In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

The aim of this article is to provide a comprehensive review of current research activities that center on superparamagnetic colloids. We begin with an overview of synthetic strategies that have been developed for generating both nanoscale and mesoscale superparamagnetic colloids, with a focus on those systems that can be prepared as monodisperse samples and in relatively large quantities. We then discuss a variety of techniques that have been exploited for modifying surface properties, as well as for controlling the assembly and patterning of these magnetically active colloids. Towards the end, we highlight a range of innovative applications enabled by the unique combination of superparamagnetism and colloidal suspension. We conclude this review article with personal remarks and perspectives on the directions toward which future research in this area might be directed.

Superparamagnetic Colloids: Controlled Synthesis and Niche Applications**

This paper introduces a special issue on the ecotoxicology and environmental chemistry of nanoparticles (NPs), and nanomaterials (NMs), in the journal Ecotoxicology. There are many types of NMs and the scientific community is making observations on NP ecotoxicity to inform the wider debate about the risks and benefits of these materials. Natural NPs have existed in the environment since the beginning of Earth’s history, and natural sources can be found in volcanic dust, most natural waters, soils and sediments. Natural NPs are generated by a wide variety of geological and biological processes, and while there is evidence that some natural NPs can be toxic, organisms have also evolved in an environment containing natural NPs. There are concerns that natural nano-scale process could be influenced by the presence of pollution. Manufactured NPs show some complex colloid and aggregation chemistry, which is likely to be affected by particle shape, size, surface area and surface charge, as well as the adsorption properties of the material. Abiotic factors such as pH, ionic strength, water hardness and the presence of organic matter will alter aggregation chemistry; and are expected to influence toxicity. The physico-chemistry is essential to understanding of the fate and behaviour of NPs in the environment, as well as uptake and distribution within organisms, and the interactions of NPs with other pollutants. Data on biological effects show that NPs can be toxic to bacteria, algae, invertebrates and fish species, as well as mammals. However, much of the ecotoxicological data is limited to species used in regulatory testing and freshwater organism. Data on bacteria, terrestrial species, marine species and higher plants is particularly lacking. Detailed investigations of absorption, distribution, metabolism and excretion (ADME) remain to be performed on species from the major phyla, although there are some data on fish. The environmental risk assessment of NMs could be performed using the existing tiered approach and regulatory framework, but with modifications to methodology including chemical characterisation of the materials being used. There are many challenges ahead, and controversies (e.g., reference substances for ecotoxicology), but knowledge transfer from mammalian toxicology, colloid chemistry, as well as material and geological sciences, will enable ecotoxicology studies to move forward in this new multi-disciplinary field.

http://users.uoa.gr/~econom/thalis/Coordinator/Papers/VALSAMI-JONES-%20The%20ecotoxicology%20of%20nanoparticles%20and%20nanomaterials,%202008l.pdf

The ecotoxicology of nanoparticles and nanomaterials: current status, knowledge gaps, challenges, and future needs

https://research.birmingham.ac.uk/portal/files/33294910/Larson_et_al_State_Vaccine_Confidence_EBioMedicine.pdf

The State of Vaccine Confidence 2016: Global Insights Through a 67-Country Survey

Vaccination is one of the great achievements of the 20th century, yet persistent public-health problems include inadequate, delayed, and unstable vaccination uptake. Psychology offers three general propositions for understanding and intervening to increase uptake where vaccines are available and affordable. The first proposition is that thoughts and feelings can motivate getting vaccinated. Hundreds of studies have shown that risk beliefs and anticipated regret about infectious disease correlate reliably with getting vaccinated; low confidence in vaccine effectiveness and concern about safety correlate reliably with not getting vaccinated. We were surprised to find that few randomized trials have successfully changed what people think and feel about vaccines, and those few that succeeded were minimally effective in increasing uptake. The second proposition is that social processes can motivate getting vaccinated. Substantial research has shown that social norms are associated with vaccination, but few int...

https://journals.sagepub.com/doi/pdf/10.1177/1529100618760521

Increasing Vaccination: Putting Psychological Science Into Action:

10% Co‐doped BiFeO3 nanoparticles have been prepared by a low temperature sol‐gel method. XRD result shows that particles are single phase in nature and crystallizes in distorted perovskite structure (space group R3c) with average particle size of 60 nm. Room temperature ferromagnetism along with saturation magnetization of about 2.24 emu/g and high coercive field of 1260 Oe has been found by VSM measurements. Mossbauer data can be fitted with single magnetic sextet of isomer shift about 0.35 mm/s and hyperfine field about 49 T indicating Fe3+ nature of Fe atom present in Co‐doped BiFeO3 nanoparticles.

Preparation and Magnetic Studies on 10% Co‐doped BiFeO3 Multiferroic Nanoparticles

Introduction Following the withdrawal of Sabin type 2 from trivalent oral poliovirus vaccine (tOPV) in 2016, the introduction of ≥1 dose of inactivated poliovirus vaccine (IPV) in routine immunization was recommended, either as 1 full dose (0.5mL, intramuscular) or 2 fractional doses of IPV (fIPV-0.1mL, intradermal). India opted for fIPV. We conducted a comparative assessment of IPV and fIPV. Methods This was a 4-arm, open-label, multicenter, randomized controlled trial. Infants were enrolled and vaccines administered according to the study design, and the blood was drawn at age 6, 14, and 18 weeks for neutralization testing against all 3 poliovirus types. Results Study enrolled 799 infants. The seroconversion against type 2 poliovirus with 2 fIPV doses was 85.8% (95% confidence interval [CI]: 80.1%-90.0%) when administered at age 6 and 14 weeks, 77.0% (95% CI: 70.5-82.5) when given at age 10 and 14 weeks, compared to 67.9% (95% CI: 60.4-74.6) following 1 full-dose IPV at age 14 weeks. Conclusion The study demonstrated the superiority of 2 fIPV doses over 1 full-dose IPV in India. Doses of fIPV given at 6 and 14 weeks were more immunogenic than those given at 10 and 14 weeks. Clinical Trial Registry of India (CTRI). Clinical trial registration number was CTRI/2017/02/007793.

Immunogenicity of Fractional Dose Inactivated Poliovirus Vaccine in India.

In order to fabricate a nanostructure precisely, the effect of different parameters involved in the fabrication processes should be extensively studied. We have studied the effect of beam parameters such as beam dwell time, mode of deposition as well as pattern size, on focused-ion-beam-induced deposition of nanopillars. While fabricating the nanopillars in the circular and serpentine mode deposition, long tails of the deposited material are observed. The amount deposited in the tails is found to be a function of the beam dwell time as well as the diameter of the pillar. The tail disappears at higher beam dual time and pillar diameter. The elemental composition of the tail is found to be same as that of the pillar.

Beam scanning effect on focused-ion-beam-induced processing

Electric field gradient (efg) is calculated at the centre of the cell in the simple tetragonal crystal The method uses Euler-Maclaurin summation formula and makes the planewise summation in the direct crystal space without any special regrouping of charges in point charge model The results are in fair agreement with previous results of de Wette on the same system using Fourier transform to reciprocal space

Electric field gradients in simple tetragonal lattice at interstitial site

Undoped and calcium substituted hematite (α-Fe₂O₃) nanoparticles are synthesized by surfactant-directed co-precipitation and post annealing method. The annealed nanoparticles were found to be in single phase in nature and crystallize in the rhombohedral structure with space group R3c as confirmed by Rietveld refinement of the X-ray diffraction (XRD) data. Average crystallite sizes are calculated to be 20 to 30 nm and 50 to 60 nm for the nanoparticles annealed at 400 and 600 °C respectively. Mossbauer spectra for all the nanoparticles could be fitted with a sextet corresponding to the single magnetic state of the iron atoms in its Fe³⁺ state in the hematite matrix. The FTIR and Raman spectra of all the samples correspond to specific modes of α-Fe₂O₃. UV-Vis spectra of annealed samples showed broad peaks in the range of 525-630 nm resulting from spin-forbidden ligand field transition together with the spin-flip transition among the 2t₂g states. The estimated band gap energies were in the range of 1.6 to 1.9 eV which are much lower than the reported values for nano hematite. From the room temperature magnetic hysteresis loop measurements, weak ferromagnetic behavior is observed in all undoped and Ca²⁺ doped hematite samples. Morin temperature (T(M)) is calculated to be 257 and 237 K for 1.45% doped samples with particle size 54 and 27 nm respectively. The sample with Ca content of 1.45 wt% when annealed at 400 °C showed that the particles were of different shapes which included both quasi spherical and rod shaped. On annealing the same sample at 600 °C, the nanorods collapsed to form bigger spherical and ellipsoidal particles.

Harish Verma

Papers

Preparation and Magnetic Studies on 10% Co‐doped BiFeO3 Multiferroic Nanoparticles

Immunogenicity of Fractional Dose Inactivated Poliovirus Vaccine in India.

Beam scanning effect on focused-ion-beam-induced processing

Electric field gradients in simple tetragonal lattice at interstitial site

Structural and Magnetic Properties of Dilute Ca²⁺ Doped Iron Oxide Nanoparticles