Chirality and Magnetocaloricity in GdFeTeO6 as Compared to GdGaTeO6

GdFeTeO6 and GdGaTeO6 have been prepared and their structures refined by the Rietveld method. Both are superstructures of the rosiaite type (space group ). Their thermodynamic properties have been investigated by means of magnetization M and specific heat Cp measurements, evidencing the formation of the long-range antiferromagnetic order at TN = 2.4 K in the former compound and paramagnetic behavior down to 2 K in the latter compound. Large magnetocaloric effect allows considering GdFeTeO6 for the magnetic refrigeration at liquid hydrogen stage. Density functional theory calculations produce estimations of leading Gd–Gd, Gd–Fe and Fe–Fe interactions suggesting unique chiral 120° magnetic structure of Fe3+ (S = 5/2) moments and Gd3+ (J = 7/2) moments rotating in opposite directions (clockwise/anticlockwise) within weakly coupled layers of the rosiaite type crystal structure.

Static magnetic susceptibility in finite-density $$SU\left( 2\right) $$ lattice gauge theory

We study static magnetic susceptibility $$\chi (T, \mu )$$ χ ( T , μ ) in SU(2) lattice gauge theory with $$N_f = 2$$ N f = 2 light flavours of dynamical fermions at finite chemical potential $$\mu $$ μ . Using linear response theory we find that SU(2) gauge theory exhibits paramagnetic behavior in both the high-temperature deconfined regime and the low-temperature confining regime. Paramagnetic response becomes stronger at higher temperatures and larger values of the chemical potential. For our range of temperatures $$0.727 \le T/T_c \le 2.67$$ 0.727 ≤ T / T c ≤ 2.67 , the first coefficient of the expansion of $$\chi \left( T, \mu \right) $$ χ T , μ in even powers of $$\mu /T$$ μ / T around $$\mu =0$$ μ = 0 is close to that of free quarks and lies in the range $$(2, \ldots , 5) \cdot 10^{-3}$$ ( 2 , … , 5 ) · 10 - 3 . The strongest paramagnetic response is found in the diquark condensation phase at $$\mu >m\pi /2$$ μ > m π / 2 .

Un estudio de las propiedades estructurales, magnéticas y eléctricas de los compuestos Ba1-xNaxCoO3(x = 0.25, 0.5, 0.75)

Cobaltite-like materials having metal-insulator transitions are relevant in the consumer electronics market. In this work, we present the structural, magnetic, and electrical properties of Ba1-xNaxCoO3 (with x= 0.25, 0.5, 0.75) cobaltite. All samples were synthesized using a solid-state reaction process. Their crystal structure was determined using X-ray diffraction (XRD) data by the Rietveld method, which showed that all the samples were crystallized in the orthorhombic space group C2221 (N.° 20). The microstructure of the sintered samples was characterized by scanning electron microscopy (SEM). The magnetic susceptibility measurements confirmed a paramagnetic behavior for x≥ 0.5 in the temperature range that was used. Likewise, a broad peak around 33 K in the sample x = 0.25, and characteristic of antiferromagnetic behaviors were observed. On the other hand, resistivity contributed to determining the insulating behavior of samples where x = 0.5 and x = 0.75. In contrast, at low sodium content (x = 0.25), a metal-insulator transition was observed with transition temperature near 105 K.

Structural and Magnetic Properties of Potassium-Doped 2,3-DiMethylnaphthalene

The development of potential magnetic materials in metal-doped polycyclic aromatic hydrocarbons has been a research hotspot in recent years. Here we have successfully synthesized stable potassium-doped 2,3-dimethylnaphthalene samples. The combination of first-principles calculations and XRD results identifies that doping of potassium into 2,3-dimethylnaphthalene forms a monoclinic structure with a molar ratio of 1:2 between potassium and molecule. The red shifts in the Raman spectra indicate that potassium 4s electrons are transferred to the organic molecules. The magnetic measurements show that the doped materials exhibit a temperature-independent magnetization in the temperature region of 1.8–300 K, which is consistent with the Pauli paramagnetic behavior. This is distinct from the diamagnetism of pristine material. Compared to the previous focus on benzene ring structure, our study of aromatic hydrocarbon derivatives of benzene ring opens a new route for the development of this field.

Reduced- or ilmenite-type granites versus oxidized- or magnetite-type granites: occurrence in Iberian Variscan Belt

<p>The magnetic susceptibility (K<sub>m</sub>) of granites is an important characteristic and it is mainly controlled by the presence of certain oxide minerals like magnetite and/or ilmenite, as well as ferromagnesian phyllosilicates such as biotite. The abundance of magnetite or ilmenite can be explained by different redox conditions in the magma chamber and distinct magma sources. The presence of magnetite or ilmenite as accessory minerals represents oxidized- or magnetite-type granites and reduced- or ilmenite-type granites, respectively.</p><p>This work focuses on the K<sub>m</sub> of 20 Variscan granitic massifs from northern and central Portugal and considers the results obtained in about 750 sampling sites, in order to deduce the redox conditions in the magma system. These granites are essentially two mica mesocrustal and biotite-rich basicrustal/infracrustal in origin and their emplacement was related to Variscan orogeny. In the northern and central Portugal, three main ductile deformation Variscan phases were recognized and described: D<sub>1</sub>, D<sub>2</sub> and D<sub>3</sub>. The studied granites were subdivided in three main groups according to U-Pb dating, field observations and emplacement relative to the D<sub>3 </sub>phase. Therefore, the studied granites are subdivided as following: (1) syn-D<sub>3</sub> two-mica (mosc=biot) granites, ca. 311 Ma; (2) late-D<sub>3</sub> monzogranites, biotite-rich and two-mica granites (biot>mosc), ca. 300 Ma; (3) post-D<sub>3</sub> monzogranites and biotite-rich granites, < 299 Ma.</p><p>The evaluation of the K<sub>m</sub> variation of the different granite groups shows that, as granites become progressively younger, the K<sub>m</sub> parameter tends to increase as a result of the increasing in the mantellic contribution to the genesis of the magmas. Syn-D<sub>3</sub> granites display K<sub>m</sub> between 17.8 μSI and 186 μSI. This variation is due to the high textural and compositional diversity, including two-mica granites with different relative proportions of muscovite and biotite. Late-D<sub>3</sub> granites are represented by two-mica and biotite-rich granites with calcium plagioclase, with several degrees of post-magmatic alteration, implying iron leaching processes. These processes also promote the crystallization of secondary muscovite, which implied a decrease in the K<sub>m</sub> values, and also a wide dispersion of K<sub>m</sub> values ranging between 7.3 μSI and 276 μSI. Post-D<sub>3</sub> granites are mostly represented by biotite-rich granites with calcium plagioclase close to I-type granites. This granite group is divided into two subgroups: (i) post-D<sub>3</sub> ilmenite-type granites with K<sub>m</sub> values of ca. 113 μSI, typical of biotite-rich granites; and (ii) post-D<sub>3</sub> magnetite-type granites with K<sub>m</sub> values between 2078 μSI and 11676 μSI representing magnetite-type granites. In N and Central Portugal, these magnetite-type granites can occur in homogeneous plutons or in composite plutons constituted by ferromagnetic and paramagnetic facies.</p><p>As a conclusion, mostly of the granites from northern and central Portugal exhibit average K<sub>m</sub> values below 1000 μSI and are characterized by a paramagnetic behavior corresponding to reduced- or ilmenite-type granites. Among the all studied granites, only one pluton showed to be a truly oxidized- or magnetite-type granite, with K<sub>m</sub> of the order of 11676 μSI.</p><p><strong>Acknowledgements: </strong>This work was funded by the Fundação para a Ciência e a Tecnologia (FCT) under UIDB/04683/2020 project.</p>

The rock magnetism and biochronology of boundary events across the Cretaceous-Paleogene transition in Slovakia.

<p>Western Carpathians transitional sequence of Upper Cretaceous (e.g. Gosau Group) and Paleogene (e.g. Myjava-Hričov Group) sediments provide good premise for studying the Cretaceous-Paleogene boundary (K-Pg) as well as other end-Cretaceous to Middle Eocene events. In Slovakia, the Late Cretaceous formations of Gosau localities can be found in Brezovské Karpaty Mts, Myjava Upland and Mid Váh Valley. To gain insights to local changes in global cataclysm event, a combined study of planktonic bioevents and magnetic properties across K-Pg was studied in two Western Carpathians drilled sections, Žilina (Mid-Váh Valley region) and Kršteňany (Upper Nitra Depression).</p><p>The Žilina-Hradisko drill core (ZA-1) is 75 m long and overturned in position. The micropaleontological research of the ZA-1 drill core provides a stratigraphic data ranging from the Late Maastrichtian to Early Ypressian. The ZA-1 sequence reveals distinct changes in magnetic properties and bioproductivity, particularly at the K-Pg. Although most of the drilled sequence displays paramagnetic behavior and low remanent magnetization (average magnetic susceptibility 142μSI and NRM <1mA/m, respectively), at the K-Pg and during first half of Danian – up to base of P2 biozone, markedly higher magnetic susceptibility (MS) and NRM values were observed. This change could mostly be attributed to increased concentration of magnetic fraction and probably illustrates the paleoenvironmental changes as a result of the K-Pg event. The K-Pg interval is also marked by the presence of increased amount of superparamagnetic particles. A mixture of low and high coercivity minerals were detected throughout the drill core, with S-ratio varying between 0.2-0.9 (at K-Pg 0.6-0.9). An additional study of mercury (Hg) content, in combination with total organic carbon (TOC), of ZA-1 samples, reveals a short time enhanced (Hg/TOC >100ppb/wt%), possibly volcanogenic, Hg input during Late Maastrichtian 40cm below K-Pg and later in the second half of P1 biozone in Danian, but seems to indicate either weak or no correlation with magnetic properties. The Kršteňany section consists of two boreholes, KRS-1 and KRS-3, and comprises Late Cretaceous – Middle Eocene formations. Similarly to ZA-1, most of the KRS-3 displays paramagnetic behavior (MS <300μSI) and low NRM (<2mA/m). However, contrary to ZA-1, the distinct changes in magnetic properties at K-Pg interval were not observed. The Maastrichtian portion of KRS-3 displays elevated, but decreasing towards K-Pg, MS values due to considerable weathering and increased hematite and/or goethite content in red-bed formation in the bottommost part of the core. Paleocene sequence through middle Ypresian shows lowest MS with higher (in pelagic sequences) and lower (in siliciclastic sequences) MS zones, probably following transgressive-regressive cycles.</p><p>The research was supported by Czech Science Foundation project no. 19-07516S and by VEGA agency no 2/0013/20, and is in accordance with research plan no. RVO67985831.</p>

Synthesis of Spinel Nanocrystalline ZnFe2O4: Structural, Optical, Magnetic and Electrical properties.

The present paper deals with the synthesis of Zinc Ferrite (ZnFe2O4) nanoparticles using simple, low cost co - precipitation method and study the structural, optical, magnetic and electrical properties. The samples have been prepared at two different calcination temperatures of 400˚ C and 600˚ C. The XRD studies indicate that the synthesized ZnFe2O4 samples exhibit cubic spinel structure and that the grain size increases with calcination temperature. The FTIR spectra demonstrate bands associated with metal – oxygen bonds in the tetrahedral and octahedral sites. Moreover, no unwanted impurity such as nitrate has been detected in the synthesized samples revealing their high purity. The micro structural analysis shows that though most particles are irregular granular ones, some are spherical. The optical band gap energy is found to increase with increasing calcination temperature. The Vibrating Sample Magnetometer (VSM) studies reveal the super paramagnetic behavior of the synthesized samples, even for a high Fe: Zn ratio of 1:2. The electrical resistivity of the samples decreases with increase in calcination temperature.This phenomenon has been explained on the basis of the Verwey-de Boer mechanism.

Study of gadolinium substitution effects in hexagonal yttrium manganite YMnO3

In the present work, gadolinium substitution effects on the properties of yttrium manganite YxGd1−xMn0.97Fe0.03O3 (x from 0 to 1 with a step of 0.2) synthesized by an aqueous sol–gel method have been investigated. Partial substitution of Mn3+ by 57Fe3+ in the manganite was also performed in order to investigate deeper the structural properties of synthesized compounds applying Mössbauer spectroscopy. It was demonstrated that substitution of Y3+ by Gd3+ ions leads to the changes of structural, magnetic and morphological properties of investigated system. The crystal structure gradually transformed from hexagonal to orthorhombic with an increase of Gd3+ content in the crystal lattice. The mixed phase was obtained when x = 0.6, whereas other compounds were determined to be monophasic. Magnetization measurements revealed paramagnetic behavior of all specimens, however magnetization values were found to be dependent on chemical composition of the samples. Solid solutions with orthorhombic structure revealed higher magnetization values compared to those of hexagonal samples. The highest magnetization was observed for pure GdMn0.97Fe0.03O3. Structural properties were investigated by powder X-ray diffraction, Mössbauer, FTIR and Raman spectroscopies. Morphological features of the synthesized specimens were studied by scanning electron microscopy (SEM).