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We report on linear magnetoelectric effect observed by the static electric polarization measurements in external magnetic field up to 12 T on topological multidomain antiferromagnet Cu$_3$TeO$_6$. The polarization is non-zero only below the N\'{e}el temperature and for $\mathbf{E}\perp \mathbf{H}$. The magnetization data show spin reorientation taking place already in $H, Comment: 6 pages, 4 figures

The family of antiferromagnets (AFM) with multidomain structure is of particular importance in the fundamental research of multiferroics because they represent an opportunity to examine the dynamics of domains and domain walls, their motion, creation, or destruction, as well to examine the role of magnetoelectric (ME) effect. Here the ME effect is investigated in copper tellurium oxide, Cu3TeO6, with cubic unit cell and 3D AFM order in which copper ions form hexagons with shared vertices. Below TN = 61 K multiple domains develop with easy axes pointing along diagonals of the unit cell, resulting in 8 (4x2) AFM domains.We present ME properties of Cu3TeO6by the results of static electric polarization measurements in an external magnetic field up to 16 T for a few different orientations of electric polarization P and magnetic field H. Below TN P-E hysteresis opens (Fig. 2) by the magnetic field applied in perpendicular direction to the electric field, with saturation polarization increasing linearly with the magnetic field and behaving BCS- like with temperature. Since the symmetry analysis shows that the observed ME effect is not in agreement with the symmetry-determined ME tensor we consider two possible explanations: i) the actual symmetry of the ordered state is different than expected from neutron diffraction experiment, ii) spin reorientation within domains takes place. We analyze both and investigate possibility of ferrotoroidal order. Analysis of magnetic symmetry by studying magnetic anisotropy will be shown.

To investigate ME properties in Cu3TeO6 we performed static electric polarization measurements, dynamic dielectric spectroscopy studies and magnetic measurements in an external magnetic field up to 16 T for a few different directions of electric polarization and magnetic field. The polarization increases as the magnetic field increases when the electric and magnetic field are mutually perpendicular (at least up to 12.8 T), but the observed ME effect is not in agreement with the symmetry-determined ME tensor. There are two possible explanations for that observation. The actual symmetry of the ordered state is different than what is proposed in neutron diffraction experiment, or spin reorientation within each domain takes place. We analyze both of these possibilities and look into possible presence of ferrotoroidal order in investigated material. However, additional experimental and theoretical studies are still needed to further understand the origin of linear ME coupling and the role of quantum effects in this material.

Hexaferrites are a class of iron compounds which crystalize in a sandwich-like periodic stacking of iron-oxide layers containing different metal atoms. The simplest is the M-type with chemical formula AB12O19, where A = Ba, Pb ... and B = Fe, Ti ... Our recent measurements with frequency-dependent magnetic susceptibility technique on various substitutions within the M-type hexaferrite (Ba1−xPbxFe12−yAlyO19) has shown signatures of exotic phenomena which point toward a general relaxational mechanism in ferrimagnetic semiconductors. Moreover, it was shown that activation energies of relaxation dynamics increase by adding aluminum. Heat capacity measurements from room temperature down to liquid helium indicate that the whole temperature range can be fitted well by the Debye and Einstein contributions up to room temperature. The energy of the lowest Einstein mode came close to the energy of the Debye mode.

The family of antiferromagnets with multidomain structure is of particular importance in the fundamental research of multiferroics because they represent an opportunity to examine the dynamics of domains and domain walls, their motion, creation, or destruction, as well to examine the role of magnetoelectric (ME) effect. Moreover, some poorly understood complex excitations like electromagnons can also exist in these materials [1, 2]. A member of mentioned family is copper tellurium oxide, Cu3TeO6, which has a cubic crystal structure with a three- dimensional magnetic lattice in which copper ions form hexagons with shared vertices [3, 4]. The long-range antiferromagnetic arrangement, which occurs below TN = 62 K, is either collinear or has a small spin canting. The high cubic symmetry of this material allows eight (4x2) antiferromagnetic domains. Considering the magnetic lattice, there are two possible explanations for the ME response. A canted antiferromagnetic arrangement could yield toroidal domains each of which, with the application of a magnetic field, would have electric polarization in different directions. On the other hand, a collinear antiferromagnetic arrangement would break the symmetries of the inversion of both space and time which could explain the ME response.We present ME properties of Cu3TeO6by the results of static electric polarization measurements in an external magnetic field up to 16 T for a few different orientations of electric polarization P and magnetic field H. Below TN P-E hysteresis opens (Fig. 2) by the magnetic field applied in perpendicular direction to the electric field, with saturation polarization increasing linearly with the magnetic field and behaving BCS-like with temperature. Since the symmetry analysis shows that the observed ME effect is not in agreement with the symmetry-determined ME tensor [5] we consider two possible explanations: i) the actual symmetry of the ordered state is different than expected from neutron diffraction experiment [4], ii) spin reorientation within domains takes place. We analyze both and investigate possibility of ferrotoroidal order. Analysis of magnetic symmetry by studying magnetic anisotropy will be shown.

Hexaferrites are a class of iron compounds which crystalize in a sandwich-like periodic stacking of iron-oxide layers containing different metal atoms. The simplest is the M-type with chemical formula AB12O19, where A = Ba, Pb ... and B = Fe, Ti ... [1] Our recent research [2, 4] on various substitutions within the M-type hexaferrite has shown signatures of exotic phenomena which point toward a general relaxational mechanism in ferrimagnetic semiconductors. Frequency - dependent magnetic susceptibility (Fig. 1) and dc electric transport properties of three different compositions of hexaferrite Ba1−xPbxFe12−yAlyO19 show a correlation between activation energies which persists in the whole researched range of aluminum substitution x = 0 to 3.3. This result is discussed in the context of charged magnetic domain walls, the pinning of which is determined by charge carriers activated over the transport gap.

The one-dimensional (1D) electronic systems are a fascinating subject of scientific c research because when con ned to one dimension, itinerant electrons undergo transitions to different types of collective ground states. A common example of such transition is Pierls transition from a high- temperature metallic state to a low-temperature charge density wave (CDW) semiconducting state, due to strong electron-phonon coupling. Halogenated transition metal tetrachalcogenides of the (MX4)nY family (M = Nb ; Ta ; X = S ; Se ; Y = I ; Br) provide a typical example of 1D compounds that can potentially undergo CDW transition and exhibit nonlinear transport properties. To explore those properties we can employ a range of di erent experimental techniques. Among them, dielectric spectroscopy is an appropriate technique for investigation of dynamics of the phase degree freedom in CDW systems. However, to have a complete understanding of the dynamical properties of the material it is important to obtain the information from several complementary experiments. In this seminar, I will present transport and spectroscopic (pump-probe and dielectric) studies on the halogenated niobium tetraselenide, (NbSe4)3I. It is the only representative of 1D halogenated transition metal tetrachalcogenides which does not undergo typical Pierls transition into the CDW ground state. Instead, a structural ferrodisortive transition without a noticeable appearance of the superstructure has been observed. In addition to the properties of the equilibrium state, I will also present some unpublished results of photoinduced metastable states in this compound.

Tracking crystal vibrations following an excitation provides information about electron system, optic phonons (crystal vibrations) and their mutual coupling inside a crystal. Both excitation and the tracking-probes are provided by or derived from ultrashort laser pulses, i.e. with duration in sub-picosecond, or even sub-femtosecond, time scales. Weak excitation of a system is useful to study the ground state, thermal equilibrium properties. On the other hand cranking up the excitation energy can lead to another state, even one hidden from the thermal equilibrium. Here I will present such responses in few cases of correlated systems, bearing strong coupling between electrons and phonons.

M-type barium hexaferrites from the (Ba, Pb)Fe12O 19 family show a dramatic influence of lead-doping on dielectric, magnetic, as well as optical properties. The parent compound BaFe 12 O 19 is a well-known semiconducting ferrimagnet with broad range of application. On the other hand, the PbFe 12 O 19 material shows both ferromagnetic and ferroelectric properties above the room temperature. Spin and charge of iron ions within the structure of this system suggest there might a coupling between magnetic and dielectric excitations. We report on our investigation of dynamic magnetic and dielectric properties on single- crystalline lead-substituted hexaferrite (Ba, Pb)Fe 12 O 19 . On the basis of ac magnetic susceptibility and dielectric spectroscopy in radio-frequency range and low temperatures we show that the presence of lead in (Ba, Pb)Fe 12 O 19 , as compared to pristine BaFe 12 O 19 , leads to emergence of pronounced relaxations both in dielectric and magnetic sector. Their characteristic relaxation times and activation energies are similar which suggests a bi- relaxor nature of the chosen composition of (Ba, Pb)Fe 12 O 19 . We discuss the dispersion of these relaxations and their origin in the context of magnetic domains walls and the influence of doping on the crystal lattice dynamics of the M-type barium hexaferrite. This work was supported by the Russian Ministry of Education and Science Project 5-100 and Croatian Science Foundation projects IP-2013-11-1011 and IP-2018-01-2730. References: rd [1] L. Alyabyeva et al., Proceedings of the 43 International Conference on Infrared Millimeter and Terahertz Waves (IRMMW-THZ) (2018) [2] S. E. Rowley et al., Scientific Reports 6, 25724 (2016). [3] S. E. Rowley et al., Phys. Rev. B 96, 020407(R) (2017). [4] E. S. Zhukova et al., Solid State Sciences 62, 13 (2016). [5] G. L. Tan and W. Li, J. Am. Ceram. Soc. 98, 1812 (2015).

We have studied low temperature specific heat (LTSH) in different glass-forming metallic alloys: binary marginal glasses ZrNi [1], bulk metallic glasses CuHfTi [2] and high entropy metallic glasses TiZrNbCuNi(Co) [3]. The results concerning so-called boson peak (BP) contribution to the density of vibrational states in excess to the Debye contribution are quite varied between these alloys. While Zr77Ni23 does not show BP, in Cu55Hf45- xTix its position and amplitude vary monotonously with the Ti content, Fig. 1. In TiZrNbCuNi(Co) alloys with multiple principle elements, the position of BP scales roughly with the Debye temperature, while its amplitude shows more complex behaviour. We discuss these results in respect of the intrinsic differences between these alloys [4] and in the view of different theories of BP, see e.g. [5, 6]. [1] A. Salčinović Fetić et al., Phys. Rev. B 96 (2017) 064201. [2] G. Remenyi et al., Appl. Phys. Lett. 104 (2014) 171906. [3] E. Babić et al., J. Mater. Res. 33 (2018) 3170. [4] W. H. wang, JOM 66 (2014) 2076. [5] T. Brink et al., Phys. Rev. B 94 (2016) 224203. [6] M. Baggioli and A. Zaccone, Phys. Rev. B 122 (2019) 145501.

Single crystalline lead-substituted barium hexaferrite compounds are studied in a broad spectral range, 10^2 Hz to 2*10^14 Hz. We observe excitations of different nature including dielectric and magnetic relaxations coexisting within the same frequency and temperature ranges and electronic transitions between the fine-structure components of the split Fe2+ ground state level.

We observe the excitation of collective modes in the terahertz (THz) range driven by the recently discovered N´eel spin-orbit torques (NSOTs) in the metallic antiferromagnet Mn2Au. Temperaturedependent THz spectroscopy reveals a strong absorption mode centered near 1 THz, which upon heating from 4 to 450 K softens and loses intensity. A comparison with the estimated eigenmode frequencies implies that the observed mode is an in-plane antiferromagnetic resonance (AFMR). The AFMRabsorption strength exceeds those found in antiferromagnetic insulators, driven by the magnetic field of the THz radiation, by 3 orders of magnitude. Based on this and the agreement with our theory modeling, we infer that the driving mechanism for the observed mode is the current-induced NSOT. Here the electric field component of the THz pulse drives an ac current in the metal, which subsequently drives the AFMR. This electric manipulation of the N´eel order parameter at high frequencies makes Mn2Au a prime candidate for antiferromagnetic ultrafast memory applications.

In the last decade, we have produced several series of thin films of charge density wave (CDW) system K0.3MoO3 by pulsed laser deposition [1-4]. Films have granular structure with typically sub- micron grain size, resulting in somewhat suppressed CDW transition and electric conductivity governed by the variable range hopping mechanism. Recently, for the first time, we have obtained an order of magnitude longer (2-4 m) and well patterned grains, as shown by AFM images in the Figure 1. Electrical conductivity and femtosecond pump- probe response in these films exhibit significant similarity with bulk samples, while the grain length is comparable to the CDW coherence length.

International audience; We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor (NbSe 4) 3 I by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a welldocumented pseudo-Jahn-Teller ferrodistortive structural transition at T C = 274 K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at T * ≈ 160 K. Although antiferroelectric (AFE) phase is partially formed at T C , our results consistently point to an enhancement of the interchain order at T * , thus leading to AFE order-disorder transition, as supported by the earlier dielectric and structural studies.

Electric conductivity of charge density wave (CDW) systems exhibits rich variety of behavior ; thermal activation across the gap at low fields below transition temperature TP, collective contribution (nonlinear conductivity channel) above the threshold field (ET) and variable range hopping (VRH) at low temperatures and in granulated thin films in the whole temperature range . Particularly the origin of the hopping conductivity is still unclear. We have investigated the influence of disorder on conductivity phenomena in CDW systems TaS3 and blue bronze (BB: K0.3MoO3) in a wide range of temperatures and electric fields using both the DC and pulse measurements at low and high fields respectively. Disorder has been introduced in several ways: (1) synthesis of TaS3 samples doped with Nb, (2) irradiation of nominally pure TaS3 samples and (3) deposition of granular thin BB films by pulsed laser deposition (PLD). Our results show that the nonlinear conductivity can be described by VRH already below 50 K in contrast to the linear channe, where it appears only below 20 K. Moreover, the point defects in TaS3 introduced by doping and irradiation have no effect on VRH. Together with the dielectric data, it suggests the microscopic picture of soliton hopping in CDW at low temperatures. In granular thin BB films, on the other hand, the influence of grain boundaries is overwhelming even above TP, which is in contrast to the previous experiments on thin BB films. The results can be understood by applying recent theoretical results for Beloborodov's Efros- Shlovskii VRH in granular materials.

Quasi‐one‐dimensional metal (q‐1D) K0.3MoO3, exhibits so‐called Peierls transition to a charge density wave (CDW) state with periodic charge density modulation and concomitant lattice distortion at a transition temperature Tp=180 K. Despite the fact that the physical properties of q‐1d bulk materials have been widely investigated, they can drastically change due to reduced dimensionality if the material is in the form of thin film. We present results of the production of K0.3MoO3 thin films by pulsed laser deposition (PLD). Standard characterization techniques showed that our films are composed of nano‐sized metallic grains and presence of CDW in grains was unambiguously proved by femto‐second time resolved spectroscopy (fs‐Trs). This technique also showed that the amplitude mode appears in films at a temperature that is some 30 K lower than in the crystal. Transport measurements in a wide temperature range indicated smeared Peierls transition in some films, at a temperature that is some 30 K lower than in bulk, which is in accordance with fs‐Trs. We have established a connection between film morphology and resistance, namely films with better ordering show lower resistance and more pronounced anomaly at 150 K. Furthermore, our films appear to be well fit by variable range hopping conductivity (VRH) in the almost entire temperature range, which is a characteristic of disordered materials.

U ovom radu je predstavljen utjecaj parametara proizvodnje (temperatura podloge Ts i parcijalni pritisak oksigena p02) na granularne tanke filmove K0.3MoO3 (kalijeva plava bronza) proizvedene pulsnom laserskom depozicijom (PLD). Filmovi su ispitani različitim standardnim tehnikama kao što su UV-vis spektroskopija, skenirajuća elektronska mikroskopija (SEM), rendgenska difrakcija (XRD), mikroskopija atomskim silama (AFM), femtosekundna- vremenski razlučiva spektroskopija (fs-TRs) i mjerenje električnog transporta. Općenito, K0.3MoO3 predstavlja prototip kvazi- jednodimenzionalnog (q-1D) materijala koji prelazi u kolektivno stanje vala gustoće naboja (VGN) na temperaturama nižim od temperature prelaza Tp. Njegova svojstva su dobro poznata i ispitana u kristalima, a zbog smanjene dimenzionalnosti, filmovi sa VGN stanjem omogućavaju proučavanje fizikalnih svojstava ovih sistema na mezo i mikro skalama. Amaliza eksperimentalnih rezultata pokazuje da su filmovi sastavljeni od nanokristalnih zrna čija veličina i orjentacija zavise od parametara proizvodnje. Mjerenja električnog transporta i fs- TRs su omogućila detekciju faznog prelaza u VGN osnovno stanje na temperaturi oko 30 K nižoj u filmu nego u kristalu.

U ovoj disertaciji izučavan je utjecaj defekata na prijelaz u stanje vala gustoće naboja (VGN) i svojstva niskoenergetskih pobuđenja faze VGN-a, u ozračenim i dopiranim uzorcima VGN sistema o-TaS3. Smrzavanje fazne dinamike na temperaturi TG, kao dio složenih svojstva niskoenergetskih pobuđenja u VGN sistemima, posljedica je vezanja VGN-a sa defektima i slobodnim nosiocima naboja. Predloženi kriterij smrzavanja1, prema kojem je TG određena brojem slobodnih nosilaca naboja u domeni korelacije faze VGN-a je, kao glavni motiv istraživanja, u ovoj disertaciji potvrđen na uzorcima sa širokim rasponom udjela defekata. Transportna i dielektrična mjerenja, u širokom temperaturnom, naponskom i frekventnom području, pokazuju da defekti uzrokuju promjenu polja praga, niskofrekventne dinamike i dielektrične konstante, ali ne i linearne vodljivosti iznad TG, dok je ispod TG opažena samo promjena u linearnoj vodljivosti. Pokazano je da je zapinjanje faze u ozračenim uzorcima iznad TG jakog, a u dopiranim slabog karaktera. Ispod TG javlja se nelinearni kanal vodljivosti skokova varijabilnog dosega. In this dissertation the influence of defects on the transition to charge density wave (CDW) state and properties of low energy CDW phase excitations has been studied in irradiated and doped samples of CDW system o-TaS3. Phase dynamics freezing at a temperature TG, as a part of complex properties of low energy excitations in CDW systems, is a consequence of CDW coupling to defects and free charge carriers. As the main motive of this research, proposed freezing criterion1 (according to which TG is determined by a number of free charge carriers within a CDW phase correlation domain) has been confirmed in samples with a wide range of defects. Transport and dielectric measurements, over a wide temperature, voltage and frequency range, show that the defects influence the threshold field, low-frequency dynamics and dielectric constant, but not the linear conductivity above TG, while below TG only an influence on the linear conductivity has been observed. Strong and weak phase pinning mechanisms above TG are confirmed in irradiated and doped samples, respectively. Below TG variable range hopping type of nonlinear conductivity channel appears.

The first thin-film growth of the “blue bronze”, oxide X0.3MoO3, well-known for its charge density wave (CDW) ground state, with X=Rb was realized a decade ago by pulsed laser deposition (PLD). However, the deposition of X=K blue bronze thin films was successfully realized only last year. The relevant parameters for successful PLD are the repetition rate, the fluence, the number of pulses, the distance between the target and the substrates, the substrate temperature and the oxygen pressure. Keeping all other parameters constant, we have varied the oxygen pressure between 0.01 mbar and 0.1 mbar and the substrate temperature between 375 °C and 450 °C with several attempts at 350 °C and 500 °C. Here we present the optimal conditions in p-T parameter space for the pulsed laser deposition of K0.3MoO3 films based on the characterization by several standard methods.

We present the temperature and magnetic field dependence of the heat capacity Cp of quasi one-dimensional system CuSeO3 and quasi two-dimensional system Fe8Te12O32Cl6. CuSeO3 [1] has an orthorhombic structure with linear Cu2+ chains very similar to CuGeO3 [2], a well known spinPeierls system [3]. We have observed a BCS-like transition at Tc=8.2 K with very similar features as in CuGeO3 [4], including the broad maximum in the magnetic contribution to Cp well above Tc [5]. However, the transition did not change even in the magnetic field of 8 T whereas in CuGeO3 both Tc and DCp at Tc decrease by 10% for in the same field [6]. Moreover, the magnetic susceptibility of CuSeO3 indicates AFM ordering and magnetic anisotropy even more complex diagram with probable tetramerization of Cu2+ spins along the chain. Fe8Te12O32Cl6 is a quasi two-dimensional system with the magnetically active Fe atoms arranged on the distorted honeycomb lattice within the layer [7]. Although Fe8Te12O32Cl6 is a good insulator, the low temperature Cp shows a strong linear contribution. However, this linear contribution ceases at the transition temperature Tc=30 K. The transition is rather small and wide, and the overall entropy change is only 3 J/mole K. Tc corresponds nicely with the narrow maximum in the magnetic susceptibility which does not resemble any standard transition. Both Tc and DCp at Tc decrease strongly with applied magnetic field and at 0.5 T it is hardly observable in the background of the lattice contribution. Magnetic susceptibility is similarly strongly dependent on applied magnetic field below 30 K, however at lower temperatures shows clearly the spin-flop transition characteristic for AFM order. We assign tentatively the results of Cp to the strongly fluctuating one-dimensional AFM order which sets in at 30 K and supports spin wave excitations below Tc. [1] K. Kohn et al., J. Solid State Chem. 18 (1976) 27 [2] H. Völlenkle et al., Monatsch. Chem. 98 (1967) 1352 [3] K. Uchinokura, J. Phys.: Condens. Matter 14 (2002) R195 [4] S. Sahling et al., Solid State Commun, 92 (1994) 423 [5] M. Weiden Z. Phys. B 98 (1995) 167 [6] G. Remenyi et al., J. Low Temp. Phys. 107 (1997) 243 [7] R. Becker, M. Johnsson, J. Solid State Chem. 180 (2007) 1750

Probing charge density wave system (CDW) o-TaS3 with dielectric spectroscopy reveals two processes determined by the CDW phase dynamics, one of which (-process) freezes at finite glass transition temperature TG at which there is less then one free carrier per phase coherence domain [1]. Irradiating the samples by 2 MeV protons we introduced interstitials and vacancies in the lattice, uniformly throughout the sample. We have observed gradual decrease of amplitude of the -process upon increasing the radiation dose, along with an increase of TG, while the other (-process) has been left unchanged. Increase of TG depends on the irradiation dose, and consequently on the domain size, in the activated manner (see Figure). It follows closely the temperature dependence of free carrier density, which does not change with the irradiation. Our results confirm previously suggested freezing criterion for CDW phase [1]. [1] D. Starešinić et. al. Phys. Rev. B 65 (2002) 165109.

Thin granular films of charge density wave (CDW) system K0.3MoO3 were prepared by pulsed laser deposition and investigated by various standard characterization methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV-vis spectroscopy. While all these methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive femtosecond time-resolved spectroscopy (fsTRS) that demonstrates the charge density wave nature of the ground state and therefore proves directly the presence of K0.3MoO3. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films in respect to single crystals, which is attributed to the granularity and crystal growth morphology. Our results establish fsTRS technique as the indispensible tool for the detection and characterization of complex ground states in nano-sized systems. Photoinduced reflectivity transients in a) bulk K0.3MoO3 and b) thin film of K0.3MoO3 on Al2O3 substrate as a function of temperature recorded at the same excitation density.

Požari otvorenog prostora su predstavnici prirodnih katastrofa s veoma ozbiljnim ekološkim, društvenim, zdravstvenim i ekonomskim posljedicama te kao primjer iznimno kompleksne pojave zahtijevaju rigorozni znanstveni pristup. Prikazat ćemo analizu više od 45 000 požara otvorenog prostora zabilježenih u periodu od 1996. do 2007. godine na teritoriju Republike Hrvatske. Statistički zakoni koje slijede raspodjele opožarenih površina ili dinamiku izbijanja požara imaju univerzalne oblike i njihovi parametri se mogu dovesti u korelaciju s naseljenošću, tradicijom, klimatskim karakteristikama, vegetacijom, kao i osnovnim karakteristikama lokalne protupožarne zaštite (npr. broja vatrogasaca, dužine prosjeka...). Takve statističke analize mogu pomoći u određivanju vjerojatnosti događanja novih požara određenih karakteristika, kao i modeliranju mogućih razvoja požara na određenoj lokaciji. Sve to ukazuje na važnost formiranja kvalitetnih baza podataka sa svim relevantnim podacima i njenog strukturiranja prema vrsti informacija ili cilja same obrade. Wildland fires are the representatives of natural disasters with serious ecological, social, health and economic consequences and as an example of an extremely complex phenomenon require a rigorous scientific approach. We will present an analysis of more than 45 000 wildland fires recorded in the period from 1996 to 2007 on the territory of the Republic of Croatia. Statistical laws describing the distribution of burned area and fire dynamics exhibit universal forms and their parameters can be correlated with the population, historical and climatic features, vegetation, and the basic characteristics of the local fire protection (e.g., number of firefighters, average length...). Such statistical analysis can help determine the probability of new events of certain characteristics, and modeling of the possible fire propagation at a particular location. All this demonstrates the importance of the formation of high-quality database with all relevant information and appropriate structuring by type of information or purpose of its treatment.

The family of glasses includes nowadays numerous systems which are often very different from the classical glassformers, i.e. supercooled liquids. Even such exotic systems as charge density wave (CDW) superstructures occurring in quasi one-dimensional metals exhibit phenomena typical for glasses [1-3] including freezing of the primary relaxation (α) process at a finite temperature Tg [1], occurrence of the secondary (β) relaxation process below Tg [1], “Boson peak”- like [2] and power-law contributions [3] to the heat capacity. Disorder in CDW glasses is introduced on the level of superstructure through the pinning of CDW to crystalline defects which break CDW in domains determined by the coherence of the complex order parameter phase. Domain interaction is controlled by the screening of residual free carriers excited over CDW gap. Increase of the relaxation time at low temperatures follows the activated increase of resistivity which plays the role of viscosity. The glass transition occurs at a temperature Tg at which there is less then one free carrier per domain and the screening is no longer effective [1]. We have varied domain sizes in CDW system o-TaS3 over two orders of magnitude by proton irradiation which created additional defects. Dielectric spectroscopy on irradiated samples shows decrease of the amplitude and the microscopic relaxation time of α process, while the activation energy increases beyond the activation energy of resistivity, demonstrating increased cooperativity of the domains. Corresponding increase of Tg depends on the irradiation dose, and consequently on the domain size, in the activated manner. It follows closely the temperature dependence of free carrier density, which does not change with the irradiation, thus corroborating the freezing criterion for CDW glass. We demonstrate that Tg is closely related to the domain size in CDW glasses. As the microscopic model of CDW dynamics is well-established, our results might contribute to the understanding of the glass phenomenology in general.

Val gustoće naboja je statička prostorna modulacija rešetke i elektronske gustoće nastala elektron-fonon interakcijom. Prva teorija koja predviđa pojavu vala gustoće naboja (VGN) potječe iz 1954 u članku H. Fröhlicha, u kojem on pokušava objasniti pojavu supravodljivosti anomalnim efektima u kvazi jednodimenzionalnim (q-1D) sustavima. Tek tri desetljeća nakon, prvi eksperimentalni rezultati su potvrdili postojanje VGN sustava. I danas su ovakvi sustavi još uvijek zanimljivi za istraživanje zbog bogatstva otkrivenih efekata. Među ostalim, u VGNu se zbog nasumičnog zapinjanja na nečistoćama javljaju metastabilna stanja koja dovode do pojave histereze u raznim fizikalnim svojstvima, od kojih je najkarakterističnija ona u temperaturnoj ovisnosti DC vodljivosti. Predstavit ću temperaturnu histerezu niskofrekventnog dielektričnog odziva i električne vodljivosti na niskim poljima, kao i histerezu nelinearne vodljivosti u električnom polju VGN sustava $o-TaS_{;3};$. Između VGN prijelaza na 220 K i staklastog prijelaza na 50 K i amplituda i vrijeme relaksacije niskofrekventnog relaksacijskog procesa su viši u grijanju nego u hlađenju sa sličnim temperaturnim ovisnostima kao i histereza otpornosti na niskim poljima. Naši rezultati sugeriraju da je histereza u dielektričnom odzivu povezana sa histerezom u DC otpornosti putem zasjenjenja VGN faze slobodnim nosiocima. U nelinearnoj vodljivosti postoji samo histereza u polju i to samo u prvom ciklusu polja, nakon dovoljne promjene u temperaturi, kada se postepenim povećanjem polja sustav dovodi kroz niz metastabilna stanja. Ovaj efekt se odnosi na unutarnje opuštanje VGN-a koje prethodi klizanju VGN-a.

We present the effects of the isoelectronic supstitution of Ta by (0.2 and 0.5 %) Nb atoms on the charge density wave (CDW) properties in o-TaS3. The characteristic, primary relaxation process which gives the maximum in the dielectric constant near 100 K disappears with slight doping. At the same time the minimum in threshold field in the same temperature range disappears as well, which is expected from well known relation between ET and low frequency dielectric constant [1]. This implies that the primary process it mainly due to polarization on order of domain scale, which decreases by doping. The secondary process, on the other hand, as well as low energy excitation contribution to specific heat (CLEE), seem to be unchanged. Only the amplitudes of the two are increased [1, 2], as both are due to the local excitations of the CDW phase in vicinity of defects described by two level system (TLS) model. [1] Staresinic et. al, Phys. Rev. B, 65, 165109 (2002) [2] Biljakovic et. al, Europhys. Lett., 62 (4), pp. 554--560 (2003)

Niz kvazi jednodimenizonalnih lančastih vodiča baziranih na TMTSF molekuli prelazi na niskim temperaturama u stanje vala gustoće spina (VGS) koje odgovara nesumjerljivom anitferomagnetskom stanju. S druge strane, snižavanjem temperature ispod VGS prijelaza dielektrični odziv pokazuje porast dielektrične konstante praćen usporavanjem niskofrekventnog procesa opuštanja koje dovodi do prijelaza u stanje VGS stakla. Takvo ponašanje karakteristično je za takozvane relaxor feroelektrike. Supostojanje magnetskog i nabojnog ured¯enja ukazuje na multiferoicˇnu prirodu VGSa i otvara moguc´nost da su magnetska i dielektricˇna svojstva med¯uovisna. Naša mjerenja niskofrekventnog dielektričnog odziva dvaju VGS sistema, (TMTSF)2AsF6 i (TMTSF)2PF6, u magnetskom polju do 8 T pokazuju jaku povezanost magnetskih i nabojnih stupnjeva slobode. Povećavanjem magnetskog polja u smjeru tvrde osi VGSa dielektrična konstanta i vrijeme opuštanja povećaju se do za red veličine, naročito u okolici temperature prijelaza u staklo od oko 2 K. Taj takozvani magnetokapacitivni efekt izraženiji je od otprije poznatog magnetootpornog efekta. Zbog toga se ne može objasniti samo promjenom zasjenjenja slobodnim nosiocima naboja, već se mora uzeti u obzir i direktan utjecaj magnetskog polja na stanje VGSa, na primjer kroz povećanje elastičnosti ("mekšanje") VGSa ili kroz smanjenje jakosti zapinjanja.

In charge density wave (CDW) systems the interaction of CDW superstructure with the random defects introduces the localized low energy states which are responsible for various glass-like phenomena. In particular, the cooperative dynamics of phase coherent domains leads to the glass transition [1] on the level of the CDW superstructure. The domain size, which depends on the amount of disorder, is supposed to play an important role in determination of the glass transition. In order to test this assumption we have investigated the dielectric response and the nonlinear conductivity of a number of o-TaS3 samples irradiated with protons in a wide range of irradiation doses. Our results demonstrate that the increase of disorder with irradiation leads to the strong decrease of the low frequency dielectric response corresponding to the high temperature relaxation process ( process of [1]), but does not affect substantially the low temperature, or  process. Moreover, the relaxation time of  process increases faster at low temperatures, indicating the increase of the glass transition temperature. At sufficiently high irradiation doses  process in not detectable any more, consistent with prior results for Nb doped samples [2]. The threshold field ET, on the other hand, increases with irradiation. This increase is non-uniform and it is the most pronounced in the temperature region where the  process dominates. This leads to the quantitative changes in the temperature dependence of ET, where a characteristic minimum disappears at high irradiation doses. Nevertheless, the inverse proportionality of ET and the dielectric constant still remains. [1] D. Starešinić, K. Biljaković, W. Brütting, K. Hosseini, P. Monceau, H. Berger, F. Levy, Phys. Rev. B 65, 165109 (2002) [2] D. Starešinić, K. Biljaković, P. Lunkenheimer, A. Loidl, J. C. Lasjaunias, J. Phys. IV France 131, 191 (2005)

Multiferroics, materials with coupled different types of order, such as electric, magnetic and structural, have raised a lot of interest recently due to the multiple application possibilities. Spin density wave (SDW) systems with their incommensurate antiferromagnetic order [1] and relaxor ferroelectric-like dielectric response [2] seem natural candidates to exhibit such phenomena, as some early results indicate [3]. We have measured the low frequency dielectric response of CDW system (TMTSF)2AsF6 at very low temperatures down to 1.9 K in the magnetic fields up to 8 T. The influence of the magnetic field on the dielectric properties is negligible with the field in the direction of the easy axis b’, while it is important with the field in the direction of the hard axis c*. This effect is the most pronounced at the lowest temperature. As expected [4], at 1.9 K the resistivity increases up to 4 times almost linearly with the field. However, both the amplitude and the relaxation time of the low frequency relaxation process [2] increase for at least an order of magnitude. As such increase cannot be explained by free carrier screening only, we conclude that the magnetic field has to influence the SDW state directly as well. In addition, our results indicate the existence of the phase transition at 2.1 K [3], and the increase of the SDW glass transition temperature [5] with the magnetic field. [1] W.M. Walsh et al., Phys. Rev. Lett. 45, 829 (1980) ; J.C. Scott et al., ibid. 45, 2125 (1980) [2] F. Nad’, P. Monceau, K. Bechgaard, Solid State Commun. 95, 655 (1995) [3] J. L. Musfeldt, M. Poirier, P. Batail, C. Lenoir, Phys. Rev. B 52, 15983 (1995) [4] P. M. Chaikin, P. Haen, E. M. Engler, R. L. Greene, Phys. Rev. B 24, 7155 (1981) [5] J. C. Lasjaunias, et al, Phys. Rev. Lett. 72, 1283 (1994)

Hrvatska je zemlja relativno bogata šumama ; 36 % od ukupne površine države pokrivaju šumske površine. Me|utim, poseban problem na jadranskom području Hrvatske predstavljaju šumski požari, koji uništavaju prirodna bogatstva smanjuju}; ; i biološku raznolikost, a negativan utjecaj imaju i na krajobraznu raznolikost. Sam problem je višeslojan, kompleksan i zahtijeva uključivanje brojnih grana znanosti, kao što su šumarstvo, geologija, biologija, meteorologija, a u zadnje vrijeme i fizika. Poznato je da fizika uspješno prepoznaje osnovna načela pojavnosti i djelovanja u materijalnom svijetu, a to ima vrlo široku primjenu i izvan njenih vlastitih okvira. Načini manifestacije komplesnosti i posebno zakonitosti koje fizičari sve više u suradnji s drugim disciplinama nalaze i proučavaju otvaraju vrlo široke horizonte mogu}; ; ih primjena. “ Korelacije u kompleksnim sustavima: od fizike do biotehnologije” je naziv interdisciplinarnog programa kojega financira Ministarstvo znanosti, obrazovanja i športa, koji je me|u inim povezao znanstvene pristupe fizike i šumarstva na proučavanju šumskih požara. Ovaj rad daje neke osnove o šumskim požarima specifične za svaku znanstvenu disciplinu i pokazuje mogu}; ; nosti njihove interakcije kao i važnost takvog interdisciplinarnog pristupa u rješavanju goru}; ; ih problema vezanih uz šumske požare i njihovu prevenciju.

We have studied the charge density wave (CDW) repolarization dynamics in blue bronze by applying square-wave voltages of different frequencies to the sample and measuring the changes in infrared transmittance, proportional to CDW strain. The frequency dependence of the electrotransmittance was fit to a modified harmonic oscillator response and the evolution of the parameters as functions of voltage, position, and temperature are discussed. Resonant frequencies decrease with distance from the current contacts, indicating that the resulting delays are intrinsic to the CDW with the strain effectively flowing from the contact. For a fixed position, the average relaxation time has a voltage dependence given by τ 0∼ V− p , with 1

We report on new method of measuring sample length, based on interferometric measurements. Motivation for exploring this technique is to study the coupling between charge density wave (CDW) and underlying crystal lattice. Several papers report the dilatation measurements on CDW systems which can be related to CDW transition [1], CDW hysteresis [2], as well as low Temperature glass transition [3]. Coupling with lattice is also evident from calorimetric measurements at glass transition temperature [4]. Our aim is to apply this method to other CDW systems as well as other systems with electronic superstructure.

In this talk, we will describe our use of IR electrotransmittance to study the dynamics of CDW repolarization in blue bronze.

We have measured the temperature dependence of the electro-transmittance of the quasi-one dimensional charge-density-wave (CDW) conductor blue bronze at temperatures between 55 K and 125 K when square-wave voltages are applied to the sample. For voltages well-above the threshold for nonlinear current, the characteristic electro-optic relaxation time, at a given position in the sample, depends primarily on the CDW current, whereas the magnitude of the relative change in transmittance decreases with decreasing temperature even for constant CDW current. At lower voltages, the frequency dependence of the response broadens, suggesting non-uniform and temperature dependent barriers to CDW repolarization.

U velikom broju sistema s valovima gustoće naboja (VGN) javlja se temperaturna histereza u električnoj vodljivosti. Za VGN sistem o-TaS3 pokazano je da se primjenom dovoljno velikog električnog polja, reda veličine kritičnog polja klizanja VGNa, električna vodljivost na zadanoj temperaturi poprima istu ravnotežnu vrijednost bez obzira na prethodni smjer promjene temperature. Analizom razlike neravnotežne i ravnotežne I/V karakteristike pokazano je kako je mehanizam opuštanja iz neravnotežnog stanja jednak mehanizmu nelinarne vodljivosti VGNa u ravnotežnom stanju. Različit iznos promjene vodljivosti tijekom opuštanja u uvjetima grijanja i hlađenja objašnjen je nesimetrijom u kritičnom odstupanju kemijskog potencijala.

Još od 19. stoljeća ljudi su pokušavali objasniti pojave u ekonomiji pomoću fizikalnih pojava. U novije vrijeme je to izraslo u posebno interdisciplinarno područje znanosti, ekonofiziku. Jedno područje interesa ekonofizike je raspodjela novca, a kao alati su se do sada koristile analize iz statističke fizike. Za analizu mi smo iskoristili podatke dobivene telefonskom anketom o primanjima kućanstava koju je proveo Državni zavod za statistiku 1998. godine. U konkretnom slučaju uočili smo dvovrsnu zakonitost razdiobe: eksponencijalnu (dominantnu na nižim vrijednostima primanja) i zakon potencije (dominantan na višim vrijednostima). Eksponencijalnu raspodjelu u fizici karakterizira parametar koji zovemo temperatura, pa nam je namjera bila uvesti i obraditi pojam "ekonomske temperature". Iz raspoloživih podataka dobili smo parametre za pojedinu raspodjelu i točku prijelaza iz jedne raspodjele u drugu interpretiranu kao prijelaz u režim "više srednje klase". Potrebno je naglasiti, da smo mi radili analizu nad novčanim dobrima, ne ukupnim, a ukupna dobra odgovaraju trenutnom bogatstvu neke obitelji.

Since 19th century scientists have been trying to correlate economy and physics. Lately it has grown into a new science field called econophysics which makes heavy use of mathematical tools taken from statistical physics. One of many problems econophysicists take interest in is distribution of money. Our data for statistical models has been taken from a telephone poll conducted in 1998 (on little more than 3000 families), containing annual income (annual wages and pensions) and number of adults per familly. We noticed that most of our data (95% of all data!) follows an exponential distribution, which can be characterized by defining corresponding temperature of economy1. Therefore we defined and calculated “ temperature of the Croatian economy” . The remaining data points, corresponding to larger incomes, follow a power-law distribution characterized by Pareto's exponential2. At last, we defined and calculated the threshold (crossover) income with which one passes into the “ higher middle class” 3 - a break-point between the two distributions. We compared our results with similar analysis for USA, Great Britain4 and Japan5. [1] A. Drăgulescu, V.M. Yakovenko, Statistical Mechanics of Money, The European Physical Journal B 17 str. 723-729 (2000.). [2] V. Pareto, Cours d´Economie Politique, Lausanne. (1897). [3] K. Biljaković, D. Nestić, B. Podobnik, Raspodjela Dohotka u Hrvatskoj u Svjetlu Zakona Statističke Fizike, Financijska teorija i praksa 27 (2) str. 213-222 (2003.). [4] A. Drăgulescu, V.M. Yakovenko, Exponential and Power-law Probability Distributions of Wealth and Income in the United Kingdom and the United States, Physica A 299 str. 213-221 (2001.). [5] W. Suoma, Universal Structure of the Personal Income Distribution, www.lanl.gov/cond-mat/0011373 (2000.).