Single crystals of DPPH grown from diethyl ether and carbon disulfide solutions - Crystal structures, IR, EPR and magnetization studies

Single crystals of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) obtained from diethyl ether (ether) and carbon disulfide (CS2) were characterized by the X-ray diffraction, IR, EPR and SQUID magnetization techniques. The X-ray structural analysis and IR spectra showed that the DPPH form crystallized from ether (DPPH1) is solvent free, whereas that one obtained from CS2 (DPPH2) is a solvate of the composition 4DPPH.CS2. Principal values of the g-tensor were estimated by the X-band EPR spectroscopy at room and low (10 K) temperatures. Magnetization studies revealed the presence of antiferromagnetically coupled dimers in both types of crystals. However, the way of dimerization as well as the strength of exchange couplings are different in the two DPPH samples, which is in accord with their crystal structures. The obtained results improved parameters accuracy and enabled better understanding of properties of DPPH as a standard sample in the EPR spectrometry

Model paramagnetske probe u feroelektričima s vodikovim vezanjem

The modified strong dipole-proton coupling model and Monte Carlo calculation are employed to describe paramagnetic defect in hydrogen bonded ferroelectric. In this model, probe is treated as ``soft" dipole impurity in the system with N = 108 dipoles. The effective double-well type potential of the probe is obtained and its temperature dependence in the paraelectric phase is studied. It is shown that the experimentally detected activation energy of the polarization fluctuation of the SeO43- probe can be related to the effective activation energy. The model is compared with the earlier proposed local ``pseudo freeze-out" model which exhibits larger deviation from the experimental results than the suggested modified strong dipole-proton coupling model.Primijenili smo izmijenjeni model jakog vezanja i Monte Carlo račun za opis paramagnetskog defekta vodikom-vezanog feroelektika. U ovom se modelu proba uzima kao “meka” diolna nečistoća u sustavu N = 108 dipola. Izvodi se efektivan potencijal tipa dvojne jame i proučava njegova temperaturna ovisnost u paraelektričnoj fazi. Pokazuje se kako se eksperimentalno opažena aktivacijska energija polarizacijske fluktuacije probe SeO3− 4 može povezati s efektivnom aktivacijskom energijom. Ovaj se model uspoređuje s ranije predloženim modelom lokalnog “pseudo zamrzavanja” koji pokazuje veća odstupanja od eksperimentalnih podataka nego predloženi izmijenjen model jakog vezanja dipol-proton

An EPR methodology for measuring the London penetration depth for the ceramic superconductors

The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T(sub c) superconductors. The method utilizes the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T(sub c) is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, Neutron scattering, and magnetic susceptibility

Model paramagnetske probe u feroelektričima s vodikovim vezanjem

The modified strong dipole-proton coupling model and Monte Carlo calculation are employed to describe paramagnetic defect in hydrogen bonded ferroelectric. In this model, probe is treated as ``soft" dipole impurity in the system with N = 108 dipoles. The effective double-well type potential of the probe is obtained and its temperature dependence in the paraelectric phase is studied. It is shown that the experimentally detected activation energy of the polarization fluctuation of the SeO43- probe can be related to the effective activation energy. The model is compared with the earlier proposed local ``pseudo freeze-out" model which exhibits larger deviation from the experimental results than the suggested modified strong dipole-proton coupling model.Primijenili smo izmijenjeni model jakog vezanja i Monte Carlo račun za opis paramagnetskog defekta vodikom-vezanog feroelektika. U ovom se modelu proba uzima kao “meka” diolna nečistoća u sustavu N = 108 dipola. Izvodi se efektivan potencijal tipa dvojne jame i proučava njegova temperaturna ovisnost u paraelektričnoj fazi. Pokazuje se kako se eksperimentalno opažena aktivacijska energija polarizacijske fluktuacije probe SeO3− 4 može povezati s efektivnom aktivacijskom energijom. Ovaj se model uspoređuje s ranije predloženim modelom lokalnog “pseudo zamrzavanja” koji pokazuje veća odstupanja od eksperimentalnih podataka nego predloženi izmijenjen model jakog vezanja dipol-proton

Study of the local field distribution on a single-molecule magnet-by a single paramagnetic crystal; a DPPH crystal on the surface of an Mn12-acetate crystal

The local magnetic field distribution on the subsurface of a single-molecule magnet crystal, SMM, above blocking temperature (T >> Tb) detected for a very short time interval (~ 10-10 s), has been investigated. Electron Paramagnetic Resonance (EPR) spectroscopy using a local paramagnetic probe was employed as a simple alternative detection method. An SMM crystal of [Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O (Mn12-acetate) and a crystal of 2,2- diphenyl-1-picrylhydrazyl (DPPH) as the paramagnetic probe were chosen for this study. The EPR spectra of DPPH deposited on Mn12-acetate show additional broadening and shifting in the magnetic field in comparison to the spectra of the DPPH in the absence of the SMM crystal. The additional broadening of the DPPH linewidth was considered in terms of the two dominant electron spin interactions (dipolar and exchange) and the local magnetic field distribution on the crystal surface. The temperature dependence of the linewidth of the Gaussian distribution of local fields at the SMM surface was extrapolated for the low temperature interval (70-5 K)

The Marić Hillfort Settlement near Mikleuška during the Late Bronze and the Early Iron Age

Prostor Moslavine, smješten na jugozapadnom dijelu kontinentalne Hrvatske, obuhvaća tranzicijski geografski položaj koji spaja sjeverozapadnu Hrvatsku s prostorom Slavonije na istoku te Posavinom na jugu. Ipak, do danas je ovo područje nedovoljno istraženo s tek malim brojem nalazišta koja se mogu pripisati kasnom brončanom i starijem željeznom dobu. Istraživanja na gradini Marić pokraj Kutine te kronološko-tipološka analiza keramičkih nalaza pokazala su da je naselje živjelo najvećim intenzitetom tijekom mlađe faze kasnoga brončanog doba te tijekom prijelaza na starije željezno doba. Pitanja koja se tiču ranijih faza naseljavanja na gradini ostaju otvorena. Kulturni utjecaji koji se mogu pratiti tijekom mlađe faze kulture polja sa žarama povezuju naselje na gradini s istovremenim nalazištima na prostoru Podravine i Posavine. Jednako tako, određeni nalazi upućuju na lokalne posebnosti koje nisu vezane samo uz prostor Moslavine nego i uz prostor sjeverozapadne Hrvatske. Malen broj nalaza upućuje na nastavak života na gradini tijekom starijega željeznog doba, no potpuniji prikaz toga razdoblja još uvijek nije moguće dati.The Moslavina region, situated in the south-western part of continental Croatia, occupies a transitional geographical position connecting the north-western parts of the country with Slavonia and Posavina regions. To this day it remains an insufficiently researched area with only a few known sites that can be attributed to the periods of the Late Bronze and the Early Iron Age. The research and pottery analysis have shown that the settlement on Marić hillfort near Kutina lived most intensely during the later phases of the Urnfield Culture and during the transitional period to the Early Iron Age. Questions regarding earlier setllement stages still remain open. Cutural influences that can be traced during the Late Urnfield Culture link the settlement on the hillfort with contemporary sites in the Podravina and Posavina regions. Some of the finds point out to local distinctions that are not only specific to Moslavina region, but to the area of north-western Croatia, as well. A small number of finds indicates that life on the hillfort continued into the Early Iron Age, but conclusions about a more complete picture of this period cannot be made

Microwave (EPR) measurements of the penetration depth measurements of high-Tc superconductors

The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T sub c superconductors. The method uses the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T sub c is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, neutron scattering, and magnetic susceptibility

Magnetic anisotropy of spin tetramer system SeCuO3_3 studied by torque magnetometry and ESR spectroscopy

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in SeCuO$_3$. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.Comment: 14 pages, 13 figure

The Marić Hillfort Settlement near Mikleuška during the Late Bronze and the Early Iron Age

Prostor Moslavine, smješten na jugozapadnom dijelu kontinentalne Hrvatske, obuhvaća tranzicijski geografski položaj koji spaja sjeverozapadnu Hrvatsku s prostorom Slavonije na istoku te Posavinom na jugu. Ipak, do danas je ovo područje nedovoljno istraženo s tek malim brojem nalazišta koja se mogu pripisati kasnom brončanom i starijem željeznom dobu. Istraživanja na gradini Marić pokraj Kutine te kronološko-tipološka analiza keramičkih nalaza pokazala su da je naselje živjelo najvećim intenzitetom tijekom mlađe faze kasnoga brončanog doba te tijekom prijelaza na starije željezno doba. Pitanja koja se tiču ranijih faza naseljavanja na gradini ostaju otvorena. Kulturni utjecaji koji se mogu pratiti tijekom mlađe faze kulture polja sa žarama povezuju naselje na gradini s istovremenim nalazištima na prostoru Podravine i Posavine. Jednako tako, određeni nalazi upućuju na lokalne posebnosti koje nisu vezane samo uz prostor Moslavine nego i uz prostor sjeverozapadne Hrvatske. Malen broj nalaza upućuje na nastavak života na gradini tijekom starijega željeznog doba, no potpuniji prikaz toga razdoblja još uvijek nije moguće dati.The Moslavina region, situated in the south-western part of continental Croatia, occupies a transitional geographical position connecting the north-western parts of the country with Slavonia and Posavina regions. To this day it remains an insufficiently researched area with only a few known sites that can be attributed to the periods of the Late Bronze and the Early Iron Age. The research and pottery analysis have shown that the settlement on Marić hillfort near Kutina lived most intensely during the later phases of the Urnfield Culture and during the transitional period to the Early Iron Age. Questions regarding earlier setllement stages still remain open. Cutural influences that can be traced during the Late Urnfield Culture link the settlement on the hillfort with contemporary sites in the Podravina and Posavina regions. Some of the finds point out to local distinctions that are not only specific to Moslavina region, but to the area of north-western Croatia, as well. A small number of finds indicates that life on the hillfort continued into the Early Iron Age, but conclusions about a more complete picture of this period cannot be made