Low-temperature Magnetic Properties Research Articles

Magnetic Single‐Ion Anisotropy and Curie‐Weiss Behaviour of Mg3V4(PO4)6

AbstractDirect current (DC) magnetometry data obtained for polycrystalline Mg3V4(PO4)6 were fitted by various magnetic models based on angular momentum basis states. As a result, single‐ion anisotropy of the magnetic V 3+ ions could be identified to decisively determine the magnetic properties of Mg3V4(PO4)6 and not antiferromagnetic exchange interaction between V ions as supposed in literature. It could be demonstrated analytically, by utilization of the Van Vleck equation, that also single‐ion anisotropy can lead to a linear and origin shifted inverse susceptibility curve in the high temperature region. The Weiss constant obtained from a Curie‐Weiss fit to such a susceptibility curve might falsely be ascribed to antiferromagnetic exchange interactions if additional low temperature magnetic properties are not considered for verification.

Low-temperature properties of magnetically frustrated rare-earth zirconates A 2Zr2O7

Rare-earth A 2Zr2O7 zirconates have attracted considerable attention of the scientific community for their complex magnetic, electronic and material properties applicable in modern technologies. The light rare-earth members of the series, crystallising in the pyrochlore variant of cubic crystal structure, have been studied in detail. The heavier A 2Zr2O7 compounds have been investigated mainly from the material properties viewpoint, focussing on their thermal properties and stability at high temperature and pressure. Low-temperature studies were mostly missing until recently. We present the low-temperature magnetic and thermodynamic properties of A 2Zr2O7 with A = Y, La, Nd, Eu, Gd, Tb, Dy, Ho, Tm, Yb, and Lu, well covering the whole series, newly synthesised by high-temperature sintering and melting methods. X-ray diffraction reveals and confirms the ordered pyrochlore structure in the light members, the disordered cubic structure of the defect-fluorite type in A 2Zr2O7 with A = Y, Gd–Yb, and finally the lower symmetry rhombohedral structure in the end-member Lu2Zr2O7. The specific heat of the investigated compounds is dominated by a low-temperature anomaly associated with magnetic ordering: long-range in light rare-earth zirconates; and short-range in heavier members. The effective magnetic moment in the studied compounds, determined by fitting the magnetisation data to the Curie–Weiss formula, is in good agreement with the expected value of the A 3+ free ion. The magnetic properties have been revealed to be strongly influenced by the geometric frustration of the magnetic moments of both the pyrochlore structure, as well as the face centred cubic lattice created by the cations of the defect-fluorite structure, but connected also to intrinsic atomic disorder. The experimental results are discussed in the framework of previous studies on A 2Zr2O7 zirconates, as well as other A 2 B 2O7 compounds.

Magnetic and thermoelectric properties of quasi-one-dimensional BaVSe3

Quasi-one-dimensional (Q1D) materials possess extraordinary magnetic and transport characteristics, which render them of critical importance. In this study, we present the synthesis of phase pure Q1D BaVSe3 via a novel heat treatment process and analyze its low-temperature thermoelectric, magnetotransport, and magnetic properties. A comparison is made between this phase pure system and the BaVSe3 infused with the secondary BaSe3 phase that we previously reported todetermine the potential effect of impurities on the magnetic and thermoelectric properties. Our previous study covered the experimental and theoretical investigation on the exotic magnetic properties of BaVSe3 with BaSe3. In phase pure BaVSe3, at TC ∼ 41.2 K, a paramagnetic to ferromagnetic transition with a magnetic moment of 1.74 μB from V4+ was observed,consistent with calculated values. At very low temperatures (<117 K), the material behaved like glass, showed Griffiths-like behaviorand spin valve-like butterfly magnetoresistance (BMR). Experiments indicate that these exotic magnetic properties are caused by the interaction between the A1g and t2g levels of the V 3d orbital and their spin orientation. Magnetic frustration in these materials is caused by V-V inter and intra chain interactions in the 1D spin chains of V. Q1D BaVSe3 (BVS) demonstrated n-type thermoelectricity with a thermoelectric figure of merit of ∼ 0.008, 4 × greater than BaVSe3:BaSe3 (BVS: BS) at room temperature. The thermal transport is determined to be primarily phonon-dependent. The magnetic property studies disclosed that this FM transition metal chalcogenide can contribute to low-temperature spintronics.

Low temperature heat capacities and magnetic properties of anhydrous and hydrated forms of manganous sulfate (MnSO4)

Manganese (II) sulfate (MnSO4), also known as manganous sulfate, has gained attention due to its low temperature magnetic properties. Following a study of its magnetic structure, manganese sulfate was proposed as being the first orthorhombic compound to have a spiral magnetic structure. It was predicted to have a three-step magnetic transition at low temperatures, which neutron diffraction studies have since confirmed. This work represents the first time that heat capacity data has been collected on MnSO4 and MnSO4 0.984(H2O) at low temperatures, which we report from 1.8 K to 300 K and comment on the presentation of the magnetic transition in the low temperature heat capacity region. Previous studies report the heat capacity of the anhydrous form above 50 K, and the data collected herein is compared with those previously published results. Theoretical fits of the heat capacity data are used to calculate the smoothed thermodynamic data, including Cp,m°, Δ0TSm°, Δ0THm°, andΦm°.

Influence of the Rare Earth Cation on the Magnetic Properties of Layered 12R-Ba4M4+Mn3O12 (M = Ce, Pr) Perovskites.

Material design is increasingly used to realize desired functional properties, and the perovskite structure family is one of the richest and most diverse: perovskites are employed in many applications due to their structural flexibility and compositional diversity. Hexagonal, layered perovskite structures with chains of face-sharing transition metal oxide octahedra have attracted great interest as quantum materials due to their magnetic and electronic properties. Ba4MMn3O12, a member of the "12R" class of hexagonal, layered perovskites, contains trimers of face-sharing MnO6 octahedra that are linked by a corner-sharing, bridging MO6 octahedron. Here, we investigate cluster magnetism in the Mn3O12 trimers and the role of this bridging octahedron on the magnetic properties of two isostructural 12R materials by systematically changing the M4+ cation from nonmagnetic Ce4+ (f0) to magnetic Pr4+ (f1). We synthesized 12R-Ba4MMn3O12 (M= Ce, Pr) with high phase purity and characterized their low-temperature crystal structures and magnetic properties. Using substantially higher purity samples than previously reported, we confirm the frustrated antiferromagnetic ground state of 12R-Ba4PrMn3O12 below TN ≈ 7.75 K and explore the cluster magnetism of its Mn3O12 trimers. Despite being atomically isostructural with 12R-Ba4CeMn3O12, the f1 electron associated with Pr4+ causes much more complex magnetic properties in 12R-Ba4PrMn3O12. In 12R-Ba4PrMn3O12, we observe a sharp, likely antiferromagnetic transition at T2 ≈ 12.15 K and an additional transition at T1 ≈ 200 K, likely in canted antiferromagnetic order. These results suggest that careful variation of composition within the family of hexagonal, layered perovskites can be used to tune material properties using the complex role of the Pr4+ ion in magnetism.

Strain-induced magnetic anisotropy of multi-domain epitaxial EuPd2 thin films

Europium intermetallic compounds show a variety of different ground states and anomalous physical properties due to the interactions between the localized 4f electrons and the delocalized electronic states. Europium is also the most reactive of the rare earth metals which might be the reason why very few works are concerned with the properties of Eu-based thin films. Here we address the low-temperature magnetic properties of ferromagnetic EuPd2 thin films prepared by molecular beam epitaxy. The epitaxial (111)-oriented thin films grow on MgO (100) with eight different domain orientations. We analyze the low-temperature magnetic hysteresis behavior by means of micromagnetic simulations taking the multi-domain morphology explicitly into account and quantify the magnetic crystal anisotropy contribution. By ab initio calculations we trace back the microscopic origin of the magnetic anisotropy to thin film-induced uniform biaxial strain.

Study of structural, X-ray photoelectron spectroscopy, Raman and temperature-dependent magnetic studies of NiFe2O4/CoCr2O4 nanocomposites

In recent years, cobalt chromites/nickel ferrites have been attractive candidates for significant applications as nanomagnets. In the present work, structural, electronic, vibrational and low-temperature magnetic properties of NiFe2O4, CoCr2O4, and NiFe2O4/CoCr2O4 nanocomposites were investigated. Refined XRD patterns and the Raman spectra confirm the formation of the pure crystalline spinel cubic phase. The estimated crystallite size is in the range of 14 - 29 nm. X-ray photoelectron spectroscopy (XPS) confirm the oxidation state of all elements present in the synthesized samples. The studies of the photoemission core level lines prove the cations distribution in the tetrahedral and octahedral sites with the expected valence states. The magnetic studies reveal the S-type hysteresis loops, confirming the ferrimagnetic nature. The remanent and saturation magnetization increase with increasing NiFe2O4 concentration and decrease with increasing temperature. The magnetization also increases with increase of crystallite size. The temperature-dependent magnetization curve of CoCr2O4 shows the ferrimagnetic phase transition at Curie temperature TC = 86 K. The performed density functional theory (DFT) calculations indicate a significant distribution of the density of states over the Fermi level in NiFe2O4/CoCr2O4 composites as compared to bare NiFe2O4 and CoCr2O4 materials, confirming the improved electronic properties. The overall magnetic analysis proved the magnetization enhancement by increasing x concentration.

Magnetic and thermodynamic study of the interplay between magnetism and structure in CrOCl

Magnetic materials associated with the structural phase transition has brought considerable interest. CrOCl is found to provide a fertile setting for studying the interplay between magnetism and atomic structure. In particular, its magnetic ordering transition has been observed accompanying by an orthorhombic-to-monoclinic structural transition, yet the detailed thermodynamic properties of this transition remain to be further investigated. Here, by systematically measuring the low temperature magnetic properties of CrOCl, we observe thermal hysteresis behaviors in both temperature and magnetic field scans, demonstrate the first-order nature of such a complex phase transition. The entropy change during the phase transition is also estimated by two different methods, providing further quantitative characterizations of it. Our results thus not only give detailed insights on the phase transition involving both magnetism and structure, but also imply its potential for applications in, for example, magnetic refrigeration.

Signature of elementary excitations in Se-substituted layered triangular-lattice antiferromagnet CuCrS2

Geometrical spin frustration in a layered triangular-lattice system prohibits the long-range magnetic order and could give rise to unusual spin-disordered states of matter in which spins are strongly correlated and highly entangled with low-energy excitations. Here we investigate the low-temperature magnetic and specific heat properties of the layered triangular-lattice system CuCr(S1-xSex)2 within the entire Se-for-S substitution range. In magnetization measurements, the x = 0 phase exhibits a sharp cusp-like antiferromagnetic transition at 38 K, while for all the Se-substituted samples a broad maximum along with a spin-glass-like freezing at low temperatures is seen. The Curie-Weiss temperature systematically increases from −122 K for x = 0 to + 15 K for x = 1. These observations suggest that the magnetic ground state is determined by the competition between antiferromagnetic direct exchange interactions and ferromagnetic super-exchange interactions. For x = 0, the magnetic contribution to heat capacity exhibits a sharp jump at the magnetic transition temperature indicative of 3D long-range magnetic order, while for the x > 0 samples it increases smoothly across the magnetic transition range following a power-law (∼T2.1) behavior. All these results are in line with an existence of unusual gapless spin-liquid like excitations originating from the spin frustrations and competing nearest-neighbor interactions in CuCr(S,Se)2.

A comprehensive study of dielectric, magnetic and anticancerous properties of lanthanum manganite perovskite nanoparticles

Present study reports the combustion synthesis of lanthanum manganite (LaMnO3) perovskites with rhombohedral structure having R-3 C space group. The structural and morphological evaluations of synthesized nanoparticles were done by XRD, FTIR, SEM and XPS. The BDS analysis reveals different types of polarization associated with dielectric properties. Frequency-dependent dielectric properties such as dielectric constant, dielectric loss, ac conductivity and capacitance were analyzed at room temperature. BDS analysis explain Maxwell-Wagner effect and Jhonscher universal power law. Room temperature and low temperature magnetic properties were investigated using VSM. M(T) measurements shows second order phase transition from ferromagnetic (FM) to paramagnetic (PM) at 230 K Curie temperature. The detailed magnetic characteristics of lanthanum manganite perovskites were clearly explained by Curie – Wiess and Arrott’s plot. The hyperthermial behavior were studied with normal and pre-heated LaMnO3. The in - vitro anticancerous analysis were explained by MTT assay. The LC50 values of normal and preheated specimens are 124.145 µg/ml and 86.159 µg/ml, respectively. The reduction in LC50 value of preheated sample underscores its superior anticancer efficacy compared to normal sample.

Impact of cation distribution on structural, morphological, optical and low-temperature magnetic properties of Er3+ substituted Cu0.8Cd0.2Fe2O4 nanoparticles

A series of cubic spinel-shaped Cu-Cd ferrites using Er3+ ion doping, Cu0.8Cd0.2ErxFe2-xO4 (x = 000, 0.0010, 0.0015, 0.0020, 0.0025, and 0.0030-CCEF) had been synthesized using the citrate sol-gel auto combustion approach. The structural, optical and magnetic properties of the samples were investigated using a wide range of characterization techniques, such as Thermogravimetric and Differential thermal analysis (TG-DTA), Powder x-ray diffractometer (P-XRD), High-resolution transmission electron microscopy (HR-TEM), UV–VIS, Electron spin resonance (ESR), and Vibrating sample magnetometer (VSM). To obtain an understanding of the existence of hydrated water and comprehend the degradation behavior, the TG-DTA was carried out. The produced powders were then sintered for 240 min at 500 °C. According to X-ray diffraction spectra, the John-Teller ion (Cu2+) causes a tetrahedral deformation for pure Cu-Cd ferrite. Erbium substituted afterwards transformed the tetragonal phase towards the cubic spinel phase including trace amounts of impurity phase. FESEM and HRTEM analysis were employed to investigate the microstructure. These FESEM and HRTEM images' observations demonstrated that nanoparticles have a spherical shape. Furthermore, the findings showed that the as-prepared spinel Cu-Cd ferrite nanoparticles exhibited a determined optical band gap energy in the region of 1.62–1.91 eV, demonstrating the semiconducting properties of the synthesized materials. In order to calculate the spin resonance parameters such as the g-values, peak-to-peak linewidth and resonance field, ESR spectra accumulated with X-band microwave energy have been fitted using the Lorentzian function. At 15 K, an in-depth examination of the ferrite nanoparticles' magnetic characteristics was performed. The prepared sample has shown indications of developing superparamagnetic behavior.

Role of A site and B site ion substitutions on the low-temperature magnetic behaviour of Ca2Fe2O5

In the present paper, we report the structural and low-temperature magnetic properties of Sm-substituted Ca2Fe2O5 (Ca2(1-x)Sm2xFe2O5, x = 0.05, 0.1) and Co-substituted Ca2Fe2O5( Ca2Fe2(1-y)Co2yO5, y = 0.1, 0.2). The polycrystalline samples of Sm and Co-based compounds, synthesised by a solid-state reaction route, are found to be crystallised with space group Icmm and Pnma respectively. The gradual substitution/doping of Sm3+ (5 % and 10 %) replacing Ca shows a significant change in temperature dependant magnetic behaviour, assumed to originate from complex interactions of Sm and Fe ions. For Co-substituted samples, the magnetic study as a function of temperature suggests the signature of ferri/ferromagnetic interactions along with the probable signature of a glassy feature. Isothermal magnetisation characterisations indicate the pure antiferromagnetic interactions in Sm samples, whereas the onset of hysteresis in Co samples can be correlated with the ferri/ferromagnetic nature of samples with the antiferromagnetic ground state.

Structural, dielectric, thermoelectric, and magmatic properties of Er3+ ion substituted Mg-Zn spinal nanoferrites: High charge-storage capacitors and high-frequency microwave device applications

The Er-substituted magnesium and zink ferrite nanomaterials with the chemistry formula Mg0.8Zn0.2ErxFe2-xO4 (x = 0.00, 0.005, 0.01, 0.015, 0.02, 0.025) were generated in the study utilizing the citrate-gel auto combustion method. XRD is being used to investigate the cubic spinal structural structure. A transmission electron microscope (TEM) and a field emission scanning electron microscope (FESEM) were used to examine surface morphology. From the structural studies, the crystal sizes range from 14.46 to 96.40, with lattice parameters ranging from 8.434 to 8.449 and X-ray density (gm/cc) ranging from 4.585 to 4.671 and porosity (%) ranging from 7.67 to 7.91. The resulting macrostrain produces internal tension and can impair material grain growth. UV–visible absorption spectroscopy gives grain size pictures as well as quantifications at 300 K and 100 K, respectively. The wavelength range cut-off from 537.6 nm to 270.9 nm. The dielectric characteristics of the samples were tested at room temperature using an LCR meter at various frequencies. The dielectric parameters include the real component of the dielectric constant, the dielectric constant's imaginary portion, and the loss tangent. For each sample, the loss tangent of nanoferrites fell as the frequency increased. This type of material is used in capacitors and microwave devices. Thermoelectric power studies measured all samples. From the studies observed, the seeback coefficient decreases with increasing temperature and Er doping. The room temperature and low temperature magnetic properties were studied at 300 k and 100 k at low temperature ZFC and FC. The blocking temperature Tb was around 300 K.

Low Temperature Magnetic Properties of Variably Oxidized Natural and Synthetic Siderite

AbstractSiderite (FeCO3) is an important ferrous iron carbonate in the geochemical cycling of iron, as it is a sink for iron under reducing conditions. However, its detection is not straightforward with classical analytical approaches because in natural samples it is often fine‐grained and/or occurs in low concentrations. In this study, we explore the analytical potential of low‐temperature magnetometry. Synthetic siderites with a limited amount of associated ferric iron of up to 5 mol% and some natural siderites were subjected to investigation. Maxima in the cooling curves in a 5 T magnetic field shows that the Néel temperature of siderite is at 37 K in agreement with literature data. Those maxima appear at a higher temperature in the synthetic siderites with associated/sorbed ferric iron; it is 45 K for the 5 mol% Fe3+ synthesis. With the increasing amount of ferric iron, the synthetic siderites show an increasingly prominent remanence tail beyond the nominal Néel temperature in field‐cooled (FC) and zero‐field‐cooled (ZFC) warming curves of the remanent magnetization acquired in 5 T at 5 K. Fine‐grained siderite alters in air on laboratory time scales which is manifested by more pronounced remanence tails up to higher temperatures. Siderite's presence is best diagnosed by evaluating a combination of FC warming curves and a FC/ZFC remanence ratio &gt;3 at 5 K. Standard addition experiments of FC warming curves enable the determination of siderite down to 0.1 wt%.

Impact of Process Parameters and Dopant Concentration on Structural, Magnetic, and Dielectric Properties of Dysprosium-doped Nickel-Zinc Ferrites Synthesized by Microwave Hydrothermal Method

This study aims to investigate the impact of substituting Dy3+ ions on the structural, magnetic and dielectric properties of Nickel Zinc (Ni-Zn) ferrites, which have the chemical formula Ni0.5Zn0.5DyxFe2-xO4 (where x = 0, 0.01, 0.03, 0.05, 0.07, and 0.09). These ferrites were synthesized using a microwave hydrothermal technique with different process parameters. Structural characterization of the synthesized powders was carried out using X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FTIR). The XRD analysis confirmed the presence of a pure spinel phase for Dy concentrations (x) up to 0.05. However, when x ≥ 0.07, an additional orthoferrite phase (DyFeO3) was observed along with the spinel phase. FTIR spectra revealed a shift in low-frequency wave numbers due to Dy3+ ion substitution. The size and morphology of the synthesized powder particles were examined using field emission scanning electron microscopy (FESEM). The powder compacts were sintered using microwave processing at 900 °C for 40 min. The increase in dc. resistivity is observed with an increase in Dy3+ concentration, mainly due to the change in the hopping mechanism with the substitution concentration. Dielectric properties such as dielectric constant and loss are measured in the frequency range of 100 Hz to 1.8 GHz. The high value of dielectric constant and loss observed in the low-frequency region compared to the high-frequency region. Maxwell’s Wagner model and ‘Koop’s theory explains the variation in dielectric properties with the frequency. The magnetic hysteresis loops were measured at different temperatures and observed to enhance the low-temperature magnetic properties compared to room temperature. The results suggest that the magnetic and dielectric properties of the investigated samples can be adjusted by varying the concentration of Dy3+ ions, providing the ability to tailor these properties according to specific application requirements.

Tracing titanomagnetite alteration with magnetic measurements at cryogenic temperatures

SUMMARY Titanomagnetite containing up to 0.6–0.7 Ti atoms per formula unit is a primary magnetic mineral phase in submarine basalts and in some terrestrial volcanic rocks. On a geological timescale, it often undergoes alteration, forming new magnetic phases that may acquire (thermo)chemical remanent magnetization. The initial stage of this natural process can be modelled by prolonged laboratory annealing at moderately elevated temperatures. In this study, our goal is to characterize the alteration products resulting from annealing a submarine basalt containing homogeneous titanomagnetite Fe3−xTixO4 (x ≈ 0.46) at temperatures of 355, 500 and 550 °C for up to 375 hr, by examining their magnetic properties over a wide range of temperatures. The effect of extended annealing is most apparent in the low-temperature magnetic properties. In the fresh sample, a magnetic transition is observed at 58 K. Below the transition temperature, the field-cooled (FC) and zero-field-cooled (ZFC) saturation isothermal remanent magnetization (SIRM) curves are separated by a tell-tale triangular-shaped area, characteristic for titanomagnetites of intermediate composition. The room-temperature SIRM (RT-SIRM) cycle to 1.8 K in zero field has a characteristic concave-up shape and is nearly reversible. For the annealed samples, the magnetic transition temperature shifts to lower temperatures, and the shape of the curves above the transition changes from concave-up to concave-down. The shape of the RT-SIRM cycles also progressively changes with increasing annealing time. The SIRM loss after the cycle increases up to ∼30 per cent for the samples annealed for 375 hr at 355 °C, and for 110 hr at 500 and 550 °C. The Curie temperatures of the newly formed magnetic phases exceed the Curie temperature of the fresh sample (205 °C) by up to 350 °C. While this effect is most commonly attributed to extensive single-phase oxidation (maghemitization), the behaviour observed at cryogenic temperatures appears incompatible with the known properties of highly oxidized titanomaghemites. Therefore, we propose that, at least in the initial stage of the ‘dry’, that is, not involving hydrothermalism, alteration of titanomagnetite, temperature- and time-controlled cation reordering is the primary mechanism driving changes in both low- and high-temperature magnetic properties.

Charge order, frustration relief, and spin-orbit coupling in U3O8

Research efforts on the description of the low-temperature magnetic order and electronic properties of ${\mathrm{U}}_{3}{\mathrm{O}}_{8}$ have been inconclusive so far. Reinterpreting neutron scattering results, we use group representation theory to show that the ground state presents collinear out-of-plane magnetic moments, with antiferromagnetic coupling both in-layer and between layers. Charge order relieves the initial geometric frustration, generating a slightly distorted honeycomb sublattice with N\'eel-type order. The precise knowledge of the characteristics of this magnetic ground state is then used to explain the fine features of the band gap. In this system, spin-orbit coupling (SOC) is of critical importance, as it strongly affects the electronic structure, narrowing the gap by $\ensuremath{\sim}38%$, compared to calculations neglecting SOC. The predicted electronic structure actually explains the salient features of recent optical absorption measurements, further demonstrating the excellent agreement between the calculated ground state properties and experiment.

Energy spectrum and magnetic properties of the decorated spin ladder models of nanomagnets on the base of polymeric transition metal compounds

The work is devoted to the theoretical study of the energy spectrum and low-temperature magnetic properties of the decorated spin-ladder model with the polyacene topology and the three types of the site spins. On the base of cluster expansion technique an approximate analytical treatment of lowest part of the energy spectra of two isomeric ladder structures was given. It is shown that the ladder model with singlet ground state is more stable than its isomeric analog with the macroscopic ground state spin. In addition, the numerical study of field dependence of low-temperature magnetization of 8- spin clusters of both ladder models was performed by means of exact diagonalization method. On the base of these results, it was shown the presence of an intermediate plateau in low-temperature magnetization profile of the above spin ladder models.

The energy spectrum and low-temperature magnetic properties of the decorated two-leg mixed spin ladder

The energy spectra and low-temperature magnetic properties of two one-dimensional Heisenberg mixed spin (s = 1, 1/2) systems, namely decorated two-leg mixed spin ladders with the lattice topology of polyacene, are studied. The gapless character of the exact excitation energy spectra for both ladder models has been determined. We found numerically that the model with macroscopic ground state spin S0 has gapped excitations with the spin S &amp;gt; S0. This leads to the appearance of an intermediate plateau in field dependence of magnetization at low temperatures. We have shown that the ladder with equal coupling in legs has the maximal size of this plateau at the same coupling in rungs. For a mixed spin ladder model with Ising interactions in legs, the appearance of two intermediate magnetization plateaus at low temperatures and some values of coupling parameters was shown.

Exploring oxygen non-stoichiometry in presumably stoichiometric double perovskites: the case study for LaCu0.5Mn0.5O3-δ

Perovskite-like oxide with the general formula LaCu0.5Mn0.5O3–δ (LCMO) was synthesized via the combustion of organo-metallic precursors. X-ray powder diffraction and high-resolution transmission electron microscopy were implemented for reliable characterization of the crystal structure of the sample obtained. Accordingly, disordered cation arrangement in B-sublattice was detected. The studied specimen was confirmed to possess non-zero oxygen vacancy concentrations at reductive annealings which were shown to modify LCMO's low-temperature magnetic properties. Density functional theory approach was also applied to assess the symmetry of the crystalline lattice and to analyze the influence of cationic order on LCMO electronic and magnetic structure. Anionic sites allocated between varying cation types were shown to possess sufficiently different vacancy formation energies and, therefore, the varied ability to release oxygen into the gas phase. The obtained results were taken into account at developing theoretical model of defect formation and equilibration in LCMO. The proposed concept was validated by a good coincidence between the experimental results on isothermal dependencies of oxygen content vs external conditions (temperature and oxygen partial pressure) and the calculations performed. Thermodynamic properties were also shown to be strongly dependent on cation ordering type. The obtained results are believed to be useful for the interpretation of dielectric and optical properties of LCMO and related oxide materials inclined to possess oxygen non stoichiometry at high temperatures.