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We present the result of a systematic study of electrical resistivity, superconductive transitions and Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals in a broad composition range x (0.1-0.5). All samples showed a high resistivity at room temperature (140-240 μΩ cm) and the superconducting transition temperatures decrease with increasing TL content, similar to binary amorphous [3] and crystalline HEA TE-TL alloys [4]. With the highest recorded transition for (TiZrNbCu)0.90Co0.10 at 1.94 K. The Hall coefficient RH is temperature independent and positive for all samples except for (TiZrNbCu)0.57Co0.43 with an interpolated critical concentration at xc=0.34, in good agreement with binary TE-TL alloys [1]. For the temperature dependence of resistivity, we discuss possible variable range hopping (VRH) like parallel conduction mode, in temperature range 30-150K, with an exponent p=1/2. We examine this in the context of VRH in granular materials [2]. References: [1] J. Ivkov and E. Babić, J. Phys.: Condens. Matter 2 (1990) 3891 [2] V. F. Gantmakher, Electrons and Disorder in Solids (OUP Oxford, 2005). [3] E. Babić et al, Solid State Commun. 39 (1981) 139 [4] K. Stolze et al, Chem. Mater. 30 (2018) 906

Using a He3 cryostat in a superconducting magnet with fields up to 16 T, superconductivity of (TiZrNbCu)1-xNix and (TiZrNbNi)1-xCux metallic glasses was studied over a broad concentration range from the high entropy alloys (HEA) region to the Ni- and Cu-rich alloys, respectively. We have observed that the upper critical fields of these alloys are Pauli limited and that the superconducting transition temperatures follow the behaviour of the dressed density of states at the Fermi level Nγ(EF), which is common in transition metals and their alloys [1]. In particular, we have shown that the electron-phonon coupling constant λe-p is proportional to the band density of the state at the Fermi level in our alloys, but also crystalline HEAs [2-4], and in other transition metal alloys. This addresses the problem of unusual superconductivity behaviour [4] which was attributed to the chemical complexity of HEAs but is shown to be inherent to transition metals. Although, minor complications do arise from combining metals of different transition series. [1] R. C. Dynes, C. M. Varma, J. Phys. F Met. Phys. 6 (7) (1976) L215-L219 [2] P. Koželj et al, Phys. Rev. Lett. 113 (10) (2014) 107001 [3] S. Vrtnik et al, J. Alloy. Compd. 695 (2017) 3530– 3540 [4] F. von Rohr et al, Proc. Natl. Acad. Sci. 113 (46) (2016) E7144–E7150

We present results of comprehensive study of electronic properties of (TiZrNbCu)(1-x)Ni(x) metallic glasses performed in broad composition range x encompassing both, high entropy (HE) range, and conventional Ni-base alloy concentration range, x >= 0.35. The electronic structure studied by photoemission spectroscopy and low temperature specific heat (LTSH) reveal a split-band structure of density of states inside valence band with d-electrons of Ti, Zr, Nb and also Ni present at Fermi level N(E_F), whereas LTSH and magnetoresistivity results show that variation of N(E_F) with x changes in Ni-base regime. The variation of superconducting transition temperatures with x closely follows that of N(E_F). The electrical resistivities of all alloys are high and decrease with increasing temperature over most of explored temperature range, and their temperature dependence seems dominated by weak localization effects over a broad temperature range (10-300 K). The preliminary study of Hall effect shows positive Hall coefficient that decreases rapidly in Ni-base alloys., 32 pages, 6 figures

La1-xCaxMnO3 belongs to the family of manganites, with generalized chemical formula R1-xAxMnO3, where R element is a rare earth element, and A is alkaline, alkaline earth or Pb. These compounds became very interesting in 1994, due to the discovery of colossal magnetoresistance (CMR). CMR was originally found for 0.2 < x < 0.5, and therefore that part of the phase diagram was mostly investigated. Here we report our results obtained in the overdoped part of the diagram 0.5 ≤ x ≤ 0.75 on La1-xCaxMnO3 thin films grown on MgO substrate. We have found CMR and metastable behavior deep in the overdoped part, which we attributed the existence of FM clusters in the AFM / CO insulator state.

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.

We present the results of ongoing comprehensive study of the electronic properties of (TiZrNbCu)1- xNix metallic glasses performed in a broad composition range x encompassing both, the high entropy (HE) range, x ≤ 0.25, and conventional Ni- base alloy concentration range, x ≥ 0.35. The electronic structure (ES) studied by photoemission spectroscopy and low temperature specific heat (LTSH) [1] reveal the split-band structure of the density of states (DoS) inside the valence band with the d- electron of Ti, Zr, Nb and also Ni present in DoS at the Fermi level N(EF), whereas LTSH and present magnetoresistivity results show that variation of N(EF) with x changes in Ni-base regime. The variation of the superconducting transition temperatures, TC ≤ 1.6 K with x closely follows that of N(EF) as is usual in disordered transition metal alloys [2]. The electrical resistivities of all alloys are high (> 150 µΩ cm) and accordingly decrease with increasing temperature over most of the explored temperature range, and their temperature dependence seems dominated by the weak localization effects over a broad temperature range (10 – 300 K). The preliminary study of the Hall effect shows that the Hall coefficient RH > 0 and in the HE concentration range change little with x. The results are compared with these for corresponding binary metallic glasses. [1] I. A. Figueroa, et al., J. Alloys Compd. 745, 455 (2018) [2] E. Tafra, et al., J. Phys.: Condens. Matter 20, 425215 (2008)

Heuslerove slitine na bazi Co privukle su veliki interes kao kandidati za primjenu u spintronici. Neki od ovih materijala karakteriziraju se kao polu-metalni (half-metal) feromagneti s visokom Curievom temperaturom i polarizacijom spina struje [1]. Jedan od takvih je Co_2TiSn [2, 3]. Za ovaj materijal teorijska istraživanja predvidjela su postojanje topološkog semimetalnog stanja s Weylovim čvorovima koji se javljaju za određene smjerove magnetizacije, što bi trebalo rezultirati velikim magnetootporom i anomalnim Hallovim efektom [4] te da je glavni doprinos intrinsičnom anomalnom Hallovom efektu rezultat pojave Berryeve zakrivljenosti [5]. U ovom radu predstavljamo sistematsko istraživanje otpornosti, magnetootpora i Hallovog efekta Co_2TiSn i Co_2Ti_0.6V_0.4Sn tankih filmova na više temperatura i za magnetska polja do 16 T primijenjena duž odabranih kristalografskih smjerova. Oba sustava pokazuju veliki anomalni Hallov efekt, ali ipak manji nego što je za neke standardne feromagnetske slitine. Izmjerena anomalna Hallova vodljivost za Co_2TiSn manja je od drugih rezultata [5], ali još uvijek u skladu sa teorijski izračunatom vrijednošću [5]. Za Co_2Ti_0.6V_0.4Sn anomalna Hallova vodljivost je znatno niža. Za oba sustava dominantni doprinos anomalnom Hallovom efektu dolazi od intrinsičnog side-jump efekta, što je u skladu sa teorijskim predviđanjima [6] za sustave s visokom otpornošću. Magnetoopor za oba sustava je malog iznosa (

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.

The family of compounds based on bis-(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecule shows intriguing phenomena such as unconventional superconductivity, charge ordering, Mott transition, antiferromagnetism, incoherent metallic state etc. κ-(BEDT-TTF)2Cu2(CN)3 member is especially interesting because it is considered as one of the first realizations of a quantum spin liquid. It has a layered crystal structure consisting of conducting BEDT-TTF layers sandwiched between insulating Cu2(CN)3 layers and according to the phase diagram is in a Mott insulating state. However, approaching the spin liquid ground state various anomalies were observed showing that κ-(BEDT-TTF)2Cu2(CN)3 is not an ordinary Mott insulator. Here we present DC resistivity, Hall effect and magnetoresistance measurements for 10 K < T < 300 K and in magnetic fields up to 5 T on high quality κ-(BEDT-TTF)2Cu2(CN)3 single crystals. Our results clearly show that at lower temperatures (T < 130 K) charge transport takes place via variable range hopping, a mechanism typical for disordered systems. The origin of disorder, in nominally clean single crystals, can be found in insulating Cu2(CN)3 layers since some CN groups lie in centers of inversion and are therefore crystallographically disordered. The CN disorder affects conducting layers via hydrogen bonds between CN groups and ethylene groups of the BEDT-TTF molecules.

La1-xCaxMnO3 pripada obitelji manganovih oksida, preciznije manganita, s općenitom kemijskom formulom R1-xAxMnO3, gdje je R element rijetke zemlje, a A alkalni, zemnoalkalni metal ili Pb. Ovi spojevi se istražuju još od 1950., ali postaju posebno interesantni 1994., zbog otkrića kolosalnog magnetootpora (CMR). Osim toga, manganiti imaju vrlo bogate fazne dijagrame, s mnogim zanimljivim fenomenima. Istraživani spoj La1-xCaxMnO3 ima tri najvažnija (i najveća) dijela faznog dijagrama: paramagnetsko (PM) izolatorsko stanje na visokom temperaturama, feromagnetsko (FM) metalno stanjeza 0.2 < x < 0.5 (koje je povezano s CMR) i antiferomagnetsko (AFM) izolatorsko stanje, popraćeno uređenjem naboja (CO) za 0.5 < x < 0.87. Danas se vjeruje da u nekim dijelovima faznog dijagrama može doći do koegzistencije faza, posebno u blizini granice faza. Najzanimljivija je granica između FM metalnog stanja i AFM/CO izolatorskog stanja na x = 0.5. Nedavno smo objavili naše rezultate istraživanja magnetotransportnih svojstva tankih filmova manganita La1-xCaxMnO3, za x = 0.52, 0.58 i 0.75. Za koncentracije x = 0.52 i 0.58, opazili smo pojavu CMR (karakterističnu za x < 0.5), a koju smo pripisali postojanju FM klastera u AFM/CO izolatorskom stanju. Efekt je najizraženiji za x = 0.52, gdje dolazi do prijelaza u metalno stanje pod utjecajem magnetskog polja. Inače, ovisnost otpornosti o temperaturi bez primjene magnetskog polja, za sve tri koncentracije i na nižim temperaturama (T < TCO), slijedi režim trodimenzionalnog (3D) Mottovog preskoka promjenjivog dosega (VRH). Objavljeni rezultati su prošireni mjerenjima do nižih temperatura i jačih magnetskih polja, a također smo obuhvatili još različitih koncentracija, pri čemu su opažene i neke nove pojave: velike razlike između otpornih krivulja mjerenih u magnetskom polju, u slučajevima kad je uzorak hlađen u magnetskom polju (FC) i bez magnetskog polja (ZFC). Osim toga otporne krivulje pokazuju značajne efekte ovisne o povijesti mjerenja i neobične vremenske relaksacije.

Ferromagnetic Heusler alloys are characterized by high Curie temperatures and a great variety of electronic and magnetic properties. The Co-based Heusler alloys are of a particular interest, as half-metallic ferromagnets with a high spin polarization at Fermi energy they have a great potential for spintronic applications (for example, as magnetic electrodes in magnetic tunnel junctions). Recently, a theoretical study [1] has predicted a topological semimetal state in Co2TiSn with Weyl nodes appearing for certain magnetization directions, which could result in a large magnetoresistance and anomalous Hall effect. We have performed a detailed study of the resistivity, magnetoresistance, and Hall effect of Co2TiSn and Co2Ti0.6V0.4Sn Heusler alloys at several temperatures and with the magnetic field applied along selected crystallographic directions. Our data show that the anomalous Hall effect conductivity is large, in the range of the AHE conductivity found in Mn3Ge [2], while the magnetoresistance is small and quasi-isotropic without any unusual dependences on the field orientation with respect to the crystal axes. Although the results do not show a specific and clear signature of a Weyl character, they recognize the potential of the Co2TixV1-xSn system for future spintronic device applications. [1] G. Chang et al, Sci. Rep. 6 (2016) 38839. [2] A. K. Nayak et al, Sci. Adv. 2 (2016) e1501870.

The quest for exotic electronic orderings is driven by our ability to produce said states as cleanly as possible, in a tunable manner and preferably cheap. Organic conductors with reduced dimensionality offer all of these desirable properties as their rich phase diagrams are created by the competition between the tendency of electrons to delocalize and the pronounced interactions between charge, spin and lattice. We discuss here the organic charge-transfer salt α-(BEDT-TTF)2I3, a highly anisotropic material whose phase diagram features a number of intriguing quantum effects, most notably at ambient pressure it undergoes a metal-to-insulator transition into a charge-ordered (CO) state with CO-induced ferroelectricity. The electronic behavior in the CO phase and its exact microscopic underpinnings are however still under heated discussion. As an intriguing link to Mott-like spin-liquid systems from the same family of salts, the dielectric response and structural considerations point toward the important role of disorder. Here we show a detailed systematic study of the titular compound at ambient pressure above and below the CO phase transition, in particular of its dielectric properties both in-plane and out-of-plane, resistivity, Hall effect and magnetoresistance. In the high-temperature semimetallic phase, dominant inter-pocket scattering equalizes mobilities of the electrons and holes creating an almost temperature-independent conductivity as well as a low Hall effect. At low temperatures, within the insulating charge-ordered phase dc transport, magnetoresistance, as well as dielectric response show fingerprints of disorder whose origin is found in the anion layers tightly hydrogen-bonded to the conducting BEDT-TTF molecules.

Većina konvencionalnih slitina sastoji se od jednog, ili u rijetkim slučajevima dva, osnovna metala kojima se dodaju male količine drugih metala i/ili nemetala kako bi se poboljšala njihova svojstva. U posjednih nekoliko godina veliku pažnju pak privlači novi tip slitina, tzv. slitine visoke entropije (eng. High-entropy alloys - HEA). Ove slitine su građene od velikog broja (=>5) elemenata u približno ekvimolarnom omjeru [1, 2]. Ovakva građa otvara potencijal za istraživanje velikog broja novih slitina raznih struktura i svojstava [3]. Nedavno su objavljeni rezultati [4] opsežnih istraživanja četiri (TiZrNbCu)_1-xNi_x(x

alpha-(BEDT-TTF)2I3, gdje BEDT-TTF označava organsku molekulu bis-(ethylenedithio)- tetrathiafulvalene, pokazuje mnoštvo intrigantnih fenomena kao što su metal-izolatorski prijelaz, uređenje naboja, elektronska feroelektričnost, nekonvencionalna supravodljivost, Diracovi fermioni itd. Prema faznom dijagramu alpha-(BEDT-TTF)2I3 pri atmosferskom tlaku na 135 K prelazi iz polumetalnog u stanje uređenja naboja (CO) što je popraćeno otvaranjem energijskog procjepa u nabojnom i spinskom sektoru. Mnoge fizikalne veličine doživljavaju skok na 135 K, a mjerenja specifične topline pokazuju divergenciju toplinskog kapaciteta te postojanje latentne topline što je snažna indikacija faznog prijelaza prvog reda. S druge strane, intenzitet drugog harmonika u optičkim mjerenjima i energijski procjep određen iz magnetske susceptibilnosti ispod 135 K slijede slično temperaturno ponašanje kao i parametar uređenja u BCS teoriji što bi pak upućivalo na fazni prijelaz drugog reda. Ovakvi kontradiktorni zaključci ukazuju na potrebu dodatnih eksperimentalnih i teorijskih rezultata ne bi li se riješila očito vrlo kompleksna priroda CO faznog prijelaza u alpha-(BEDT-TTF)2I3. Ovdje ćemo prikazati naše rezultate mjerenja dc otpornosti na monokristalima alpha-(BEDT-TTF)2I3 visoke kvalitete duž sva tri kristalografska smjera u temperaturnom području 30-300 K koji pokazuju odlike i faznog prijelaza prvog i faznog prijelaza drugog reda. Naime, otpornost duž sva tri smjera na 135 K pokazuje skok od oko tri reda veličine, a daljnjim snižavanjem temperature se jasno može prepoznati doprinos aktivacijskog ponašanja s odgovarajućim energijskim procjepom koji slijedi sličnu temperaturnu ovisnost kao i parametar uređenja u BCS teoriji. Dobivene rezultate ćemo diskutirati u odnosu na druge eksperimentalne činjenice i u svjetlu najnovijih DFT računa.

La1-xCaxMnO3 belongs to the family of manganese oxides, known as manganites, with a general chemical formula R1-xAxMnO3, where R is a rare earth element or Bi and A an alkali or alkaline earth metal or Pb. These compounds have been investigated since 1950., but a huge interest started in 1994. with the discovery of the famous colossal magnetoresistance (CMR). Besides CMR, manganites are interesting because of their very rich phase diagrams which show plenty of intriguing phenomena such as metal- insulator transition, charge ordering, multiferroicity, magnetocaloric effect, colossal thermoelectric power, phase coexistence, etc. In the case of the investigated compound La1-xCaxMnO3 the phase diagram consists of the three large parts: a paramagnetic (PM) insulating phase at high temperatures for all x, a ferromagnetic (FM) metallic ground state for 0.2 < x < 0.5 and an antiferromagnetic (AFM) charge order (CO) insulating ground state for 0.5 < x < 0.87. CMR effect is closely related to the FM phase and has maximum value at the Curie temperature. At present, it is believed that across the phase diagram there are areas where two phases can coexist, particularly close to the boundary between the two phases. Especially interesting is the coexistence between the FM metallic and CO/AFM insulating phase which is believed to be the key for understanding the CMR effect. Our recent work on magnetotransport properties of manganites thin films La1-xCaxMnO3 for x > 0.5 has shown the existence of CMR, FM and metal- insulator transition, properties characteristic for x < 0.5, which has been ascribed to the presence of FM clusters in the CO/AFM background. Here we present a continuation of this research to lower temperatures and higher magnetic fields which reveals a huge difference between field- and zero-field cooled resistivity curve and unusual time relaxation of the resistivity after application of an external magnetic field. We discuss this features in terms of the FM/AFM phase separation scenario.

Manganites La1-xCaxMnO3 belong to the family of manganese oxides with a general chemical formula R1-xAxMnO3, where R represents a rare earth element or Bi and A an alkali or alkaline earth metal or Pb. Replacement of trivalent R and divalent A introduces a mixed valence state Mn3+/Mn4+ and depending on the concentration x causes a presence of various phases in the phase diagrams of R1-xAxMnO3. A huge interest for this family of compounds started in 1994. when Jin et al. found a huge decrease of resistivity in external magnetic field close to Curie temperature known as colossal magnetoresistance (CMR). CMR is present in the part of the phase diagram with ferromagnetic metallic ground state which for the investigated system La1-xCaxMnO3 appears for concentrations 0.2 < x < 0.5. Here we focused on the poorly explored part of the phase diagram x > 0.5 with a paramagnetic insulating phase at high, charge order phase at intermediate and antiferromagnetic insulating phase at low temperatures. We performed magnetotransport and magnetization measurements in the temperature interval 4.2-300 K and magnetic fields up to 5 T on thin film manganites for different concentrations 0.52 ≤ x ≤ 0.75. Our results show traces of CMR and ferromagnetism and a strong coupling between magnetic and transport properties which can be interpreted in terms of spin dependent variable range hopping mechanism and a coexistence of ferromagnetic and antiferromagnetic phase.

alpha-(BEDT-TTF)2I3 pripada familiji spojeva temeljenoj na organskoj molekuli bis-(ethylene-dithio)-tetrathiafulvalene (BEDT-TTF) koja se u novije vrijeme intenzivno istražuje zbog nekonvencionalne supravodljivosti, uređenja naboja, elektronske feroelektričnosti, stanja kvantne spinske tekućine itd. Kao i ostali pripadnici ove familije, i alpha-(BEDT-TTF)2I3 ima slojevitu kristalnu strukturu koja uzrokuje kvazidvodimenzionalna elektronska svojstva. Pri atmosferskom tlaku alpha-(BEDT-TTF)2I3 na visokim temperaturama pokazuje polumetalna svojstva s malim džepovima elektrona i šupljina, a na temperaturi TCO = 136 K prelazi u stanje uređenja naboja (CO) s feroelektričnim oznakama. Primjena tlaka uzrokuje postepeno potiskivanje CO faznog prijelaza, a pri određenim uvjetima i pojavu supravodljive faze ispod 7 K. Mjerenja Hallovog efekta i magnetootpora pri tlakovima većim od 1.5 GPa, kada je CO faza u potpunosti potisnuta, pokazuju da se koncentracija slobodnih nosioca naboja od 300 K do 2 K smanjuje 6 redova veličine, dok njihova pokretljivost raste 6 redova veličine. Ovi rezultati pokazuju da je alpha-(BEDT-TTF)2I3 iznad 1.5 GPa poluvodič s nultim energijskim procjepom čiji se nosioci naboja ponašaju kao Diracovi fermioni što je u skladu s najnovijim proračunima vrpci. Budući da su zbog spomenutih izrazito zanimljivih fizikalnih svojstava magnetotransportna istraživanja u literaturi uglavnom provedena uz primjenu visokih tlakova, proveli smo mjerenja pri atmosferskom tlaku koja nedostaju: dc otpornost, anizotropija dc otpornosti, magnetootpor i Hallov efekt u temperaturnom intervalu 40-300 K i u magnetskim poljima do 5 T. Dobivene rezultate usporedit ćemo s rezultatima magnetotransportnih istraživanja alpha-(BEDT-TTF)2I3 pod tlakom kao i s našim rezultatima magnetotransportnih istraživanja srodnog spoja kappa-(BEDT-TTF)2Cu2(CN)3 u kojem CO faza ne postoji.

(TMTTF)2ReO4 i (TMTTF)2BF4 pripadaju u skupinu takozvanih Fabreovih soli koje pri sobnoj temperaturi većinski pokazuju kvazi 1D metalnu vodljivost. Variranjem raznih parametara poput tlaka, temperature te vrste aniona, dobiven je vrlo bogat fazni dijagram Fabreovih soli u kojem su neka od mogućih stanja: metalno stanje, stanje uređenja naboja, spin-Peierlsovo stanje, supravodljivo stanje i stanje vala gustoće spina[1]. Od prije je poznato da navedena dva spoja pri sobnoj temperaturi pokazuju kvazi 1D metalnu vodljivost te da spuštanjem temperature ispod 230 K za (TMTTF)2ReO4, odnosno 84 K za (TMTTF)2BF4, oba spoja prolaze kroz metal-izolatorski fazni prijelaz u izolatorsko stanje uređenja naboja. Također, oba spoja spadaju u skupinu soli s nesimetričnim anionima pa daljnjim spuštanjem temperature ispod 157 K za (TMTTF)2ReO4, odnosno 41.5 K za (TMTTF)2BF4, dolazi do zamrzavanja orijentacije aniona i loma simetrije pa oba spoja prolaze kroz izolator-izolatorski fazni prijelaz u stanje uređenja aniona[2]. U cilju boljeg razumijevanja transportnih mehanizama, mjerili smo otpornost i Hallov koeficijent RH u ovisnosti o temperaturi. Otpornost je mjerena u smjeru najveće vodljivosti, kao i RH (magnetsko polje je okomito na smjer struje) koji je mjeren AC kompenzacijskom metodom u magnetskim poljima do 9 T te za temperature 45 K< T < 300 K. Oba spoja pri sobnoj temperaturi imaju približno jednaku vrijednost RH koja je oko 3 puta veća od teorijski predviđene vrijednosti. RH je u oba spoja pozitivan što je u skladu s činjenicom da su nosioci naboja šupljine. Fazni prijelaz u stanje uređenja naboja posebno je naglašen u (TMTTF)2ReO4 gdje smo detektirali naglu promjenu predznaka RH u uskom intervalu temperatura. Daljnjim opadanjem temperature ispod faznog prijelaza u stanje uređenja naboja, porast RH u oba spoja prati eksponencijalni porast otpornosti što odgovara ponašanju izolatora kod kojih je ovakvo ponašanje posljedica smanjenja broja nosioca naboja sa snižavanjem temperature. Dobivene rezultate ćemo usporediti sa rezultatima srodnih spojeva te interpretirati u okviru postojećih teorijskih modela. [1] M. Dressel, Naturwissenschaften 94, 527 (2007). [2] B. Köhler, E. Rose, M. Dumm, G. Untereiner, and M. Dressel, Phys. Rev. B 84, 035124 (2011)

alpha-(BEDT-TTF)2I3 is a quasi-2D organic conductor most famous for its prominent charge order within molecular planes below TCO =136 K [1]. Due to the breaking of an inversion center, the response at the charge ordering transition should have a ferroelectric character [2, 3]. Puzzlingly, at the moment it is unclear whether the ferroelectric peak appears in the dielectric properties at all [4]. Furthermore, the low-lying excitations above the ground state seem to bring forth both a phason-like as well as a soliton-like relaxation, which have so far not been reported to appear together in similar systems [5]. In order to explore these open questions, we have carefully determined the direction-dependent (in-plane and out-of-plane) dielectric response in alpha-(BEDT-TTF)2I3 together with resistance and Hall effect measurements down to lowest temperatures. The temperature dependence of the Hall coefficient absolute value follows a similar behavior as the resistivity. An intriguing feature is found at TCO where the Hall coefficient changes sign. Another interesting property is a change in the in-plane transport activation energy around 60 K. On the other hand, dielectric measurements give strongly anisotropic and complex spectra. Our results are discussed within the wider context of strongly correlated systems with charge order. [1] T. Takahashi, Y. Nogami, and Kyuya Yakushi, J. Phys. Soc. Jpn. 75, 051008 (2006). [2] T. Kakiuchi, Y. Wakabayashi, H. Sawa, T. Takahashi, and T. Nakamura, J. Phys. Soc. Jpn. 76, 113702 (2007) [3] K. Yamamoto, A. A. Kowalska, and K. Yakushi, Appl. Phys. Lett. 96, 122901 (2010). [4] T. Ivek, B. Korin-Hamzić, O. Milat, S. Tomić, C. Clauss, N. Drichko, D. Schweitzer, and M. Dressel, Phys. Rev. Lett. 104, 206406 (2010) ; P. Monceau, private communication (2014). [5] T. Ivek, B. Korin-Hamzić, O. Milat, S. Tomić, C. Clauss, N. Drichko, D. Schweitzer, and M. Dressel, Phys. Rev. B 83, 165128 (2011).

Manganites La1-xCaxMnO3 belong to the family of manganese oxides with a general chemical formula R1- xAxMnO3, where R represents a rare earth element or Bi and A an alkali or alkaline earth metal or Pb. Replacement of trivalent R and divalent A introduces a mixed valence state Mn3+/Mn4+ and depending on the concentration x causes a presence of various phases in the phase diagrams of R1-xAxMnO3. A huge interest for this family of compounds started in 1994. when Jin et al. found a huge decrease of resistivity in external magnetic field close to Curie temperature known as colossal magnetoresistance (CMR). CMR is present in the part of the phase diagram with ferromagnetic metallic ground state which for the investigated system La1-xCaxMnO3 appears for concentrations 0.2 < x < 0.5. Here we focused on the poorly explored part of the phase diagram x > 0.5 [3] with a paramagnetic insulating phase at high, charge order phase at intermediate and antiferromagnetic insulating phase at low temperatures. We performed magnetotransport and magnetization measurements in the temperature interval 4.2-300 K and magnetic fields up to 5 T on thin film manganites for different concentrations 0.5 < x < 0.8. Our results show traces of CMR and ferromagnetism and a strong coupling between magnetic and transport properties which can be interpreted in terms of spin dependent variable range hopping mechanism and a coexistence of ferromagnetic and antiferromagnetic phase.

Upon cooling the highly anisotropic organic conductors (TMTTF) 2 X undergo transitions to various ordered states in the charge and spin degrees of freedom and therefore turn out to be an excellent choice for exploring the phenomena of low-dimensional physics. In order to study the transport mechanism of these quasi-one-dimensional (1D) organic salts, the temperature-dependent Hall effect of (TMTTF) 2 X (X=BF 4 , ReO 4 , AsF 6 , SbF 6 ) has been measured by an AC compensation technique with current injection along the high-conducting a-axis. At elevated temperatures the Hall coefficient R H of all investigated compounds seems to be constant, positive and somehow enhanced compared to the calculated value for one hole per unit cell. Beyond the charge order phase transition the Hall coefficient follows similar exponential laws as the resistivity data. This indicates the behavior of a semiconductor, where the change in ρ(T) mainly originates from the change in the number of carriers. Here we discuss how the Hall coefficient is influenced by anisotropy, localization effects, anion symmetry and charge- as well as anion-ordering phenomena at low temperatures. We compare the results to resistivity studies and theoretical expectations.

We have in detail characterized the anisotropic charge response of the dimer Mott insulator κ−(BEDT-TTF)2Cu2(CN)3 by dc conductivity, Hall effect, and dielectric spectroscopy. At room temperature, the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity ρ(T). Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K, we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also, the relaxation levels off. The observed behavior bears features of relaxorlike ferroelectricity. Because heterogeneities impede its long-range development, only a weak-tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition [1, 2]. Conversely, the dielectric response observed in dimer Mott insulator phases with no charge ordering [3] is rather intriguing [4, 5, 6, 7]. In this presentation we review our in-depth study (dc conductivity, Hall effect and dielectric spectroscopy) of the anisotropic charge response in an unconventional Mott insulator with spin liquid kappa-(BEDT-TTF)2Cu2(CN)3. Variable-range hopping transport within molecular planes in dc limit and an anomalously broad anisotropic dielectric relaxation in audio-frequency range demonstrate the inherent heterogeneity present in nominally pure single crystals of kappa-(BEDT-TTF)2Cu2(CN)3. The relaxation bears fingerprints of relaxor ferroelectricity: a gradual slowing down becomes dominated by tunneling at low temperatures and at the bifurcation temperature anomalous features in dielectric constant, mean relaxation time and spectral broadening are detected. We argue that the observed behavior is due to a strong charge-spin-lattice coupling reflecting the gradual emergence of random potential and domain structure originated in the anion network. [1] T.Ivek et al., Phys.Rev.B83, 165128 (2011). [2] T.Ivek et al., Phys.Rev.B86, 245125 (2012). [3] K.Sedlmeier et al., Phys.Rev.B86, 245103 (2012). [4] M.Abdel-Jawad et al., Phys.Rev.B82, 125119 (2010). [5] S.Iguchi et al., Phys.Rev.B87, 075107 (2013). [6] P.Lunkenheimer et al., Nat. Mater. 11, 755 (2012). [7] S.Tomic et al., J.Phys.: Condens.Matter 25, 436004 (2013). [8] M.Pinteric et al., to be submitted (2014).

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition [1, 2]. Conversely, the dielectric response observed in dimer Mott insulator phases with no charge ordering is rather intriguing [3, 4, 5]. In this presentation we review our recent results of anisotropic complex conductivity (dc – MHz) in the magnetic phase of kappa-(BEDT-TTF)2Cu[N(CN)2]Cl and in the spin-liquid phase of kappa-(BEDT-TTF)2Cu2(CN)3 [6, 7]. We discuss possible explanations for the observed dynamics and compare them with the well-known fingerprints of the charge/spin density wave response to ac electric fields. [1] T.Ivek et al., Phys.Rev.B83, 165128 (2011). [2] T.Ivek et al., Phys.Rev.B86, 245125 (2012). [3] M.Abdel-Jawad et al., Phys.Rev.B82, 125119 (2010). [4] S.Iguchi et al., Phys.Rev.B87, 075107 (2013). [5] P.Lunkenheimer et al., Nat. Mater. 11, 755 (2012). [6] S.Tomic et al., J.Phys.: Condens.Matter 25, 436004 (2013). [7] M.Pinteric et al., in preparation (2014).

Manganites La1-xCaxMnO3 belong to the family of manganese oxides with a general chemical formula R1-xAxMnO3, where R stands for a rare earth element and A for an alkali or alkaline earth metal. One of the most prominent property of manganese oxides is a huge decrease of resistivity in external magnetic field close to Curie temperature known as colossal magnetoresistance (CMR). In these systems CMR can be as large as -99%, unlike magnetoresistance of most materials which is usually small (a few percent). Except CMR, manganese oxides are interesting because of their very rich phase diagrams as a consequence of the fine interplay of charge, spin, lattice and orbital interactions. CMR is present in the part of the phase diagram of manganese oxides with ferromagnetic metallic ground state and in the case of the investigated system La1-xCaxMnO3 for concentrations 0.2 < x < 0.5. While pure LaMnO3 and CaMnO3 are antiferromagnetic insulators and contain Mn3+, Mn4+ respectively, doped manganites La1-xCaxMnO3 have a variety of different phases and contain both Mn3+ and Mn4+ (a mixed valence state). Here we focused on the poorly explored part of the phase diagram x > 0.5 with a paramagnetic insulating phase at high, charge order phase (CO) at intermediate and antiferromagnetic insulating phase at low temperatures. We performed magnetotransport measurements in the temperature interval 4.2-300 K and magnetic fields up to 5 T on a series of thin film manganites (170 nm thick) of different concentrations 0.5 < x < 0.8 obtained by metalorganic aerosol deposition technique. We will show and discuss the results of magnetotransport properties by which we investigated the influence of the concentration x on resistivity, CO phase transition temperature, magnetoresistance and anisotropy of magnetoresistance.

Oksidi mangana R1−xAxMnO3 (gdje R označava element rijetke zemlje, A alkalijske elemente) predstavljaju jedinstveno područje za istraživanje utjecaja elektronskih korelacija u materijalima koje se odnose na naboj, spin, orbitalne stupnjeve slobode i stupnjeve slobode rešetke budući da su prisutne interakcije usporedive jakosti što ima za posljedicu vrlo bogati fazni dijagram. Naša istraživanja odnose se na seriju filmova manganita La1-xCaxMnO3 različitih koncentracija (x = 0.52, x = 0.58 i x = 0.75). Dok je početni spoj LaMnO3 izolator (s osnovnim antiferomagnetskim stanjem) i sadrži Mn3+ kation, dopiranje dvovalentnim Ca2+ kationom uzrokuje pojavu Mn4+ kationa te time i stanje „mješanih valencija“ Mn3+/Mn4+, a kao posljedicu veliku promjenu u fizikalnim svojstvima. Jedno od najpoznatijih svojstava manganovih oksida je kolosalni magnetootpor (CMR) koji se pojavljuje u La1-xCaxMnO3 za x ≈ 0.3 (veliko smanjenje otpornosti u vanjskom magnetskom polju u blizini Curieve temperature). Kako su do sada istraživanja uglavnom bila ograničena na koncentracije x < 0.5, a o prirodi samog spoja i pogotovo CMR još uvijek postoji čitav niz nepoznanica fokusirali smo se na koncentracije x > 0.5 gdje fazni dijagram karakterizira paramagnetsko stanje na visokim temperaturama, te sa snižavanjem temperature fazni prijelazi u stanje uređenja naboja (CO) i antiferomagnetsko stanje (AF). Mjerenja otpornosti, ovisnosti magnetootpornosti o temperaturi, jačini i smjeru vanjskog magnetskog polja te Hallovog efekta provedena su u širokom području temperatura 30 K < T < 300 K i u magnetskim poljima do 5 tesla. Prikazati ćemo i diskutirati rezultate mjerenja pomoću kojih smo odredili temperaturu faznog prijelaza u CO stanje za sve x, promjene u otpornosti u ovisnosti o x, promjene doprinosa CMR u ovisnosti o x, vrstu nosioca naboja na visokim temperaturama te promjenu predznaka Hallovog koeficijenta ispod TCO.

Mottov izolator kappa-(BEDT-TTF)2Cu2(CN)3 se sastoji od 2D slojeva molekulskih dimera raspoređenih u trokutastu rešetku. Usprkos jakom antiferomagnetskom vezanju J ~ 250 K, NMR mjerenja su pokazala da nema dugodosežnog magnetskog uređenja do 32 mK što ukazuje da je osnovno stanje sistema spinska tekućina. Optička vodljivost slijedi zakon potencija u terahertz području prividno u skladu s teorijskim očekivanjima za doprinos spinonskih pobuđenja unutar nabojskog procjepa, a uslijed vezanja na unutarnje baždarno polje. Međutim, eksponent je puno manji od teorijskog. Neki pak drugi teorijski modeli sugeriraju postojanje kvantnih električnih dipola koji su u drugom redu povezani sa spinom i vode na realizaciju dipolarno-spinske tekućine. Ujedno je sugerirano da su fluktuacije tih dipola u ishodištu dielektričnog odgovora. Unatoč velikom broju rezultata, mehanizam i porijeklo pobuđenja naboja su još uvijek nejasni. U ovom radu ćemo opisati i diskutirati rezultate naših galvanomagnetskih mjerenja te mjerenja dc otpornosti i dielektrične spektroskopije duž sva tri kristalografska smjera koji bacaju novo svjetlo na ovaj iznimno intrigantan fizikalni sistem.

Hallov koeficijent RH je bitna fizikalna veličina za karakterizaciju materijala, budući da odražava strukturu vrpce, koncentraciju i predznak nosioca naboja. U jako koreliranim sustavima RH pokazuje kompleksnu ovisnost o raznim parametrima (temperatura, magnetsko polje, dimenzionalnost sustava...). U slučaju reducirane dimenzionalnosti (visoko-anizotropni sustavi), elektronske korelacije postaju još istaknutije, što se jasno pokazuje i u Hallovom efektu. Za izotropne sustave mjerenja Hallovog efekta provode se u standardnoj geometriji, dok je u slučaju visoko-anizotropnih sustava nužan uvjet za dobivanje kvalitetnih i pouzdanih rezultata korištenje adekvatne geometrije mjerenja. U tu svrhu nužno je koristiti koncept ekvivalentnog izotropnog uzorka (EIS) [1]. Ovaj smo pristup detaljno primijenili pri mjerenjima Hallovog efekta kvazi-jednodimenzionalnog organskog vodiča TTF-TCNQ, za koji u literaturi postoje samo dva rezultata iz 1977. g., dobivena u ograničenom intervalu visokih temperatura, a koji se međusobno razlikuju i u iznosu i u predznaku [2] [3]. Kristalnu strukturu spoja TTF-TCNQ karakteriziraju odvojeni lanci u koje se slažu planarne TTF i TCNQ molekule. Uslijed prijenosa naboja s molekule TTF (kation) na TCNQ (anion) oba tipa lanca pokazuju metalno ponašanje: u TTF lancu nosioci naboja su šupljine, a u TCNQ lancu elektroni. Direktna posljedica ovakve strukture je izrazita anizotropija vodljivosti: σb>σc>σa pri čemu je σb/σc ≈ 102, σb/σa ≈ 103. Dok je na visokim temperaturama vodljivost za sva tri kristalografska smjera metalnog tipa, ispod 60K dolazi do serije faznih prijelaza te materijal postepeno prelazi u stanje izolatora. Mjerenja Hallovog efekta provedena su u širokom području temperatura 30K

The only published Hall effect measurements of TTF-TCNQ date back to 1977. They were performed in the high temperature metallic region above the phase transitions, and the results vary in their sign and values. The aim of the present work has been to extend the previous investigations to lower temperatures and higher magnetic fields and to compare the new data with the known results.

Proučavanje fizikalnih svojstava sistema sa jakim interakcijama posebno je važno u slučaju reducirane dimenzionalnosti gdje elektronske korelacije postaju još istaknutije. Vrlo osjetljiv odnos između elektronskih i strukturnih svojstava omogućuje da se modifikacijom strukturnih svojstava mijenja i anizotropija sistema. Istraživanje magnetotransportnih svojstava (anizotropije otpornosti, Hallovog efekta, magnetootpora) pokazuje se kao važno sredstvo za istraživanja fundamentalnih svojstava kao što su karakter vodljivosti, elektronske korelacije, stupanj dimenzionalnosti (od strogo 1D do 3D), fenomeni uređenja, fazni prijelazi, ... U tom smislu ova istraživanja obuhvaćaju organske vodiče (TMTSF)2ReO4 i (TMTTF)2AsF6, gdje je ustanovljen prijelaz u strogo 1D režim [1] ; kvazi-1D kuprate Sr14−xCaxCu24O41 (0

The future developments of new spintronic devices require high mobility 2DEG to inject and manipulate spins. Recently, such high mobility electron gas has been reported in the LaAlO_3/SrTiO_3 system and attributed to charge transfer at the polar interface. Such oxide based 2DEG is promising since it could be combined with other oxide materials taking advantage of their attractive versatility and multifunctional character. In this charge transfer mechanism the carrier concentration is very high, about 10^21 cm^(-3) and presents a moderate mobility compared to doped SrTiO3 single crystal. An alternative way to obtain high mobility electron gas while controlling the carrier concentration and its extension is by ion etching. We will present analysis of the distribution of defects and mobile carriers generated by means of preferential ion-beam etching of SrTiO_3 single crystals by combining positron annihilation spectroscopy (PAS), conductive-tip atomic force microscopy (CT-AFM) and low temperature magnetotransport. We demonstrate that vacancies generated at the surface by room-temperature ion irradiation diffuse on the micron scale and that consequently, carriers are distributed on the same scale.

We present Hall effect measurements of two-leg ladder Sr14-xCaxCu24O41 (0 10). They are the first superconducting copper oxides (superconductivity occurs under pressure for x>10) without the CuO2 planes, characteristic for high-temperature superconductors. The question of charge dynamics and hole distribution between the ladders and chains is still open. Our Hall effect results show typical semiconducting behavior for x

Istraživali smo magnetotransportna svojstva (anizotropiju otpornosti, Hallov efekt i magnetootpor) za tri skupine sistema s različitim stupnjem anizotropije: organske (supra)- vodiče (TMTSF)2ReO4 i (TMTTF)2AsF6, kvazi-jednodimenzionalne kuprate sastava Sr14-xCaxCu24O41 (0 1D prijelaz unutar unifciranog faznog dijagrama, kako prelazimo iz (TMTSF)2X serije u (TMTTF)2X seriju. Osim toga smo dobili dodatne informacije o prijelazu uredenja naboja u (TMTTF)2AsF6 i prijelazu anionskog uredenja u (TMTSF)2ReO4. Za kvazi-1D kuprate smo ustanovili da je vrlo mala promjena u broju nosioca naboja na ljestvicama odgovorna za značajnu promjenu u otpornosti (od izolatorske do metalne) kako se povečava udio Ca. Uz to se za sastav x = 11.5 opaža kvalitativna sličnost s dvodimenzionalnim supravodljivim kupratima, unatoč tome što je unutar ravnina ljestvica prisutna značajna anizotropija za razliku od gotovo izotropnih CuO2 ravnina. U slučaju heterostruktura smo pokazali da se sloj s velikom pokretljivošću elektrona proteže duboko u SrTiO3 substrat, dokazali da je taj sloj trodimenzionalan i objasnili da prilikom rasta tankog filma LaAlO3 nastaju kisikove vakancije, koje djeluju kao donor vrlo pokretljivih elektrona i procesom difuzije dospijevaju duboko u substrat.

Ohtomo i Hwang (Nature, 427 (2004) 423) su na 6 nm tankom filmu LaAlO3 (LAO) naparenom na SrTiO3 (STO) opazili metalno ponašanje i pokretljivosti veće od 10^4 cm2/Vs. Ta svojstva bila su pripisana 2D elektronskom plinu oformljenom na granici STO i LAO, što može biti od posebnog interesa za razvoj spintroničkih elemenata (npr. Datta-Das spin-FET). Naša magnetotransportna mjerenja (T > 300 mK, B < 18 T) [1] su pokazala da se ipak radi o 3D strukturi, što smo kasnije i direktno potvrdili inovativnim korištenjem CT-AFM eksp. tehnike. Navedena svojstva posljedica su dopiranja supstrata STO šupljinama kisika za vrijeme rasta tankog filma LAO, te je pokazano da je debljina vodljivog sloja reda veličine čak nekoliko stotina μ m. Diskutirat ćemo i nove načine realizacije i karakterizacije visokopokretljivog elektronskog sloja u monokristalu STO. [1] M.Basletić, J.-L.Maurice, C.Carretero, G.Herranz, O.Copie, M.Bibes, E.Jacquet, K.Bouzehouane, S.Fusil, A.Barthelemy, Nature Mater. 7 (2008) 621 ; G.Herranz, M.Basletić, M.Bibes, C.Carrétéro, E.Tafra, E.Jacquet, K.Bouzehouane, C.Deranlot, A.Hamzić, J.-M.Broto, A.Barthélémy, A.Fert, Phys. Rev. Lett. 98 (2007) 216803

We present Hall-effect measurements of two-leg ladder compounds Sr14− xCaxCu24O41 (0

La recherche portant sur les semiconducteurs magnétiques est d’ une grande importance pour l’ électronique de spin. Récemment des expériences ont aussi suggéré l’ existence de ferromagnétisme dans La_0.5Sr_0.5Ti_O_(3-delta) dopé avec du cobalt. Contrairement a d’ autres systemes dilués, celui-ci présente l’ originalité d’ avoir comme matrice hôte un métal fortement corrélé et non semiconducteurs, ce qui est susceptible de donner lieu a des mécanismes d’ échange de nature différente. Nous avons suivi cette approche en dopant SrTiO_3, préalablement dopé avec du lanthane, avec l.5% de cobalt (Co-LSTO). Les échantillons ont été fabriqués par ablation laser pulsé avec un laser Nd:YAG. Dans le but de comprendre l’ origine des propriétés magnétiques de Co-LSTO, nous avons procédé a une large étude structurale, ainsi qu’ a la mesure d’ une polarisation en spin pour des jonctions tunnels avec des électrodes de Co-LSTO et nous avons trouvé que les conditions de croissance, comme la pression partielle d’ oxyg&egrave ; ; ne, ont une influence importante sur les propriétés magnétiques, révélant le rôle des défauts (lacunes d’ oxygene, p.ex.) Pour mesurer la polarisation en spin du matériau, des jonctions tunnels &agrave ; ; base de Co-LSTO ont été fabriquées par lithographie optique. La mesure de la magnétorésistance tunnel TMR pour des jonction Co-LSTO/LAO/Co donne des valeurs de TMR de l’ ordre de 20% ce qui nous permettent de déduire une polarisation en spin pour Co-LSTO de l’ ordre de 80%. Les expériences de spectroscopie d’ absorption de rayon X et de dichro&iuml ; ; sme circulaire magnétique nous ont permis de sonder les états électroniques des atomes de cobalt et de titane, important pour comprendre les origines microscopique des propriétés magnétiques nos films de Co-LSTO. En particulier, les signatures spectrales du XAS et de l’ XMCD indiquent que le cobalt est dans un état ionique, coexistant dans certains cas avec du Co métallique. Au vu de l’ ensemble de ces résultats, nous tenterons de dégager des conclusions quant a la nature du ferromagnétisme observé dans les couches minces de Co-LSTO.