Improved Saturation Magnetization Research Articles

Effect of element infiltration on radial composition/structure and magnetic/electrical properties of Fe-B amorphous powders prepared by spark erosion

Before confirming spark erosion as an effective technique for producing Fe-based amorphous powders, it is crucial to thoroughly investigate their magnetic/electrical properties and the impact of different elements infiltration on composition, microstructure, and performances. Limited research has been conducted on the magnetic and electrical properties of spark-eroded Fe-based amorphous powders, and there is a dearth of studies on the influence of different elements' infiltration. In this work, a series of binary Fe83B17 amorphous powders were synthesized using water (as a source of O), ethanol (as a source of C and O), and silicone oil (as a source of O, Si, and C). The elements O, C, and Si exhibit different concentration distributions along the radial direction in the synthesized powders. The depth of O infiltration varies between 10 and 35 nm, C from 190 to 280 nm, and Si barely diffuses inward. For powders prepared in water (WF), the formation of nanoclusters throughout the particle leads to an improved saturation magnetization. Besides, the infiltrated mass ratio of O is merely 1.38 wt% and is predominantly concentrated in the surface of WF powder, resulting in a significant increase in resistivity. The resistivity of WF powder is approximately four orders of magnitude higher compared to powders prepared in ethanol (EF) and silicone oil (SF). Nanoclusters are also observed in EF and SF powders, where the significant infiltration of non-magnetic C leading to a reduction in the saturation magnetization of both EF and SF powders. Inside EF powder, a remarkable peak of C content appears at ∼30 nm away from the powder surface in the radial direction, accompanied by an increase in structural order. This suggests a synchronous relationship between the variations of structural order in the radial direction and the concentration of the infiltration element. These findings demonstrate the practical feasibility of tuning composition and microstructure via dielectrics to develop high-performance Fe-based amorphous powders.

Eco-friendly synthesis of fluorescent cobalt-doped manganese ferrites for thermo-therapeutic applications

The synthesis of high-quality nanoparticles for biomedical applications through environmentally friendly methods is a major challenging task. In this work, oxidative precipitation and a novel method, oxidative hydrothermal synthesis, are explored as one-pot eco-friendly synthesis routes to obtain single phase multicore-like and single-core citrate-stabilized cobalt and/or manganese-doped ferrite (CoxMn1-xFe2O4, 0 ≤ x ≤ 1) nanoparticles, respectively. The Co2+/Mn2+ ratio and synthesis method were found to influence the nanoparticles' morphology and structure, with oxidative precipitation producing multicore-like structures and hydrothermal synthesis yielding single-core particles with crystalline sizes in the range of 2 − 10 nm and 4 − 11 nm, respectively. Inductively coupled plasma optical emission spectrometry (ICP-OES) indicated a composition near the expected values. Mixed ferrites displayed improved saturation magnetization up to 60 A.m2/kg, exhibiting superparamagnetism at room temperature. The particles’ stability was evaluated in physiological pH, and the mixed ferrites displayed intrinsic fluorescence emission in the violet-green range with a maximum wavelength near 425 nm. The cobalt and/or manganese-doped ferrites were evaluated for magnetic hyperthermia and photothermia, displaying high heating efficiency for several alternating magnetic field conditions (up to ∼2.5 nHm2/kg) compatible with biological applications, and high light-to-heat conversion efficiency (up to ∼53%) with near infrared (NIR) laser irradiation at 808 nm. Hereby, the oxidative precipitation and oxidative hydrothermal synthesis are promising eco-friendly methods for the development of crystalline citrate-stabilized cobalt and/or manganese-doped ferrites with multicore-like and single-core spherical morphology, respectively, without requiring additional post-synthesis treatments and with suitable properties for biomedical applications, such as magnetic hyperthermia, photothermia and as prospective fluorescent probes for bio-imaging.

Efficient energy and memory storage capabilities in optimized BiFeO3/MnMoO4/NiFe2O4 triphasic composites for futuristic multistate devices.

The emergence of multiferroic materials particularly bismuth iron oxide (BiFeO3) with distinctive magnetoelectric, and high energy storage capabilities, present pivotal aspects for next-generation memory storage devices. However, intrinsically weak magnetoelectric coupling limits their widespread applications, that can be leap over by the integration of BiFeO3 with enriched ferroelectric, and ferro/ferrimagnetic materials. Here, a series (1 - x)[0.7BiFeO3 + 0.3MnMoO4] + xNiFe2O4 (x = 0.00, 0.03, 0.06, and 0.09) is synthesized via citrate-gel based self-ignition, and solid-state reaction routes. Phase purity and crystallinity of tri-phase composites with surfaces revealing random and arbitrarily shaped grains are assured by X-ray diffraction, and field emission scanning electron microscopy, respectively. Dielectric studies illustrated non-linear trend for broad range of frequencies as predicted by Maxwell-Wagner theory along with single semicircle arcs in Nyquist plots that exposes grain boundaries effect. An enriched 68.42% of ferroelectric efficiency is featured for x = 0.06 substitutional contents, while magnetic computations demonstrated improved saturation magnetization (M s), remanence magnetization (M r), and coercive applied magnetic field (H c) values as 5.87 emu g-1, 0.96 emu g-1, and 215.19 Oe, respectively for x = 0.09 phase-fraction. The intriguing linear trends of magnetoelectric coupling for all the compositions are corroborating them propitious contenders for futuristic multistate devices.

A threefold increase in SAR performance for magnetic hyperthermia by compositional tuning in zinc-substituted iron oxide superparamagnetic nanoparticles with superior biocompatibility

In this work, we report a ultrahigh specific absorption rate (SAR) performance in Zn-substituted magnetite superparamagnetic (SPM) nanoparticles (NPs) for potential application in magnetic hyperthermia (MHT)-based cancer treatment. Although MHT shows promise in cancer therapy, challenges such as low heating performance, agglomeration of magnetic nanoparticles (MNPs) in blood veins, cytotoxicity, and hemocompatibility have hindered clinical uses. To overcome these challenges, we adopted a reverse-micelles based coprecipitation synthesis approach to prevent MNPs agglomeration and optimized the substitution of Zn ions in magnetite to enhance heating performance. Calorimetric measurements showed SAR values of 118 W/g and 181 W/g for magnetite NPs using the initial slope method (ISM) and Box Lucas method (BLM), respectively. Through our compositional optimizations, we achieved a significant increase in SAR value by consciously substituting Zn2+ ions in the magnetite lattice. Specifically, we obtained SAR values of 325 W/g and 579 W/g (>300% increase) for Zn0.3Fe2.7O4 MNPs using ISM and BLM, respectively. This enhancement can be attributed to improved saturation magnetization (174–257 kA/m) and magneto-crystalline anisotropy (12–24 kJ/m3). The increase in saturation magnetization in the magnetite MNPs can be explained by the higher magnetic moment resulting from increased Zn concentration up to ZnxFe3-xO4(x = 0.3), strengthening the JAB interaction. However, further increases in Zn concentration lead to a decrease in saturation magnetization due to non-collinearity, as described by the Yafet-Kittle model. Our optimized MNPs exhibit improved heating performance, enabling the use of lower MNPs concentrations for cancer treatment, reducing potential toxicity effects. Biocompatibility investigations demonstrated a low hemolysis rate (<5%) in a hemolysis assay with red blood cells and high cytocompatibility (>92% cell viability) in MTT assays for all compositions, confirming their potential suitability for clinical applications. This study offers a promising approach to enhance SAR performance, addressing MHT-based cancer treatment challenges, and improving clinical suitability.

Flash sintering improves magnetic properties of spinel zinc ferrite

We report on a simple protocol for one step synthesis and sintering of single-phase magnetic spinel ZnFe2O4 zinc ferrite (ZFO) using an electric field assisted sintering. The resultant materials show improved saturation magnetization and higher coercivity compared to conventionally sintered ferrite. The changes in properties have been attributed to generation of non-thermal lattice defects when processed under electric field. Instead of using the high temperatures (>1000 °C) and extended dwell periods (> 4 h) required by the traditional sintering processes, this method permits sintering of ZFO at a furnace temperature of only 950 °C in just a minute by applying a minimal field of 25 Vcm−1. This magnetic material with decreased coercivity and increased saturation magnetization will improve the efficiency of solenoids, transformer/inductor cores, microwave devices and magnetic shields.

Strong magnetoelastic coupling in MnCoSi compounds studied in pulsed magnetic fields

The orthorhombic MnCoSi compounds have been found to present a large magnetoelastic coupling, which is regarded as the source for the magnetocaloric effect (MCE) and the magnetostrictive effect. As a result, these compounds are potential materials for caloric applications such as solid-state refrigeration. In the present study, we offer fundamental insights in the magnetoelastic coupling in these compounds based on their structural, metamagnetic, and MCE behavior. The directly measured adiabatic temperature change ($\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}$) in different initial temperatures (down to 18 K) and pulsed magnetic fields (up to 40 T) presents a moderate MCE performance (the maximum $\mathrm{\ensuremath{\Delta}}{T}_{\mathrm{ad}}=--3.1\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for a field change of 13 T), which results from the metamagnetic behavior of these compounds. Furthermore, the magnetization measurements in pulsed (and static) magnetic fields indicate that the magnetoelastic coupling is significantly enhanced for increasing fields resulting in an improved saturation magnetization. The metamagnetic transition is continuously pushed to lower temperatures in higher fields. The phase diagram constructed from the experimental transition temperatures ${T}_{t}$ and the critical magnetic fields ${\ensuremath{\mu}}_{0}{H}_{\mathrm{cr}}$ indicate that the transition is terminated below 18 K and that ferromagnetism is stabilized for fields above 22.3 T. Our results provide unique insights into the strong magnetoelastic coupling under high pulsed magnetic fields, providing guidelines for the design of giant magnetocaloric materials for future caloric applications.

Magnetic and mechanical properties of additively manufactured Alx(CoFeNi) complex concentrated alloys

Varying the Al content, strongly influences the microstructure, magnetic and microhardness of additively manufactured Alx(CoFeNi) (x = 0, 10, 30) complex concentrated alloys (CCA). Compared to the single FCC phase of CoFeNi, the hierarchical FCC/L12+BCC/B2 heterostructure of heat treated Al10(CoFeNi) CCA displayed substantially improved saturation magnetization, Curie temperature and microhardness. However, there was no significant change in the properties of heat treated CoFeNi and Al30(CoFeNi) CCA. These findings can be rationalized via thermodynamic modelling of the phase stability. We have demonstrated the feasibility of exploiting additive manufacturing for rapidly screening and developing novel high-performance alloys for next generation rotating electrical machines.

Biocompatible Tb doped Fe3O4 nanoparticles with enhanced heating efficiency for magnetic hyperthermia application

Magnetic hyperthermia has a specific limitation in treating localized and relatively accessible malignant tumors regardless of its promising therapeutic regime. In this present work, Tb doped Fe3O4 magnetic nanoparticles (MNPs) prepared via coprecipitation root and confirmed the structural conformation and phase purity by XRD, FTIR, TEM, and SEM analysis. TGA analysis was carried out for thermal stabilization and to verify the formation of a stable phase. The occupancy of Tb ions at the octahedral sites and cationic distribution can be calculated from Rietveld refinement analysis. The relaxation mechanism, dipolar- dipolar interactions among the particles, and randomly directed magnetic anisotropy axes were investigated by ESR spectroscopy. The magnetic results enumerate that increasing Tb doping concentration leads to increased saturation magnetization and decreased coercivity and retentivity. The self-heating properties of the doped nanoparticles were characterized by measuring specific absorption rate (SAR). The improved saturation magnetization and enriched SAR value enable the doped MNPs for magnetic hyperthermia application with excellent efficacy.

Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 (BITCx/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co2+ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITCx/LSMO composite thin films was investigated. Co2+ doping induces improved ferroelectricity and weak ferromagnetism for the BITCx phase. Especially, the single-phase BITC0.05 film exhibits a maximum ME voltage coefficient (αE) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ϵr, minimum tanδ, highest remnant polarization of 24.2 μC/cm2, lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum aE value of 27.3 V/cm·Oe. Based on these findings, Co2+-doped Bi4Ti3O12 has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi4Ti3O12 with ferromagnetic oxides benefits the improvement of ME composite thin films.

The improved saturation magnetization and initial permeability in Mn–NiZn ferrites after cooling in vacuum

The improved saturation magnetization and initial permeability in Mn–NiZn ferrites after cooling in vacuum

Sonochemical synthesis of MnFe2O4 nanoparticles with ionic liquid and their application in magnetic and dielectric polystyrene nanocomposites

Abstract MnFe2O4 nanoparticles were successfully synthesized via a simple sonochemical reaction by using 1-butyl-3-methylimidazolium bromide ionic liquid and cetyl trimethylammonium bromide as surfactant. MnFe2O4 nanoparticles with ionic liquid were added to polystyrene for preparation of magnetic polymeric nanocomposites. Structural, morphological, spectroscopic, magnetic and dielectric properties were investigated by means of transmission electron microscopy, X-ray powder diffractometry, Fourier transform infrared spectroscopy and vibrating sample magnetometry respectively. The results of thermogravimetric analysis indicated that the addition of MnFe2O4 nanoparticles with ionic liquid to polystyrene improved the thermal stability of the nanocomposite. The magnetization curves elucidate that the MnFe2O4 nanoparticles with ionic liquid/polystyrene nanocomposite has ferromagnetic behavior and improved saturation magnetization, coercivity and remanent magnetization. The electrical quantities such as dielectric constant (ε′), imaginary permittivity (ε″) and dielectric loss (tan (δ) = ε″/ε′) of MnFe2O4 nanoparticles and MnFe2O4 nanoparticles with ionic liquid/polystyrene nanocomposite were evaluated for temperature and frequency dependence. The obtained results are enhanced due to increase in the temperature and decreased with increasing frequency in MnFe2O4 nanoparticles with ionic liquid/polystyrene nanocomposite.

Fabrication, structural and magnetic behavior of novel one-dimensional Fe2MnGa nanostructures

Well aligned Fe2MnGa nanowires (NWs) have been synthesized through low cost and versatile electrochemical deposition technique with constant stirring during the growth process in anodic aluminum oxide (AAO) templates. The average diameter is 50 nm and the lengths up to a few micrometers have been confirmed through morphological analysis. The NWs are found to be in body centered cubic structure with (220) preferred orientation. The magnetic behavior has been investigated at room temperature (RT) as well as at low temperatures. The dominant shape anisotropy compelled the preferable magnetization axis to be in axial direction of NWs. Angular dependence of coercivity shows coherent rotation of magnetic domain on reversal of external magnetic field due to the stronger interwire couplings. At lower temperatures, superparamagnetic contributions from very small nanoparticles in blocking state significantly improved saturation magnetization (Ms) from 0.101 to 0.205 emu and coercivity from 1354 to 1632 Oe. A mixed behavior of exchange bias has been manifested by the NWs at lower temperatures owing to the rearrangement of atoms between the interface of antiferromagnetic and ferromagnetic grains. This causes significant disturbance for pining effect resulting fluctuating exchange bias phenomenon.

Pseudo single domain NiZn-γFe2O3 colloidal superparamagnetic nanoparticles for MRI-guided hyperthermia application

Magnetic resonance imaging (MRI)-guided magnetic nanofluid hyperthermia (MNFH) is highly desirable in cancer treatment because it can allow for diagnosis, therapeutics, and prognosis simultaneously. However, the application of currently developed iron-oxide based superparamagnetic nanoparticles (IOSPNPs) for an MRI-guided MNFH agent is technically limited by the low AC heat induction power at the physiologically tolerable range of AC magnetic field (H AC,safe), and the low transverse r 2-relaxivity responsible for the insufficient heating of cancers, and the low resolution of contrast imaging, respectively. Here, pseudo single domain colloidal Ni x Zn1−x –γFe2O3 (x = 0.6) superparamagnetic nanoparticle (NiZn-γFe2O3 PSD-SPNP) physically and theoretically designed at the H AC,safe, specifically by the applied frequency, is proposed for a highly enhanced MRI-guided MNFH agent application. The NiZn-γFe2O3 PSD-SPNP showed the superparamagnetic characteristics, significantly enhanced AC heat induction performance (ILP = 6.3 nHm2 kg−1), highly improved saturation magnetization (M s = 97 emu g−1 Fe, 3.55 × 105 A m−1) and r 2-relaxivity (r 2 = 396 mM−1 s−1) that are desirable for highly efficient MRI-guided MNFH agent applications. According to the analyzed results, the remarkably enhanced effective relaxation time constant and its dependent out-of-phase magnetic susceptibility, as well as the DC/AC magnetic softness optimized by the PSD-SPNP at the H AC,safe were revealed as the main physical reason for the significance. All the fundamental in vitro and in vivo experimental results demonstrated that the physically designed NiZn-γFe2O3 PSD-SPNP is bio-technically feasible for a highly efficient MRI-guided MNFH agent for future cancer nanomedicine.

Co–Al-substituted strontium hexaferrite for rare earth free permanent magnet and microwave absorber application

Permanent magnets (PMs) have tremendous demand because of their applicability in various electronic devices. Rare earth (RE) elements are the major component in fabricating these PMs. Tremendous research interest has been generated over the last decade to design the RE-free PMs because of the ever-increasing cost of REs and shortage of their supply. Hexagonal ferrites show incredible potential as RE-free magnets owing to their high coercivity and moderate saturation magnetization. In this work, we focused on improving the magnetic properties of Sr0.8Ca0.2AlxCoxFe12−2xO19 hexagonal ferrites with respect to Co2+–Al3+ co-substitution synthesized by the sonochemical method. Improved saturation magnetization of 64.4 emu g−1, coercivity of 13.2 kOe, and a remnant ratio of 0.71 was achieved upon Co2+–Al3+ substitution. The prepared materials were also tested for microwave absorption characteristics, where a maximum reflection loss of −35.4 dB at 12.36 GHz was obtained. Results were discussed in light of the synthesis method, Co2+–Al3+ substitution, and electrical properties. Such improvement in the electromagnetic properties make these ferrites suitable for use as RE-free PMs and microwave absorbers.

Co-Doped Rare-Earth (La, Pr) and Co-Al Substituted M-Type Strontium Hexaferrite: Structural, Magnetic, and Mossbauer Spectroscopy Study

The present study investigates the influence of La3+ and Pr3+ doping on the structural, magnetic properties, and hyperfine fields of Sr0.7RE0.3Fe12-2x CoxAlxO19, (RE: La3+ and Pr3+, x = 0.0 - 0.8) hexaferrite compounds prepared via auto-combustion technique. The XRD analysis shows a linear decrease in a and c lattice and unit cell volume contraction with the content x. The room temperature magnetic study shows that for the Pr3+ doped Sr0.7Pr0.3Fe12-2x CoxAlxO19 (Pr3+-SrM), the magnetization value monotonically decreases while for La3+ doped Sr0.7La0.3Fe12-2xCoxAlxO19 (La3+-SrM) magnetization value shows a noticeable increase in magnetization value with x. The coercivity of the Pr3+-SrM compound was observed to decrease while that of the La3+-SrM compound showed a marked 40% increase at x = 0.2 (~5829 Oe) in comparison to undoped SrFe12O19 (~3918 Oe). A difference in Curie temperature was also observed, with Tc ~ 525°C at x = 0.4 for Pr3+-SrM and Tc = 505°C for x = 0.4 for La3+-SrM compound. The observed differences in magnetic properties have been explained on the basis of the site occupancy of Co2+ and Al3+ in the presence of rare-earth ions. The presence of non-magnetic rare-earth ion, La3+, improved saturation magnetization, and coercivity and deemed suitable replacement for Sr2+. The hyperfine parameters namely quadrupole shift showed a decrease with the La3+ or Pr3+ doping independent of (Co2+-Al3+) ions doping. Overall, the Mossbauer analysis suggests that the (Co2+-Al3+) impurities prefer occupancy at 2a site.

Orientation-modulated multiferroic properties of BCZT/LCMO bilayer heterostructures

In this paper, orientation-modulated multiferroic properties of Ba0.85Ca0.15Zr0.1Ti0.9O3/La0.67Ca0.33MnO3 (BCZT/LCMO) bilayer heterostructures grown on (001), (110), and (111)-oriented Nb-doped SrTiO3 single-crystal substrates are investigated. Epitaxially grown heterostructures with sharp and clear interfaces are verified by TEM analysis. Results show the strong orientation dependence of multiferroic properties for the heterostructures. The optimal ferroelectric and dielectric properties lie in the (001) direction, whereas the improved saturation magnetization and piezoelectric response are achieved in (111)-oriented heterostructure. The maximum magnetoelectric coupling is obtained in (111)-oriented heterostructure with a αE31 value of 207 mV/cm·Oe.

Evidence of various stabilizing mechanisms in ferromagnetic Co doped ZnO nanocrystals

In spite of the extensive investigations on Co-doped ZnO, existence as well as origin of ferromagnetism remains controversial. Role of charge carriers and defects on the ferromagnetic ordering of Al, Co-codoped ZnO nanocrystals (NCs) having size as small as 5.5 nm is evaluated on the basis of optical spectroscopy, electron spin resonance and Raman spectroscopy. Al, Co-codoped ZnO NCs reveal improved saturation magnetization in a subtle way. Concomitant increase in the charge carriers is vivid from the optical absorption spectra of colloidal codoped NCs. The doping level is maintained low enough so that NCs are free of any secondary or impurity phase. Shape of the M(T) curves is analyzed to elucidate exchange interaction in doped ZnO NCs. The present experimental work indicates that the multiple mechanisms are responsible for stabilizing the ferromagnetic ordering in Co-doped ZnO NCs; thereby controversial reports are published in the literature.

Synthesis and Characterization of MnZn Ferrite Nanoparticles with Improved Saturation Magnetization

Mn0.8Zn0.2Fe2O4 nanoparticles with improved saturation magnetization were prepared by a modified hydrothermal method. This method involves a chemical co-precipitation of hydroxides under a vacuum condition using potassium hydroxide as a precipitating agent, followed by a separate hydrothermal process. To understand the advantages of the modified hydrothermal method proposed above, a sample having identical stoichiometry was prepared by conventional hydrothermal method, during which the preparation of precursor was conducted in an open system. The samples were characterized by XRD, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and TEM. The magnetic property was tested by vibrating sample magnetometer (VSM). XPS results show that the Mn cations of the nanoparticles prepared by modified hydrothermal method have lower average valence. The MnZn ferrite nanoparticles prepared by modified hydrothermal method have smaller diameter (16.1 nm, calculated by XRD) and higher room temperature saturation magnetization, 80 emu/g, which is even better than the reported value. The saturation magnetization of the particles prepared by modified hydrothermal method is 1.6 times of the particles prepared by conventional hydrothermal method.

Preparation of Magnetic Iron Oxide Nanoparticles (MIONs) with Improved Saturation Magnetization Using Multifunctional Polymer Ligand.

This paper describes the preparation of ultra-small magnetic iron oxide (Fe3O4) nanoparticles (MIONs) coated with water-soluble thioether end-functionalized polymer ligand pentaerythritol tetrakis 3-mercaptopropionate-polymethacrylic acid (PTMP-PMAA). The MIONs were prepared by co-precipitation of aqueous iron precursor solution at a high temperature. The polymer modified MIONs were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), and vibrating sample magnetometery (VSM). It was found that these MIONs were successfully modified by this water-soluble polymer ligand with a fairly uniform size and narrow size distribution. The dried powder of MIONs could be stored for a long time and re-dispersed well in water without any significant change. Additionally, the polymer concentration showed a significant effect on size and magnetic properties of the MIONs. The saturation magnetization was increased by optimizing the polymer concentration. Furthermore, the 3-(4,5-dimethylthiazol-2-yl)-2-5-diphenyltetrazolium bromide (MTT)-assay demonstrated that these MIONs were highly biocompatible and they could be successfully coupled with fluorescent dye Rhodamine due to the formation of amide bond between carboxylic acid groups of MIONs and amine groups of dye. The obtained results indicated that these multifunctional MIONs with rich surface chemistry exhibit admirable potential in biomedical applications.

Improved ferromagnetic behavior and novel near-infrared photoluminescence in Mg/Mn-codoped CuCrO2 ceramics

Cu(Cr0.96−xMg0.04Mnx)O2−δ ceramics (0 ≤ x ≤ 15 at.%) were prepared by solid-state reaction. The influence of Mg acceptor codoping on microstructure, magnetic, and optical properties was studied. The codoping with Mg acceptors and the resulting lattice expansion are both favorable for the enhancement of hole density. Furthermore, the lower valence of Mg2+ compared with Cr3+ enables the mixed valence state of Mn ions: Mn3+ and Mn4+, and hence induces the hole-mediated double-exchange mechanism not only between Mn3+ and Cr3+ but also between Mn3+ and Mn4+. The coexistence of two ferromagnetic interactions and the high hole density are responsible for the improved saturation magnetization and Curie temperature. For photoluminescence, an unusual near-infrared emission at 1.5 eV is observed in the Mn-contained samples and can be attributed to the internal transition between the e and t2 states of the Mn3+ impurity band. The emission intensity is primarily affected by two factors: the Mn3+ concentration and the position of the Fermi level. The results show that codoping with Mg acceptors is an effective way to strengthen the hole-mediated ferromagnetic interactions in CuCrO2 delafossite.