO6 as a promising playground to study the interplay of spintronics-related phenomena

Semimetallic and charge-ordered α-(BEDT-TTF)2I3: On the role of disorder in dc transport and dielectric properties

α-(BEDT-TTF)2I3 is a prominent example of charge ordering among organic conductors. In this work, we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way to create an almost temperature-independent conductivity as well as a low Hall effect. We explain these phenomena as a consequence of a predominantly interpocket scattering which equalizes mobilities of the two types of charge carriers. At low temperatures, within the insulating charge-ordered phase two channels of conduction can be discerned: a temperature-dependent activation, which follows the mean-field behavior, and a nearest-neighbor-hopping contribution. Together with negative magnetoresistance, the latter relies on the presence of disorder. The charge-ordered phase also features a prominent dielectric peak which bears a similarity to relaxor ferroelectrics. Its dispersion is determined by free-electron screening and pushed by disorder well below the transition temperature. The source of this disorder can be found in the anion layers which randomly perturb BEDT-TTF molecules through hydrogen bonds

Hall effect study of the κ -(ET) 2X family : Evidence for Mott-Anderson localization

We investigate the dc resistivity and Hall effect of the quasi-two-dimensional organic materials κ–(ET)2X, where X=Ag2(CN)3 and B(CN)4 and compare them with the results for X=Cu2(CN)3. All three compounds are considered to be quantum-spin-disordered Mott insulators. Despite high similarities in chemical composition and crystal structure, large differences in the dc resistivity and Hall coefficient are found. While around room temperature the dc transport properties are dominantly determined by the strength of the electron correlations, upon reducing the temperature, dc transport happens by hopping due to inherent disorder. The most disordered compound with X=Cu2(CN)3 turns out to have the lowest dc resistivity and the highest charge carrier density, i.e., in the phase diagram it is located closest to the metal-insulator transition. The least disordered compound with X=B(CN)4 shows the highest resistivity and the lowest carrier density, i.e., lies farthest from the metal-insulator transition. We explain such counterintuitive behavior within the theory of Mott-Anderson localization as a consequence of disorder-induced localized states within the correlation gap