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Strontium-doped lanthanum manganites, described with the general formula La1-xSrxMnO3 (LSMO) are attractive, among others, for use in magnetic refrigeration and data storage due to their remarkable magnetic and electric properties at room temperature. In this study, LSMO powders were prepared by the citrate-nitrate autocombustion (CNA) and coprecipitation synthesis to investigate how the synthesis procedure impacts the structural characteristic of the materials. Both synthesis methods yielded materials with rhombohedral crystal structures. The lattice parameters and atoms occupancy factors were determined by Rietveld refinement analysis. The oxygen nonstoichiometry was determined by permanganate titration and the amount of Sr-dopant was confirmed by energy-dispersive X-ray spectroscopy. The obtained results showed that target Sr-doping was achieved and that materials prepared by coprecipitation possessed higher oxygen nonstoichiometry in comparison to the materials prepared by CNA. The magnetization curves as a function of temperature were recorded in a temperature range of 2-400 K at applied magnetic fields of 10 Oe, 100 Oe and 1000 Oe for all prepared materials. The Curie temperatures (TC) increased with increasing Sr-doping meaning that materials with x ≥ 0.2 are suitable for room-temperature applications as ferromagnets. Furthermore, Sr-doped materials showed low remanent magnetization making them applicable as soft ferromagnets. For materials prepared by coprecipitation, a large magnetic entropy change was observed near TC. The maximum entropy changes of 1.5 and 1.3 J kg-1 K-1 were observed for LSMO materials with x = 0.1 and 0.2 at temperatures of 381 K and ~400 K, respectively. These two materials had the highest oxygen nonstoichiometry leading to the increase of Mn4+/Mn3+ mixed valences ratio and overall crystal lattice entropy, accompanied by magnetic phase transitions around room temperature. Therefore, coprecipitation synthesis is presented as an efficient synthesis method of manganites leading to the structural defects, i.e., oxygen nonstoichiometry resulting in improved overall magnetic properties.

Heteropolynuclear metal complexes have been extensively studied for their ability to form various architectures and topologies, from discrete polynuclear metal compounds to polymeric one- (1D), two- (2D) or threedimensional (3D) assemblies, featuring a range of distinct magnetic properties. In recent decades, the chemistry of oxalate-containing complexes has become an active area of research – the oxalate moiety, C2O42−, acts as a linker between metal centres with various possibilities of bridiging modes and has the ability to mediate magnetic interactions between paramagnetic metal centres. Stable mononuclear anionic oxalate complexes such as tris(oxalato)metalate anions, [MIII(C2O4)3]3− (MIII = Mn, Cr, Fe, V), are often used as ligands toward another metal ion for the preparation of extended multifunctional systems. Also, the introduction of organic ligands containing N- donors into the metal–oxalate systems also influences the nuclearity of the metal centres and additionally stabilizes their solid-state structures. Applying the layering technique, crystals of the tetranuclear chloride-bridged compounds [Cu4(terpy)4Cl5][M(C2O4)3]·nH2O M = Cr3+ ; n = 9 (1) and M = Fe3+ n = 10 (2)] grew from the reaction of an aqueous solution of K3[Cr(C2O4)3]·3H2O or K3[Fe(C2O4)3]·3H2O, respectively, methanol solution containing CuCl2·2H2O and a tridentate ligand 2, 2′:6′, 2′′- terpyridine (terpy). When Cu(NO3)2·3H2O was used instead of the chloride salt, unexpected change in type of the bridge, oxalate versus chloride, was achieved and crystals of the 1D oxalate-bridged coordination polymers {; ; [Cu4Cr2III(H2O)2(terpy)4(C2O4)7]·10H2O}; ; n (3) and {; ; [CuII2FeIII(H2O)(terpy)2(C2O4)7/2]·6H2O}; ; n (4) together with compound [CuII2(H2O)2(terpy)2(C2O4)] [CuIIFeIII(CH3OH)(terpy)(C2O4)3]2 (5), respectively, have been formed. Further, two polymorphs of 3D coordination polymer [CuIIFeII2(H2O)(terpy)(C2O4)3]n (6a and 6b), crystallizing in the triclinic (a) and monoclinic (b) space groups, were formed hydrothermally, depending on whether CuCl2·2H2O or Cu(NO3)2·3H2O was added to the water, besides K3[Fe(C2O4)3]·3H2O and terpy, respectively. Compounds 1 and 2 exhibit a ground-state spin of 1, which is due to antiferromagnetic and ferromagnetic interactions of Cu2+ ions across the chloride bridges in the tetramers ; ferromagnetic coupling transferred through the oxalate bridge was found between Cu2+ ions in 3, as well as strong antiferromagnetic coupling of the Cu2+ ions mediated by the oxalate ligand in cation moiety, and weak ones between Cu2+ and Fe3+ ions through oxalate bridge in the anion of compound 5. Polymer 6 exhibits an antiferromagnetic phase transition at 25 K

Design of new materials with targeted physical properties is a very atractive field of research nowadays. In recent years, the structural diversity of metal-organic coordination systems has paved the way for the development of multifunctional materials that combine two or more different properties, especially magnetic and electrical ones. A very important role in the design and synthesis of such materials belongs to the oxalate moiety, C2O42-, due to its various possibilities of coordination to metal centres and its ability to mediate electronic effects between paramagnetic metal ions. The synthetic strategy for the preparation of (hetero)polynucelar species is "building block chemistry", in which a molecular anionic ligand, very often the tris(oxalato)metalate anion [MIII(C2O4)3]3− (MIII = Cr, Fe, Ru, Rh, Mn or V), is used as a ligand towards other metal cations. Starting from the same reactants, the structural uncertainty of the obtained coordination compounds can lead to two basic cases: (i) both the structures and the chemical compositions are different ; the obtained compounds differ significantly from each other, reflecting the great versatility of a self- assembly system ; (ii) the structures are different, but the whole coordination networks have the same chemical composition, when the obtained compounds are classified as supramolecular isomers.[1] Inspired by the structural versatility of oxalate-based [CuFe] compounds containing 2, 2':6', 2"-terpyridine (terpy)[2], seven novel oxalate-based [CuIICrIII] compounds: [Cu4(terpy)4Cl5][Cr(C2O4)3]·9H2O (1 ; terpy = 2, 2′:6′, 2′′-terpyridine), {; ; [Cr2Cu4(H2O)2(terpy)4(C2O4)7]·10H2O}; ; n (2), [Cr2Cu4(H2O)2(terpy)4(C2O4)7]·12H2O (3), [Cu(H2O)3(terpy)][CrCu(H2O)(terpy)(C2O4)3]2·9H2O (4), [Cu(H2O)(terpy)(NO3)][CrCu(H2O)(terpy) (C2O4)3]·6H2O (5), [CrCu2(terpy)2(C2O4)3(NO3)2]·1.5H2O·CH3OH (6) and [Cr2Cu4(H2O)4(terpy)4(C2O4)6] [Cr2Cu2(terpy)2(C2O4)6]·10H2O (7) were obtained from the reaction of an aqueous solution of the building block [Cr(C2O4)3]3− and a methanol solution containing Cu2+ ions and the terpyridine ligand by the layering technique. Interestingly, changing only the anion of the starting salt of copper(II), NO3− instead of Cl−, resulted in an unexpected change in the bridge type, oxalate (compounds 2−7) versus chloride (compound 1), which affected the overall structural architecture. Compounds were studied by single- crystal X-ray diffraction, IR spectroscopy, magnetization measurements and density functional theory (DFT) calculations.

Removal of organic pollutants from the waste water will bethemost challenging objective in the future. The photodegradation using the zinc oxide (ZnO)is one of the bestpromising material due to low price and high efficiency. Zinc oxide nanoparticles were synthetized by self propagatingroom temperature reaction of zincnitratewith sodium hydroxide.After reaction powder wascalcinated at 1100°C for 4 h in furnace. The diffraction patterns were recorded at room temperature and atmospheric pressure in the absence of any re-heating of the samples. The temperature dependence of magnetization was measured in the field of 1000 Oe and temperature range from 2 to 300 K using MPMS5 SQUID magnetometer. Photocatalytic properties were determined using the degradation of organic dye Methylene Blue (MB). Hg UV lap was used for irradiating the solution of MB and ZnOnanopowder. The photodegradation of MB was monitored by decreasing 664 nm peak during 120 min, after this period of time we observed 95% of reduction from the starting dye concentration. Nanopowder of ZnO show strong photocatalytic performance and can be used for further investigation and applications. IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrade

Multiferroic guanidinium copper(II) formate, [C(NH2)3][Cu(HCOO)3], belongs to the family of metal organic perovskites with the formula ABX3. It crystallizes in the orthorombic space group Pna21 and consists of copper – formate 3D framework with guanidinium cations in its nearly cubic cavities. Due to the Jahn-Teller effect of Cu2+ ion, the octahedral coordination is elongated, producing the framework of Cu-formate chains in the c direction, where Cu2+ ions inside the chain are linked with short bonds and Cu ions between the chains with the long bonds. We have studied magnetic properties of [C(NH2)3] [Cu(HCOO)3] using MPMS5 SQUID magnetometer. Temperature dependence of magnetization showed a broad peak centered at 45 K which can be ascribed to antiferromagnetic order in the Cu-formate chains. Below 4.6 K the sharp rise of magnetization indicated a formation of 3D spin canted antiferromagnetic long range order. Hysteresis loops at the temperatures below 4.6 K showed a sharp increase of magnetization for the fields lower than 50 Oe. Anisotropy could be seen in both M(T) and M(H) measurements. The effect of electric field on the magnetization was observed at temperatures below 4.6 K as a difference in magnetization curves measured with and without the applied electric field, pointing to the existence of substantial magnetoelectric coupling. Search for the explanations of observed magnetic and magnetoelectic behaviour is in progress considering the interesting crystal structure of this compound. Wishing for better understanding we are collaborating with other scientists doing the complementary research such as the ab-initio calculations and torque anisotropy measurements. It would also be interesting to do electron paramagnetic resonance experiments and optical measurements in order to see if there is magnetoelectric response at much higher frequencies making it possible choice for the application as a fast magnetoelectric.

Due to the rich variety of metal species and ligands, coordination geometry, guests inside the pores, and supramolecular structures, an enormous number of coordination polymers with various structures, dimensionality, and nuclearity have been synthesized and reported. This area of molecular chemistry is the basis for design of the molecule-based materials that combine two (or more) physical properties of interest, especially upgrading and expanding the molecular magnetism toward multifunctional systems. Most of the oxalate-based molecular magnets described to date have been obtained by the “complex-as-ligand approach” ; a molecular building block, the tris(oxalato)metalate [MIII(C2O4)3]3 anion is used as a ligand toward other metal cations. The topology of these oxalate-bridged compounds is controlled by a templating counterion. Two polymorphs of 3D coordination polymer [CuIIFeII2(H2O)(terpy)(C2O4)3]n (1 ; terpy = 2, 2′:6′, 2′′-terpyridine), formed hydrothermally, contain homometallic 2D oxalate-bridged honeycomb anionic layers, [FeII2(C2O4)3]n2n-, mutually linked by complex cations of copper(II) ions, [Cu(H2O)(terpy)]2+, through oxygen atoms from oxalate bridges. Recently published oxalate-based networks have shown proton conductivity related to the presence of ammonium and/or crystallization water [1]. Therefore, in addition to magnetic, electrical properties of 1 have been also investigated ; it exhibits antiferromagnetic phase transition at 25 K and proton conductivity. Furthermore, the ability of this 3D polymer, due to their appropriate stoichiometry of metal ions, to act as single-source precursor for the formation of spinel CuFe2O4 oxide by heat treatment has been explored [2].

Metal-organic compounds with perovskite crystal structure provide a fertile playground for design of the multifunctional materials. Some properties can be mutually dependent, and some orders mutually coupled, paving the way to design of the magnetoelectric multiferroics. Interesting example of the hybrid layered perovskite multiferroic is ethylammonium tetrachlorocuprate, which consists of the ferromagnetic layers of corner sharing [CuCl4]2− octahedra connected by two layers of polarizable organic ions of C2H5NH3+. Besides the known ferroelectric transition around 245 K, it shows rich magnetic behaviour below 10.5 K, including magnetic anisotropy and transitions between different magnetic states. Although the search for magnetoelectric effect was not successful, a slight change of magnetization with the structural changes above 300 K was observed. Composition of this metal- organic perovskite was changed and the accompanied changes of the crystal structure and magnetic properties were studied. Up to now, magnetization is measured in DC regime using SQUID magnetometer in temperature range 2–300 K at different magnetic fields up to 5 T. Large impact of geometric and electronic changes of the organic cation structure on magnetic properties was observed in following two groups. Novel series of the solid-state architectures consisting of tetrachlorocuprate units and ortho-, meta- and para-anisidinium were prepared and in their crystal structure considerable change of geometry was observed: from the discrete square planar tetrachlorocuprate anions in the ortho- anisidinium compound to the Ruddlesden-Popper perovskite phase with slightly distorted layers built from CuCl6 octahedra in the para- anisidinium compound. Spins 1/2 per Cu2+ ion remain in the paramagnetic state down to the lowest temperatures in the ortho-anisidinium tetrachlorocuprate. However, there are transitions to the ferromagnetic state measured at 4.2 K and 9.5 K for the meta-anisidinium and para-anisidinium tetrachlorocuprates, respectively. Their ferromagnetic-like hysteresis loops are very soft, without the observable coercivity. Surprise happens in difference between the chloroethylammonium tetrachlorocuprate and bromoethylammonium tetrabromocuprate: the first one has antiferromagnetic transition at 7.8 K with metamagnetic transition in fields above 150 Oe, while the second one has ferromagnetic transition at 11 K and broad hysteresis loop with coercivity around 100 Oe at 2 K. Polar order is predicted in theoretical calculations, and magnetoelectric experiments could be challenging. This research showed that a small change in structure has drastic influence on the geometry and magnetism of the cuprate units. At the moment it seems to us that the 3D metal-organic perovskites have brighter perspective for magnetoelectric coupling than the 2D. If having on mind wide possibility of combining the building blocks with different physical properties like elastic, (super)conducting, optical, polar, magnetic, the rich field of applications can be foreseen for 2D perovskites, including also influence of the the light on the magnetic and electric response. Some of those will be of our future interest.

Magnetic hysteresis curves for CoxMg1-xFe2O4 compounds with x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1 were recorded using the Vibrating-Sample Magnetometer (VSM) model PAR/EG&G 4500. Samples in powder form were pressed in the gelatin ampoule which was tightly fastened to the sample rod, in order to avoid the rotation of the powder. Measurements were performed at room temperature, with maximum magnetic field of 10 000 Oe (1T). Constant magnetic field sweep rate of 1000 Oe/min was used and for each measured curve 1 000 data points were collected. Driving frequency of the sample and integration time were 82 Hz and 100 ms, respectively. For every sample, we also measured ZFC and FC curves in constant magnetic field of 100 Oe, in temperature range from 80 °C to 600 °C. Because of high temperatures, samples were placed in ampoule made of boron nitride, which is thermally stable and non-magnetic. Measured magnetic hysteresis show monotonous development with Mg-Co substitution. Increase of magnetization happens with substitution of diamagnetic Mg2+ ions with cobalt ions. Results show almost linear dependence of remanence magnetization, coercive field and magnetization in field of 10 kOe on concentration of Co (Mg). Slightly larger deviation for sample with x=0.9 is in agreement with other anomalies observed for this concentration, like density. Values for pure Co and Mg ferrites are in good agreement with existing data, for example, saturation magnetic moments listed in [1] are 1.1μB for MgFe2O4 and 3.7μB for CoFe2O4 . Coercive field increases with cobalt content, which can be understood as a consequence of stronger spin-orbit coupling leading to larger anisotropy and therefore to harder reversal of their magnetic moments, causing stronger pinning of the domain walls, i.e. more difficult change of magnetic domain structure. The same reasoning applies to the remanence magnetization. Recorded ZFC and FC curves allowed for accurate determination of phase transition temperatures, as well as of critical exponents which are in a good agreement with theoretical values. For some of the samples additional hysteresis curves were recorded at the temperatures slightly below and above the transition temperature, demonstrating a clear difference between ferrimagnetic and paramagnetic phase.

Coordination polymers with metal-organic frameworks and organic or inorganic functional cations offer many possibilities in constructing interesting multifunctional materials such as ferromagnetic conductors, photo and piezo switching magnets, chiral magnets and multiferroics. Especially interesting are oxalate-based compounds, where the C2O42-acts as a linker between metal centres and provides various possibilities of coordination to metal centres resulting in structures with different dimensionalities. The other useful property of oxalate ions is their ability to mediate super-exchange interaction.In this work we will present magnetic behaviour of three novel metal-organic coordination polymers synthetized by a layering technique. The investigated compounds consist of single or multi metal cations bridged by an oxalate ion. The first compound, {; ; Mn(bpy) (C2O4) ·1.5H2O }; ; n, has a 1D chain structure, where the chains are connected by πinteractions between 2, 2’ bipyridyl molecules coordinated on the manganese ions of neighbouring chains. The second compound, {; ; [CrCu(bpy)(C2O4)3] [CrCu3(bpy)3(CH3OH)(H2O) (C2O4)4]·CH2Cl2·CH3OH·H2O}; ; n , consists of two kinds of chains in which two metal ions, chromium and copper ions, are bridged by the oxalate ion. The 2, 2’-bipyridyl molecules are coordinated on the copper ions, enabling the existence of πinteraction between the chains. One chain consists of only Cu and Cr ions bridged by oxalate, while the other chain has two more Cu atoms connected to the Cr ion. The third compound, {; ; [CaCr2Cu2(phen) (C2O4)6]n·4CH3CN·2H2O}; ; n, is a two dimensional coordination polymer which consists of copper, chromium and calcium ions bridged by the oxalate bridge in the 2D network. The molecule coordinated on the copper is a 1, 10- phenanthroline. The magnetic properties of polycrystalline samples in powder form were investigated using a MPMS5 SQUID magnetometer. Temperature dependence of magnetization was measured in the temperature range 2 -400 K, measuring both zero field cooled (ZFC) and field cooled (FC) magnetization curves. The MT curve of a single metal chain compound showed a broad peak at 15K, characteristic of antiferromagnetic chains, while the other two compounds show curves similar to the paramagnetic ones, with no maximum, or saturation at low temperatures, indicating a more complex magnetic coupling. The field dependence of magnetization was measured up to 5 T. The MH curve for the first compound is almost linear with no saturation, characteristic of antiferromagnetic chains, and the value of 1.1 μB/f.u. at 5T and 2K. The second and third compound show saturation of the magnetization at the value of 8 and 7 μB/f.u. respectively, indicating ferromagnetic or ferrimagnetic coupling of Cu and Cr ions.

In the research of multifunctional properties, one of the most important targets is a thorough understanding of a correlation between structural features of material and desired physical and chemical properties. High thermal stability makes BaAl2O4 suitable for fabrication of fluorescent lamps, LEDs, FEDs, etc. – this especially refers to doped BaAl2O4 due to optimal combination of microstructural, electrical, and optical parameters [1]. Physical properties of BaAl2O4 host can be controlled by modification of crystal structure and electronic state by partial substitution of Al and Ba sites cations and/or thermal treatment under reduction conditions [2]. The influence of Co2+ on the BaAl2O4 lattice and its magnetic properties was explored using the PXRD, Uv-Vis and magnetic studies. Magnetization measurements of BaAl2O4 doped with 4, 8 and 12 at. % Co in form of pressed pellets were performed using SQUID magnetometer at temperatures 2 - 400 K and fields up to 5 T. We found that by increasing the amount of Co, resulting magnetization also increases in otherwise non-magnetic BaAl2O4 material. In order to describe magnetic behaviour, it was necessary to include magnetic anisotropy of paramagnetic Co2+ ions. Since BaAl2O4 is ferroelectric [3], very motivating is similar work where Fe doping of ferroelectric BaTiO3 produced also the magnetic response of material [4]. If considerable magnetic response could be obtained, it could lead to the novel magnetoelectric and/or multiferroic state in doped BaAl2O4.

Standardizacija Europskih pravila letenje (engl. Standardised European Rules of the Air - SERA) predstavlja propis kojim se objedinjuju pravila letenja, te bi kao takav propis trebao pomoći državama ĉlanicama u unificiranju standarda i jedinstvene implementacije procedura u europskom zraĉnom prometu. Implementacijom se nastoji povećati sigurnost zraĉnog prometa i minimalizirati opasnosti koje su prouzroĉene vlastitim nacionalnim pravilima letenja koje provode pojedine ĉlanice Europske unije. Ovim radom se vrši komparativna analiza dokumenta SERA-e i zakonodavnog okvira Republike Hrvatske, te se prikazuju odstupanja od nacionalnog zakonodavnog, MeĊunarodne organizacije civilnog zrakoplovstva (engl. International Civil Aviation Organisation - ICAO) i europskog regulatornog okvira.

Cobalt/magnesium ferrites with various mole percentage ratio of the metals (obtained structures are CoxMg1-xFe2O4 with x being 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized by sol-gel combustion synthesis using glycine as fuel, following the rules of propellant chemistry. The powders were then sintered at 700 °C for 3 hours. Obtained powders were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, UV/vis diffuse reflectance spectroscopy (DRS). Investigation of the magnetic properties was also conducted by vibrating sample magnetometry (VSM). The obtained powders were proved to be phase-pure cubic spinels which formed agglomerated micrograins. Series of photocatalytic experiments of methylene blue degradation were done. The influence of different experimental conditions was investigated including variations of: pH values, concentrations of the pollutant, masses of the photocatalyst, different light sources and therefore different light irradiation. Interesting results, including enhancement of the degradation rate with the introduction of cobalt into MgFe2O4 and decrease of the degradation rate with further increase of cobalt content and formation of hard agglomerates, open new possibilities for further investigation of the utilisation of Co/Mg ferrites as photocatalysts.

U ovom radu bavimo se potragom za polariziranim zračenjem radiogalaksija koristeći polarimetrijska promatranja na 150 MHz prikupljena LOFAR teleskopom u području centriranom na sjajnoj radiogalaksiji 3C196 (RA = 8h13m36s, DEC = +48°13'03'') koje obuhvaća oko 50 kvadratnih stupnjeva. Ukupno smo pronašli 10 polariziranih radioizvora. Analizom slika iz FIRST kataloga na 1.4 GHz ustanovili smo da su 9 izvora radiogalaksije FR-II tipa koje su luminoznije prema rubovima, a preostali izvor je kvazar. Izračunati postotci polarizacije izvora na 150 MHz pokazuju znatno veću depolarizaciju u odnosu na mjerenja iz NVSS kataloga na frekvencijama oko 1.4 GHz. Za pojedine izvore postoje velike razlike između Faradayevih dubina dobivenih iz LOFAR-ovih mjerenja i onih koje se navode u NVSS katalogu, što pripisujemo niskoj rezoluciji u Faraday prostoru za NVSS-ova mjerenja. Usporedbom dobivenih vrijednosti ukupnog intenziteta s onima na drugim frekvencijama, koje smo pronašli u VLSS (74 MHz), NVSS (1.4 GHz) i WENSS (325 MHz) katalozima, dobili smo vrijednosti spektralnih indeksa koji u prosjeku iznose 0.753. Dobivena je gustoća od jednog izvora na 5 kvadratnih stupnjeva neba. In this Diploma thesis we are searching for polarized emission of the radio galaxies in a field centred at a bight radio galaxy 3C196 (RA = 8h13m36s, DEC = +48°13'03''), covering an area of 50 square degrees. In our analysis we are using LOFAR polarimetric observations at 150 MHz. In total we have found 10 polarized radio sources. By analysing the FIRST images of these sources we concluded that one source is a quasar, while all the others are FR-II radio galaxies, which are the brightest at the edges. Their degree of polarization at 150 MHz is smaller than at 1.4 GHz (NVSS catalogue), due to significantly higher wavelenght dependent depolarization. There is some discrepancy in obtained rotation measures if compared with the ones at 1.4 GHz. This can be attributed to much poorer resolution in Faraday depth at higher radio frequencies. We also compared the amount of emission obtained in total intensity with catalogues at other frequencies (VLSS - 74 MHz, WENSS - 325 MHz, NVSS - 1.4 GH). Based on this comparison we calculated the spectral indices of the sources, mounting to 0.753 in average. We found a density of 1 source per 5 square degrees.