Core/Shell Nanoparticles: Classes, Properties, Synthesis Mechanisms, Characterization, and Applications

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

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

https://www.andrew.cmu.edu/user/dl0p/laughlin/pdf/PMS.pdf

Amorphous and nanocrystalline materials for applications as soft magnets

Field and frequency dependence of the magneto-impedance in Co-rich amorphous ribbon

100 MeV Si+7 irradiation induced modifications in the structural and magnetic properties of Mg0.95Mn0.05Fe2O4 nanoparticles have been studied by using X-ray diffraction, Mossbauer spectroscopy and a SQUID magnetometer. The X-ray diffraction patterns indicate the presence of single-phase cubic spinel structure of the samples. The particle size was estimated from the broadened (311) X-ray diffraction peak using the well-known Scherrer equation. The milling process reduced the average particle size to the nanometer range. After irradiation a slight increase in the particle size was observed. With the room temperature Mossbauer spectroscopy, superparamagnetic relaxation effects were observed in the pristine as well as in the irradiated samples. No appreciable changes were observed in the room temperature Mossbauer spectra after ion irradiation. Mossbauer spectroscopy performed on a 12 h milled pristine sample (6 nm) confirmed the transition to a magnetically ordered state for temperatures less than 140 K. All the samples showed well-defined magnetic ordering at 5 K, whereas, at room temperature they were in a superparamagnetic state. From the magnetization studies performed on the irradiated samples, it was concluded that the saturation magnetization was enhanced. This was explained on the basis of SHI irradiation induced modifications in surface states of the nanoparticles.

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

Field dependence of second-harmonic amplitude of magnetoimpedance in FeCoSiB joule heated wires

Fourier analysis of the nonlinear response of the impedance signal of amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers is presented. The harmonic components of the voltage signal present a strong asymmetry. A strong variation (around 1400%) of the second-harmonic signal (V2 f) as a function of the applied magnetic field is observed. Nonlinear effects and the asymmetric behavior in harmonics can be associated with the anisotropies induced during the fabrication process. These results can lead to improvement of the performance of future magnetoimpedance sensors.

Large nonlinear magnetoimpedance in amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers

In this study we report microwave experiments on the amorphous ribbon Fe4.6Co70.4Si15B10 using the usual setup for magnetic resonance experiments at 9.4 GHz to observe the cavity response. Several samples cut from the same tape were annealed, either in the presence or in the absence of a magnetic field. For each sample the magnetization and magnetoimpedance (MI) curves were obtained, with MI ratios between 1% and 40%. The magnetic resonance spectrum consists of the usual ferromagnetic line and an anomalous low field cavity response for H<100 Oe. The shape of this low field signal depends on the thermal treatment and on the orientation of the external field. We believe that this signal is in part a ferromagnetic peak but it also carries information of the skin‐depth changes with a sweeping magnetic field.

Marcelo Knobel

Papers

Field and frequency dependence of the magneto-impedance in Co-rich amorphous ribbon

Magnetic Study of Nanocrystalline Ferrites and the Effect of Swift Heavy Ion Irradiation

Field dependence of second-harmonic amplitude of magnetoimpedance in FeCoSiB joule heated wires

Large nonlinear magnetoimpedance in amorphous Co80.89Fe4.38Si8.69B1.52Nb4.52 fibers

Resonant microwave cavity response of amorphous ribbons