Superparamagnetic Phase Research Articles

Antiferromagnetism, superparamagnetism, and effects of A-cation distribution on magnetic properties of LaSrFeO[formula omitted] Ruddlesden–Popper oxides: A combined experimental and theoretical study

Understanding the structure–property relationship in complex magnetic oxides is crucial for developing new magnetic materials. In this study, we synthesized LaSrFeO4 Ruddlesden–Popper oxide using spray-pyrolysis method. Electron paramagnetic resonance (EPR) spectra revealed two Fe-associated lines: a broad line indicating short-range antiferromagnetic (AFM) order, disappearing at 375 K, and a narrow line due to the presence of superparamagnetic phase. The magnetic moment from the linewidth’s temperature dependence was 10−19 A m2. EPR intensity analysis estimated the superparamagnetic to antiferromagnetic phase ratio at 0.014 ± 0.004.Using density-functional theory with Agapito–Curtarolo–Buongiorno–Nardelli (ACBN0) pseudo-hybrid functional including self-consistent Hubbard U correction, we calculated the density of states for two La/Sr atomic distributions. The calculations show that a uniform La/Sr distribution perturbs 2D symmetry of Fe 3d states, which can contribute to the observed lowering of the critical exponent β for the magnetically ordered phase. These results highlight the impact of La/Sr distribution on LaSrFeO4’s properties.

Structural, morphological, and magnetic characterizations of (Fe0.25Mn0.75)2O3 nanocrystals: A comprehensive stoichiometric determination

This report aims to investigate in depth FeMnO3, a material of interest due to its fascinating magnetic and multiferroic properties and its many applications in fields including lithium-ion batteries, microwave devices, and catalysis. However, understanding the precise stoichiometry of the material is crucial for a better comprehension of its physical properties. A cheap, simple, and repeatable sol-gel process was used to fabricate the FeMnO3 nanocrystals. Comprehensive multi-technique characterization of the as-fabricated FeMnO3 indicates that the main phase (94 wt%) is Fe0.5Mn1.5O3, although hematite appears as the minority phase (6 wt%). Magnetic characterization shows core-shell spin-glass like behavior, as well as paramagnetic-ferrimagnetic transitions and a Griffiths phase regime. EPR measurements revealed a strong and broad resonance line across the temperature range of 4.3 K–300 K, primarily influenced by the majority phase. The g-value decreases monotonically from 2.93 at 50 K to 2.18 at 300 K. There is a notable change in the resonance field and linewidth between 40 and 50 K, attributed to surface spin glass behavior. The EPR data below 50 K are in line with the core-shell model of (Fe0.25Mn0.75)2O3 nanoparticles. Below 50 K, the shell's spin system undergoes a transition from paramagnetic to spin-glass-like, with a critical temperature around 43 K. Above 50 K, the superparamagnetic minority phase significantly affects the temperature dependence of the resonance linewidth. These results hold particular importance as they advance our understanding of the intricate magnetic interactions present in FeMnO3. For the best possible use of this material platform in new technologies, such insights are essential.

Effect of cobalt and aluminum doping on the structural and magnetic properties of zinc oxide nanoparticles

A systematic study of the substitution effect of Co and Al on ZnO nanoparticles was carried out by x-ray diffraction (XRD) and transmission electron microscopy and using a superconducting quantum interference device magnetometer to study their structural, morphological, and magnetic properties. Zn1−xMxO (M = Co, Al) at different doping concentrations was prepared using a hydrothermal technique. The XRD results with structural Rietveld refinement reveal that the major phase of all samples had a hexagonal wurtzite crystal structure with a P63mc space group. Hysteresis loops with no magnetic saturation at high fields were analyzed at 2 K in all samples. Zero magnetic remanence and zero coercivity were also examined. The results demonstrated that the magnetic ground state at 2 K in all samples was magnetism with the coexistence of antiferromagnetic, ferromagnetic, and superparamagnetic phases. This behavior persisted at 100 and 300 K in the Al-doped sample, while Co-doped ones exhibited a paramagnetic state only. The role of non-magnetic doping, which leads to the appearance of magnetism in ZnO nanoparticles persisting at high temperatures, is discussed herein.

Size dependent structural and magnetic properties of Co(1−x) Nix Cr2O4 nanoparticles (x = 0.15, 0.20)

This study examines the structural and magnetic characteristics of Co(1−x)NixCr2O4 (x = 0.15, 0.20) compounds synthesised using the co-precipitation technique and calcined at 500 °C and 900 °C respectively. X-ray diffraction studies reveal the structure of the synthesized samples is face-centered cubic with space group Fd-3m. The particle sizes and morphology were examined by using transmission electron microscopy, and the size ranges from 64 ± 10 nm to 105 ± 15 nm for the 900 °C and 7 ± 2 and 8 ± 2 nm for the 500 °C calcined samples. Field-cooling and zero-field-cooling magnetization measurement protocols were used to investigate the materials' magnetic characteristics. The Curie temperature (TC) decreases from 91 ± 0.5 K to 85 ± 0.3 K as the Ni concentration increases from x = 0.15–0.20. Additionally, an increase in the TC value is seen for both compositions when the particle size is decreased. Spiral ordering is observed at a transition temperature TS for the samples calcined at 900 °C, while no evidence for TS was seen for samples calcined at 500 °C. Magnetization measurements as a function of field, Mμ0H, at several constant temperatures, show that the coercivity reduces with an increase in temperature in all samples. The Co(1−x)NixCr2O4 (x = 0.15, 0.20) samples calcined at 900 °C exhibit superparamagnetic behaviour with a small ferrimagnetic hysteresis loop. Furthermore, this paper evaluates the contribution of ferrimagnetic, superparamagnetic, and paramagnetic phases to the total Mμ0H curve for Co(1−x)NixCr2O4 (x = 0.15, 0.20) calcined at 900 °C through simulation. In addition, a modified Langevin simulation, incorporating a particle size distribution term, is performed for the Co(1−x)NixCr2O4 (x = 0.15, 0.20) samples calcined at 500 °C. From the simulations, it is clear that all samples show evidence of significant superparamagnetic contributions to the total saturation magnetization because of the small particles present.

Novel Magnetic Levitation of Nanoiron Oxide for Dynamically Measuring Crystallinity and Uniformity

This study explores the magnetic levitation (maglev) characteristics of superparamagnetic iron oxides (Fe3 O4 ) used as motor-driven rotors in gyroscopes under low-alternating magnetism. Herein, superparamagnetic Fe3 O4 was synthesized in a nanopowder form using the sol–gel method. The maglev force that stabilizes a rotating gyroscope depends on the rotation speed. This force exhibits a wide range of values. The stability of the synthesized superparamagnetic Fe3 O4 increases with its size. The rotation stability was measured based on the size of a red laser spot and was found to depend on the rotation speed. Under a low magnetic field, superparamagnetic materials exhibit high stability. Herein, the superparamagnetic phase exhibits excellent stability. With increasing rotation speed, the superparamagnetic material exhibits strong magnetization. The nanoiron oxide is used to dynamically measure crystallinity and uniformity. Additionally, inversion recovery shows improved gyrostabilization for the superparamagnetic material.

Structure, Mössbauer, electrical, and γ-ray attenuation-properties of magnesium zinc ferrite synthesized co-precipitation method

For technical and radioprotection causes, it has become essential to find new trends of smart materials which used as protection from ionizing radiation. To overcome the undesirable properties in lead aprons and provide the proper or better shielding properties against ionizing radiation, the tendency is now going to use ferrite as a shielding material. The co-precipitation method was utilized to prevent any foreign phases in the investigated MZN nano-ferrite. X-ray diffraction (XRD) and Fourier transmission infrared spectroscopy (FTIR) methods were used to analyze the manufactured sample. As proven by XRD and FTIR, the studied materials have their unique spinel phase with cubic structure Fd3m space group. The DC resistivity of Mg–Zn ferrite was carried out in the temperature range (77–295 K), and its dependence on temperature indicates that there are different charge transport mechanisms. The Mössbauer spectra analysis confirmed that the ferrimagnetic to superparamagnetic phase transition behaviour depends on Zn concentration. The incorporation of Zn to MZF enhanced the nano-ferrite density, whereas the addition of different Zn-oxides reduced the density for nano-ferrite samples. This variation in density changed the radiation shielding results. The sample containing high Zn (MZF-0.5) gives us better results in radiation shielding properties at low gamma, so this sample is superior in shielding results for charged particles at low energy. Finally, the possibility to use MZN nano-ferrite with various content in different ionizing radiation shielding fields can be concluded.

The effect of hydrogen pressure on magnetic properties of Zr2(Co0.5Fe0.2Ni0.2V0.1) alloy

The influence of hydrogen pressure on the magnetic and microstructure properties of Zr2(Co0.5Fe0.2Ni0.2V0.1) alloy was investigated in low and high hydrogen pressure. XRD and Rietveld refinement analysis of the as-cast alloy shows a multiphase crystal structure, mainly consisting of the C16 tetragonal phase. Mössbauer spectra and magnetic measurements confirmed a formation of interacting superparamagnetic clusters within a paramagnetic matrix. A typical spin glass-like transition was observed at blocking temperature below 30 K. Hydrogenation shows a significant increase in the magnetic properties. Under low hydrogen pressure (hydrogen content ∼19 mmol/gr), a ferromagnetic hysteresis loop was observed without any significant change in the crystal structure, indicating that exchange interaction between clusters increased markedly by hydrogenation. In high hydrogen pressure (hydrogen content ∼42 mmol/gr), the disproportionation reaction altered both the crystal structure and the magnetic property of the alloy. The presence of at least two interacting superparamagnetic phases within the paramagnetic matrix can be represented by fitting the M(H) data to the theoretical model. This study discusses a complex case of magnetic clusters embedded in a paramagnetic matrix and is a good example of drastic changes of magnetic properties by hydrogenation.

Highly covalent FeIII–O bonding in photo-Fenton active Sn-doped goethite nanoparticles

The relationship between local structure and photo-Fenton catalytic ability of tin-doped goethite with the composition of α-SnxFe1-xOOH (x = 0, 0.05, 0.10, 0.15 and 0.20, abbreviated as Sn100x) was investigated by X-ray diffractometry (XRD), 57Fe-and 119Sn-Mössbauer spectroscopies, X-ray absorption near-edge spectroscopy (XANES), transmission electron microscopy (TEM), Brunauer–Emmett–Teller surface area measurement (BET), diffuse reflectance spectroscopy (DRS), and ultraviolet–visible absorption spectroscopy (UV–vis). Room temperature 57Fe-Mössbauer spectra of Sn0 and Sn5 showed a sextet with isomer shift (δ) of 0.37 mm s−1, quadrupole splitting (Δ) of −0.27 mm s−1, and internal magnetic field (Hint) of 33.2 T due to goethite. In contrast, those of Sn10, Sn15 and Sn20 showed a doublet with increasing δ from 0.34 to 0.37 mm s−1 and Δ from 0.62 to 0.63 mm s−1 due to the superparamagnetic phase. On the other hand, increasing δ from −0.01 to 0.13 mm s−1 and decreasing Δ from 1.15 to 0.53 mm s−1 was observed from the 119Sn-Mössbauer spectra of Sn100x with ‘x’ from 0.05 to 0.20. These results indicate that the SnIV–O chemical bond becomes shorter, while that of FeIII–O longer by introducing tin into goethite, which causes a decrease in the bandgap energy (Eg). TEM image of Sn100x showed that needle-like particles with an average length of 181 and 61 nm were respectively observed in Sn0 and Sn5, whereas nanoparticles with the average size of 4.1, 6.4 and 10.2 nm were for Sn10, Sn15 and Sn20, respectively. From the BET measurement, the specific surface area (SSA) of Sn100x increased from 53 to 178 m2 g−1 with Sn concentration. Photo-Fenton catalytic ability of Sn100x using 20 μmol L−1 methylene blue aqueous solution and 0.4 mol L−1 H2O2 under visible-light irradiation revealed that Sn15 showed the largest apparent-first-order rate constant (k) of 35•10−3 min−1. We conclude that Sn15 is the best catalyst because of its large SSA of 187 m2 g−1 and the smallest bandgap energy of 1.77 eV.

Superparamagnetism and ferrimagnetism in the Sr2FeMoO6–δ nanoscale powder

Using combined synthesis modes and optimized conditions for ultrasonic dispersion, we obtained a single-phase nanosized Sr2FeMoO6–δ powder having a high degree of superstructural ordering of Fe and Mo cations (88 %) and an average grain size of 70.8 nm. The results of the Mössbauer spectroscopy and magnetic measurements show that the obtained nanosized strontium ferromolybdate powder is in a magnetically inhomogeneous state, consisting of superparamagnetic and ferrimagnetic phases. In comparison with the superparamagnetic component of magnetization, the ferrimagnetic component has higher values and rises smoothly until reaching saturation as the temperature decreases. Showing that there is no exchange magnetic interaction between the grains in the superparamagnetic phase, allowed us to estimate the critical sizes, of nanoparticles, dspm, in the single-domain state using the Néel-Brown model. The obtained value of dspm is smaller than the size of the single-domain particles, which confirms the absence of the frozen state in some of the superparamagnetic particles. These results are important for understanding the effects of nanosized grains on the magnetic properties and features of magnetization of the Sr2FeMoO6–δ polydisperse powder, a promising material for spintronic device applications.

Microstructure and magnetic properties of FeAs with coarse-grain and nanocrystalline structure

The microstructure and magnetic properties of iron arsenide (FeAs) with coarse-grain and nanocrystalline structure were investigated. Coarse-grain FeAs was synthesized through high-energy ball milling and heat treatment. Nanocrystalline FeAs was obtained by ball milling of coarse-grain FeAs. The results suggest that the reduced grain size of FeAs (from >100 to 32.4 nm) is accompanied by the introduction of internal strains up to 0.568% with ball milling time from 0 to 32 h. The magnetic properties of FeAs show that the coercivity is reduced from 29.2 to 15.6 kA/m and the magnetization is increased over time of milling. The low coercivity is mainly due to the small grain size stemmed from ball milling, while the increase of magnetization is primarily caused by the change of lattice parameters of FeAs and the emergence of superparamagnetic phase at the same time.

Characterization and Mössbauer spectroscopy of steel slag generated in the ladle furnance in SIDERPERU steel plant

The steel industry produces large amounts of slag coming from different stages during the steelmaking process every year. Currently, there are numerous attempts to recycle it or to use it in some other industry sectors and to preserve the environment. The characteristics of the slag depends on the steelmaking process and it is crucial to have it before any attempt of recycling. In this work, slag sample produced in the ladle furnace from SIDERPERU steel plant were collected and analyzed by using energy dispersion X-ray (EDX), X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), SQUID magnetometer and Mössbauer spectroscopy. The chemical analysis obtained by EDX and XRF indicate that the main elemental composition of the material is Fe, Ca, Si and Cr. XRD identifies that these elements are in the phases: FeO, Fe3O4, α-Fe2O3, Ca2SiO4, and Ca2,32Mn0,68SiO7. Magnetometry measurements suggest the Verwey transition for magnetite and the Morin transition for hematite are screened by the presence of superparamagnetic phases. The Mössbauer spectrum shows two doublets related to Fe2+ and Fe3+ ions with hyperfine parameters belonging to that of non-stoichiometric wustite. Also, the presence of hyperfine fields characteristic of the Fe3O4 and Fe2O3 phase identified at room temperature verifies the magnetometry analysis. The analysis of the sample used in this work reveals details connected with the steel fabrication processes and are helpful for posterior recycling attempts.

Магнитные наночастицы Zn-=SUB=-x-=/SUB=-Fe-=SUB=-3-x-=/SUB=-O-=SUB=-4-=/SUB=- (0 ≤ x≤ 1.0), функционализированные полиакриловой кислотой (Zn-=SUB=-x-=/SUB=-Fe-=SUB=-3-x-=/SUB=-O-=SUB=-4-=/SUB=-@ПАК)

Studies of the properties of ZnxFe3-xO4 (x=0, 0,25, 0,5, 0,75, 1) magnetic nanoparticles synthesized by a modified hydrothermal method are presented in comparison with the properties of the same nanoparticles stabilized with polyacrylic acid ZnxFe3-xO4@PAA. The structure, size, morphology, and magnetic properties of the samples were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT IR), physical properties measurements (PPMS), and Mossbauer spectroscopy. The synthesized nanoparticles are single-phase, without additional impurities, have a narrow size distribution and are in the superparamagnetic phase. From the RD measurements, it was found that with an increase in the Zn content from x = 0 to x= 1.0, the sizes of nanoparticles increasing from 17 to 33 nm. Analysis of the Mössbauer spectroscopy data showed that when doped with Zn ions from x=0 to x=1.0, the sizes of nanoparticles decreasing from 15 nm to 5 nm. The results of the Mossbauer studies showed that both ZnxFe3-xO4 and ZnxFe3-xO4@PAC has a core/shell type structure in which the core is magnetically ordered, whereas the shell does not have magnetic ordering. Mossbauer studies indicate that the coating of citric acid particles leads to their isolation from each other, a decrease or elimination of interactions between particles, a decrease in the thickness of the paramagnetic shell, and, due to this, an increase in the diameter of the core.

Zn-=SUB=-x-=/SUB=-Fe-=SUB=-3-x-=/SUB=-O-=SUB=-4-=/SUB=- (0 ≤ x≤ 1.0) magnetic nanoparticles functionalized with polyacrylic acid (PAA)

Studies of the properties of ZnxFe3-xO4 (x=0, 0.25, 0.5, 0.75, 1.0) magnetic nanoparticles synthesized by a modified hydrothermal method are presented in comparison with the properties of the same nanoparticles stabilized with polyacrylic acid ZnxFe3-xO4@PAA. The structure, size, morphology, and magnetic properties of the samples were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT IR), physical properties measurements (PPMS), and Mossbauer spectroscopy. The synthesized nanoparticles are single-phase, without additional impurities, have a narrow size distribution and are in the superparamagnetic phase. From the (XRD) measurements, it was found that with an increase in the Zn content from x=0 to x=1.0, the sizes of the nanoparticles were increasing from 17 to 33 nm. Analysis of the Mossbauer spectroscopy data showed that when doped with Zn ions from x=0 to x=1.0, the sizes of the nanoparticles were decreasing from 15 nm to 5 nm. The results of the Mossbauer studies showed that both ZnxFe3-xO4 and ZnxFe3-xO4@PAA has a core/shell type structure in which the core is magnetically ordered, whereas the shell does not have magnetic ordering. Mossbauer studies indicate that the coating of citric acid particles leads to their isolation from each other (i. e., a decrease in the thickness of the paramagnetic shell, and due to this to increasing in the diameter of the core). This (the last sentense) sentense is too long. It could be mode two or three sentences for better clarification. Keywords: ferrite-spinel nanoparticles, hydrothermal synthesis, polyacrylic acid functionalization, Mossbauer spectroscopy, properties, crystal and magnetic structure.

Magnetic nanoparticle-based solid phase peptide synthesis and the synchronous detection of their biological activity

The solid-phase peptide synthesis (SPPS) strategy, as the main procedure of peptide manufacturing, has a profound impact on the research of peptides. The rapid development of nanotechnology is expected to promote the evolution of the solid phase to miniaturization, convenience and multi-function. In this work, silica-coated magnetic ferriferous oxide (Fe3O4) nanoparticles (MNP/SiO2) were used as new generation of solid phase for SPPS in Fmoc chemistry. The superparamagnetic solid phase facilitated a multi-step synthesis reaction due to its magnetic maneuverability, which could efficiently separate reaction intermediates, and were then redispersed in the next-step synthetic solution for peptide elongation. In addition, this strategy further allowed the simultaneous acquisition of magnetic nanoparticle–peptide conjugates as available bioprobes to examine the biological function of synthesized peptides. The feasibility of this novel magnetic nanoparticle-based solid phase peptide synthesis (MNP-SPPS) strategy was confirmed by the synthesis of arginine-glycine-aspartic acid-glycine-glycine (RGDGG) as a model pentapeptide. The simultaneously acquired magnetic nanoparticle–peptide conjugates (RGDGG-MNP/SiO2), possessing excellent biological functions, could be recognized and further internalized by tumor cells through receptor-mediated endocytosis, thereby achieving the extraction and removal of malignant cells in vitro under an external magnetic field. The RGDGG-MNP/SiO2 could further be used as a contrasting agent for tumor-targeting T2 magnetic resonance imaging in vivo. This study developed a novel MNP-SPPS strategy that could realize the simple synthesis of peptides, and the synchronously obtained nanoprobes could quickly detect the biological activity of the target synthetic sequence. This strategy may have broad application prospects in combinatorial chemistry and the construction of peptide libraries in the future.

Nanocomposite Obtained in the Plasma of a Pulsed High Voltage Discharge Using Nickel Electrodes and PTFE

In the plasma of pulsed high-voltage discharge, initiated between nickel electrodes in air, when the fluoroplastic is placed in the discharge gap, powder nanocomposite material has been synthesized. The nanocomposite contains NiF2 nanoparticles less than 5 nm in size, dispersed in a matrix consisting of carbon and fluorocarbon substances. The carbonaceous substance contains nanoscale disordered graphite-like regions. The fluorocarbon component of the composite contains fragments of PTFE molecules and fluorocarbon molecular fragments that differ in structure from PTFE molecule’s structure. After annealing the composite in air at 773 K, the initial nanocomposite is transformed into a nanocomposite containing nanosized PTFE and nanoparticles of NiF2 less than 5 nm in size, scattered in a matrix composed of nanographite and low-layer nanosized graphene, after aneling at 1173 K into a material containing NiO nanoparticles less than 10 nm in size. After annealing of the initial nanocomposite in argon atmosphere at 1073 K, the obtained nanocomposite contains Ni nanoparticles with sizes less than 5 nm and carbon and fluorocarbon components. The magnetic susceptibility of the unannealed nanocomposite is investigated. A transition to the antiferromagnetic phase at 73 K was detected. At T = 4K, exchange bias interaction of the AFM / FM type takes place in the composite. There is divergence of the FC and ZFC curves, which can be explained by the presence of a superparamagnetic phase or a spin glass phase in the sample. The field dependences of the magnetic susceptibility measured at T = 300 K show sharp changes that occur at certain values of the magnetic field. Elucidation of the nature of these changes requires additional research.

Investigation of the magnetocaloric effect and the critical behavior of the interacting superparamagnetic nanoparticles of La0.8Sr0.15Na0.05MnO3

We report on structural, magnetic properties of Na-doped La0.8Sr0.15Na0.05MnO3 (LSNMO) nanoparticles (NP) with size about 50 nm elaborated via sol-gel route. The chemical composition was verified using the energy dispersive X-ray analysis (EDAX) and by X-ray photoelectron spectroscopy (XPS). Magnetic characterizations demonstrate that LSMNO exhibits a coexistence of interacting superparamagnetic (ISPM) phase with blocking temperature TB = 194 K and a ferromagnetic phase with Curie temperature TC = 255.5 K. At low temperatures, the SPM state undergoes a collective freezing state at Tf = 46 K. the high-temperature regime (well above TC) reveals that NP-LSNMO has a strengthened Griffiths-like phase compared to their bulk counterpart. An itemized investigation of the critical behavior of the material was carried out in the vicinity of TC. The critical exponents [β = 0.546(7), γ = 0.972(6), and δ = 2.94 (5)] were found to be in close agreement with of the mean-field theory. The maximum magnetic entropy change (−ΔSMpk) is about 1.41 Jkg-1 K-1 and the refrigeration capacity (RC) is 288 Jkg-1 for a field change of 5 T at T = 215 K. This magnetocaloric response is reasonably high for nanomaterials and, together with its cost-effectiveness, makes NP LSMNO a potential candidate material for active magnetic refrigerators. Besides, the ISPM properties are desirable for hyperthermia applications. Our findings suggest that the magnetic inhomogeneity and the dipolar interaction between the SPM and FM phases in the range TB<T<TC are crucial factors in determining the magnetic properties of NP-LSNMO.

Tailored Synthesis of Iron Oxide Nanocrystals for Formation of Cuboid Mesocrystals.

In this work, we systematically studied the shape- and size-controlled monodisperse synthesis of iron oxide nanocrystals (IONCs) for their use as building blocks in the formation of mesocrystals. For this aim, on understanding the influence of the oleic acid concentration, iron-oleate concentration, and heating rate on the synthesis of robust and reproducible IONCs with desired sizes and shapes, we synthesized highly monodisperse ∼11 nm sized nanocubes and nanospheres. Magnetic measurements of both cubic and spherical IONCs revealed the presence of mixed paramagnetic and superparamagnetic phases in these nanocrystals. Moreover, we observed that the magnetic moments of the nanocubes are more substantial compared to their spherical counterparts. We then demonstrated a simple magnetic-field-assisted assembly of nanocubes into three-dimensional (3D) cuboid mesocrystals while nanospheres did not form any mesocrystals. These findings indicate that small cubic nanocrystals hold great promise as potential building blocks of 3D magnetic hierarchical structures with their superior magnetic properties and mesocrystal assembly capability, which may have high relevance in various fields ranging from high-density data storage to biomedical applications.

High magnetic fluid hyperthermia efficiency in copper ferrite nanoparticles prepared by solvothermal and hydrothermal methods

CuFe2O4 magnetic nanoparticles (MNPs) of two different morphologies and high magnetic heating efficiency are prepared using hydrothermal (CF) and solvothermal (CFPG) methods. Temperature dependent magnetization measurements indicate the presence of superparamagnetic phase at room temperature. The saturation magnetization for CFPG MNPs (~32.7 emu/g) is found to be ~ 31% higher than the CF MNPs, which is due to nearly collinear Neel type alignment of the magnetic moments in the tetrahedral and octahedral sites with a low Yafet-Kittel angle of ~ 5.980 and lower thickness of the magnetically disordered shell, which are confirmed from the cation distributions, non-zero spin canting angles and sub-spectral area analyses using low temperature (~5 K) in-field (~5 T) Mössbauer spectroscopy. The maximum specific absorption rate for CFPG MNPs is found to be ~ 192 ± 7 W/g, which is significantly higher than the previously reported values for copper ferrite MNPs. The high heating efficiency of CFPG MNPs is attributed to the near-resonant relaxation dynamics (ωτ ~ 1, where ω and τ indicate the angular frequency of the applied field and effective relaxation time, respectively). Heating efficiency is found to decrease with increasing sample concentration due to an enhancement in dipolar interactions, which is found to be in agreement with the quasi-static calculations. In vitro cytotoxicity studies indicate good bio-compatibility of the CFPG MNPs against human colon epithelial cells (HT-29) due to the presence of polyethylene glycol coating. The observed high heating efficiency along with negligible room temperature coercivity and superior bio-compatibility indicate the suitability of the solvothermally synthesized CuFe2O4 MNPs for magnetic fluid hyperthermia.

Tricritical Phenomena and Cascades of Temperature Phase Transitions in a Ferromagnetic Liquid Crystal Suspension

We consider temperature-driven phase transitions occurring in a liquid crystal suspension of ferromagnetic particles within the Landau–de Gennes theory. The temperature dependences of the order parameters in the uniaxial model with a vector order parameter for the magnetic subsystem are obtained. The dimensionless expression for the free energy density of the suspension has been used for the study of the phase behavior general regularities of the system. Phase state diagrams of the suspension and temperature dependences of the order parameters of the liquid crystal and the ensemble of magnetic particles for different values of the phenomenological expansion coefficients are constructed. It is shown that the considered model admits the existence of a cascade of temperature phase transitions: isotropic phase–superparamagnetic nematic phase–ferromagnetic nematic phase. We have shown that in the mesomorphic state of the liquid crystal, the spontaneous magnetization can appear in a continuous way or by a jump with decreasing temperature, which corresponds to the tricritical behavior. The values of temperature and expansion coefficients corresponding to the tricritical and triple points are numerically found.

Evidence of magnetic dilution due to unusual occupancy of zinc on B-site in NiFe2O4 spinel nano-ferrite

The present article investigates the influence of Zn substitution on magnetic properties of Ni1−xZnxFe2O4 spinel nano ferrite compounds. The materials were prepared via sol-gel auto combustion method followed by suitable sintering. X-ray powder diffraction pattern shows formation of cubic nanostructure for all values of ‘x’. The magnetic measurement at room temperature shows the narrow M ​− ​H curve indicating the superparamagnetic behavior. Unlike normal tetrahedral occupancy of Zn ions in bulk ferrite, the Zn ions peculiarly preferred octahedral sites and led to dilute magnetization in prepared nano ferrite. The nano ferrite shows small value of saturation magnetization and coercivity. Mössbauer spectra were studied at room temperature which also confirms the existence of superparamagnetic phase in nano ferrites and well supports the fact that Zn replaces the Fe ions at the octahedral site. The substitution of Zn ions gives paramagnetic doublet and lead to weakening the magnetic interaction and decrease hyperfine field at A and B sites. The study also explains the effect of Zn substitution on Bohr's magneton, Yafet–Kittel angle, coercivity (Hc), remnant magnetization, magnetic susceptibility and Curie temperature.