Victor Guimarães - Academia.edu (original) (raw)

Papers by Victor Guimarães

Nanocomposites - New Trends and Developments, 2012

that have been used in diverse devices and systems for industrial products. Some traditional appl... more that have been used in diverse devices and systems for industrial products. Some traditional applications of these materials are in cores for motors, generators and transformers, microwave devices, magnetic media used in computers, recording devices, and magnetic cards, among others [3]. There are various metallic elements (Fe, Ni, etc) that have magnetic properties due to their crystalline atomic structure whose spins align spontaneously. Some alloys formed by metallic elements and others including the earth rare elements also have excellent magnetic properties (alnico, samarium-cobalt and neodymium-iron-boron magnets). Finally, the ferrites are a known class of magnetic materials formed by metallic oxides. With the advancement of the material sciences and the emergence of the nanoscience and nanothecnology, new kinds of magnetic materials have been developed and studied in the last years, such as the magnetic nanoparticles, ferrofluids and magnetic nanocomposites. With these materials, new applications could be tested in areas such like electronic, catalysis and biomedicine, among others [4]. 1.1. Ferrites Ferrites are chemical compounds obtained as powder or ceramic body with ferrimagnetic properties formed by iron oxides as their main component, Fe 2 O 3 and FeO, which can be partly changed by others transition metals oxide. The ferrites can be classified according their crystalline structure: hexagonal (MeFe 12 O 19), garnet (Me 3 Fe 5 O 12) and spinel (MeFe 2 O 4), where Me represents one or more bivalent transition metals (Mn, Fe, Co, Ni, Cu, and Zn). The ferrites are classified as "soft" or "hard" magnets, according to their magnetic properties, which refers to their low or high magnetic coercivity, respectively. Hard magnets are not easily demagnetized (curve a), due to their high coercivity and soft magnets are easily magnetized and demagnetized (curve b) with application of a magnetic field, due to their low coercivity. The characteristic magnetic hysteresis curves of these type of magnets are shown in Figure 1 [3,5,6]. The intermediate magnets, generally used in magnetic media, must have coercivity sufficiently high for withholding the information, but sufficiently low to allow for the information to be deleted (curve c) [5,6]. These magnetic ceramics [6] are important in the production of electronic components, since they reduce energy losses caused by induced currents and they act as electric insulators. They can be used in simple function devices such as small permanent magnets, until as sophisticated devices for the electro-electronic industry. Recently, these materials have been discovered as good catalysts [7,8,9] and biomaterials [10,11].

Nanocomposites - New Trends and Developments, 2012

that have been used in diverse devices and systems for industrial products. Some traditional appl... more that have been used in diverse devices and systems for industrial products. Some traditional applications of these materials are in cores for motors, generators and transformers, microwave devices, magnetic media used in computers, recording devices, and magnetic cards, among others [3]. There are various metallic elements (Fe, Ni, etc) that have magnetic properties due to their crystalline atomic structure whose spins align spontaneously. Some alloys formed by metallic elements and others including the earth rare elements also have excellent magnetic properties (alnico, samarium-cobalt and neodymium-iron-boron magnets). Finally, the ferrites are a known class of magnetic materials formed by metallic oxides. With the advancement of the material sciences and the emergence of the nanoscience and nanothecnology, new kinds of magnetic materials have been developed and studied in the last years, such as the magnetic nanoparticles, ferrofluids and magnetic nanocomposites. With these materials, new applications could be tested in areas such like electronic, catalysis and biomedicine, among others [4]. 1.1. Ferrites Ferrites are chemical compounds obtained as powder or ceramic body with ferrimagnetic properties formed by iron oxides as their main component, Fe 2 O 3 and FeO, which can be partly changed by others transition metals oxide. The ferrites can be classified according their crystalline structure: hexagonal (MeFe 12 O 19), garnet (Me 3 Fe 5 O 12) and spinel (MeFe 2 O 4), where Me represents one or more bivalent transition metals (Mn, Fe, Co, Ni, Cu, and Zn). The ferrites are classified as "soft" or "hard" magnets, according to their magnetic properties, which refers to their low or high magnetic coercivity, respectively. Hard magnets are not easily demagnetized (curve a), due to their high coercivity and soft magnets are easily magnetized and demagnetized (curve b) with application of a magnetic field, due to their low coercivity. The characteristic magnetic hysteresis curves of these type of magnets are shown in Figure 1 [3,5,6]. The intermediate magnets, generally used in magnetic media, must have coercivity sufficiently high for withholding the information, but sufficiently low to allow for the information to be deleted (curve c) [5,6]. These magnetic ceramics [6] are important in the production of electronic components, since they reduce energy losses caused by induced currents and they act as electric insulators. They can be used in simple function devices such as small permanent magnets, until as sophisticated devices for the electro-electronic industry. Recently, these materials have been discovered as good catalysts [7,8,9] and biomaterials [10,11].