Complex Magnetic Nanostructures

Magnetic interactions in systems composed of nanoparticles in a matrix give rise to phenomena that are observable through magnetic and magnetotransport measurements. In this article, we present some basic concepts and review a useful technique for characterizing those systems, which represents a class of magnetization versus temperature measurement, ZFC-FC curves. Based on this tool we comment on some results on granular systems: diluted, interacting, and percolated superparamagnets. We also discuss how those magnetic features affect magnetotransport properties like giant magnetoresistance, tunneling magnetoresistance, and the giant Hall effect.

Nanosized ferrites and magnetic nanocrystals have attracted significant attention owing to their vast applications in various fields, such as magnetic resonance imaging (MRI) contrast agents, magnetic memory, efficient hyperthermia for cancer therapy, and catalysts. Magnetic nanoparticles (MNPs) have been prepared by ferrite nanoparticles, MFe₂O₄ (M = Mn, Co, Ni, Zn, Mg, Fe, for example). Because of their applications in medical diagnosis technology, sensor technology, information storage, cooling technology, and magnetic warming, MNPs have attracted considerable interest in the last few years. The magnetic properties of MNPs strongly depend on the size of the MNPs. Therefore, MNPs with a controlled size are crucial in controlling properties for different applications in the biomedical field. The efficacy of dopant ions in modifying the resultant MNPs’ size and shape could be directly related to variations in the rate of crystal growth and thermodynamic and kinetic considerations. In some situations, particle growth is due to the existence of some other physicochemical phenomenon like passivation of the nanoparticle surface, charging of the nanoparticles, and compartmentalization of nanoparticles in different zones. Various methods involved in the crystal growth of MNPs are also discussed in this chapter.

In this chapter, we present recent advances in interface properties, and synthetic approaches to and applications of bimagnetic core/shell nanoparticles (NPs). First, a brief overview of magnetic core/shell architectures is presented. Then we introduce the principles behind magnetic and structural properties. In this connection, interface phenomena such as the proximity effect, exchange coupling, and exchange bias are summarized. Furthermore, the effects of crystal morphology and phase composition on these exchange interactions are discussed. Chemical methods to synthesize bimagnetic core/shell NPs, including thermal decomposition, seed-mediated growth, coprecipitation, and hydro/solvothermal approaches, are presented. Once produced, surface properties of the core/shell architecture need to be modulated since each application has special requirements. Moreover, a section devoted to the surface functionalization of NPs is given. Finally, applications of bimagnetic core/shell NPs in hyperthermia, magnetic resonance imaging, permanent magnets, and magnetic recording data, among other areas, are discussed in more depth.

Bifunctional nanosized materials, coassembling magnetic and photonic features into single-entity nanostructures with cooperatively enhanced performances, are remarkable because of their potential multimodal biomedical applications, for example, as drug delivery carriers, MRI contrast agents, and magnetic hyperthermia for cancer therapy. Therefore, extensive research work has been conducted over the last decade to study the magnetic and luminescent properties as well as biomedical applications of bifunctional nanostructures based on magnetic nanoparticles and trivalent rare-earth ions. Another area of great research interest is magnetic and photonic nanomaterials containing magnetic nanoparticles functionalized with quantum dots, fluorescent dyes, and luminescent complexes. The aim of this chapter is to present a concise overview of the key concepts of various strategies to fabricate bifunctional nanomaterials, as well as their magnetism and luminescence behaviors. In keeping with the title of the book, the content of the chapter is presented in an efficient way to facilitate understanding by nonspecialized readers. Finally, the manuscript contains a section on multimodal biomedical applications of magnetic and luminescent nanomaterials.

This chapter describes the capabilities of X-ray absorption spectroscopies—X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and X-ray magnetic circular dichroism (XMCD)—for the characterization of magnetic nanoparticle (NP) systems. These techniques constitute very useful methods for directly and selectively examining the electronic state, magnetic properties, and local structure of atoms composing the particles. An overview of these techniques from the theoretical, technical, and experimental point of view is given. Some examples of how the use of these techniques for the characterization of diverse NP systems has offered unparalleled information about their local structure, and their electronic and magnetic properties are presented.

In this chapter, we present the results of studies conducted on the magnetic properties that developed in ultrasmall bare Ag nanoparticles and the critical particle size for developing a sizable spontaneous magnetic moment in the nanoparticles. Seven sets of bare Ag nanoparticle assemblies, with diameters from 2 to 36 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the assemblies. Lattice relaxation from the small size effect is clearly revealed in particles with a diameter smaller than 12 nm, where the electron charges are more extensively distributed toward the central regions of the two nearest neighbors. The extension of the electron charge distribution is not isotopic in all crystallographic directions, revealing that redistribution involves not only spherically distributed 5s electrons but also includes directional 4d electrons. The isothermal magnetization M(H _a) curves of the particle superspins reveal Langevin field profiles. Contributions to the magnetization from particles of different sizes in the assemblies were considered when analyzing the M(H _a) curves. The results show that the maximum superspin moment will appear in 2.6 nm Ag particles. The atoms on the surface and in the core of the bare Ag nanoparticles contribute to the superspin moment. Magnetic field–induced Zeeman magnetization from the quantum confined Kubo gap opening is revealed in Ag nanoparticles smaller than 8 nm in diameter. It is the disruptions of lattice periodicity that trigger the redistribution of electron charges for the development of spontaneous superspin in Ag nanoparticles.

Multifunctional magnetic nanostructures have been appealing in nanoscience owing to their manifold importance in the superfluity of electronic devices and biomedical applications. The integration of multiple discrete functionalities of two or more nanoparticles in a single hybrid system with different types of structures leads to diverse execution capabilities in, for example, catalysis, magnetic sensors, magnetic read heads, and storage devices. These hybrid systems require a theoretical approach to realize their various unknown characteristics. This chapter presents a brief introduction to multifunctional complex magnetic nanostructures, their synthesis and characterization techniques, along with important applications in the magnetic sector. The major focus is on core-shell and dumbbell nanoparticles. Progress in theoretical models to explain complex magnetic phenomena is also discussed.

Recent statistics indicate that more people are dying from unsafe water annually than from all forms of violence combined, including war. Providing access to clean water has now become the first priority around the world. But natural water resources have been contaminated by industrial, agricultural, and harmful human activities, and water demands are increasing daily. One of the approaches being explored in many countries to tackle this challenge of increasing access to clean drinking water is the application of nanotechnology. The unique and novel properties of nanoparticles make them well suited for treating water. Nanotechnology offers an opportunity to refine and optimize current techniques and to provide new and novel methods of purifying water. Among them, magnetic nanomaterials have received much attention due to their great biocompatibility, excellent adsorption, and fast separation properties. In this chapter we aim to present all aspects and roles of magnetic nanoparticles (MNPs) in water purification as well as treatment. The chapter covers both the pros and cons of MNPs in water treatment and concludes with recent investigations of the issue of nanotoxicity and its implications for the future.

Since its first isolation in 2004, graphene, a two-dimensional single layer of sp²-hybridized carbon sheet with hexagonal packed lattice structure, has been in the spotlight around the world. The unique and exceptional physicochemical properties, such as high thermal stability, high surface area, excellent recyclability, and, most importantly, on-demand surface engineering with a range of nanoscale structures, of graphene and its subtypes have triggered colossal scientific interest with the aim of transforming the global market for the construction of state-of-the-art composite materials. Among such materials, magnetic graphene nanocomposites, nanomaterials composed of inorganic magnetic constituents in the form of either particles or any varying shape embedded in graphene as hosting matrix, are of particular interest, and the scope of their usefulness has progressively matured in the past few years for contemporary yet wide technological applications, including, but not limited to, heterogeneous catalysis, enzyme mimics and biosensing, and molecular imaging.

Only a few innovative technologies and discoveries have the potential to transform our physical world. The discovery of two-dimensional materials is one such discovery. In 2004, a new class of atomically thin materials, graphene, which has excellent surface features and possesses extraordinary properties, was discovered after isolation from graphite. Graphene, together with some magnetic nanoparticles, has given rise to graphene-based multifunctional magnetic nanocomposites, which have great potential in a variety of applications starting with data storage and security/sensors to biomedical applications. The potential use of graphene-based multifunctional magnetic nanocomposites in biological beings has led to remarkable developments in research and theragnosis of various diseases. Graphene-based multifunctional magnetic nanocomposites, accomplished of drug delivery and theragnosis, are likely to play a momentous role in the emergence of tailored medical treatment. To that end, this chapter offers a comprehensive state-of-the-art overview of progress made in graphene-based multifunctional magnetic nanocomposites and their applications in various biomedical fields. The biocompatibility requirements and functionalization approach of these nanocomposites are also reviewed.

Hyperthermic treatment of cancer by magnetic nanoparticles has shown promising results in recent years. Magnetic nanoparticles in the form of stable fluids can be transported to the effected cells noninvasively through a variety of drug delivery routes. Upon stimulation by a radio frequency magnetic field, these nanoparticles induce local heat remotely, which causes the temperature in organs and tissues containing tumoral cells to rise and causes the death of infected cells. The heat generation mainly results from three independent physical mechanisms, Néel relaxation, Brownian relaxation, and hysteresis loss. The involvement of each mechanism firmly depends on the crystal size, crystal structure, morphology, and degree of aggregation of the nanoparticles. Nanostructures based on iron oxide and its relevant ferrites, such as cobalt ferrite and nickel ferrite, in a range of a few nanometers, showing superparamagnetic properties have been investigated extensively for magnetic hyperthermia. This chapter will cover different aspects of magnetic hyperthermia from a material science point of view, including mechanisms, materials, crystal size, shape, the effect of architecture on heat generation efficiency, and practical procedures to measure the therapeutic properties of fluidic nanoparticles preinjection.

During the last couple of decades extensive investigation efforts have been directed toward the exploitation of iron oxide nanoparticles in biomedical and bioengineering applications. To improve these applications, high saturation magnetization values and sizes smaller than 100 nm with overall narrow particle size distribution are required, so that the particles have uniform physical and chemical properties. In addition, these applications need special surface coating of the magnetic nanoparticles, which must be not only nontoxic and biocompatible but also allow a targetable delivery with particle localization in a specific area. This chapter covers the most recent challenges and advances for numerous biomedical applications such as magnetic resonance imaging contrast enhancement, tissue repair, immunoassay, detoxification of biological fluids, hyperthermia, drug delivery, gene delivery, bioseparation, cell tracking, cell separation, and manipulation of cellular organalles.