Faculty RWTH Aachen University Aachen, Germany
Codruta Soica
Faculty of Pharmacy Department of Toxicology “Victor Babes” University of Medicine and Pharmacy Timisoara, Romania
Gabriela Fabiola Ştiufiuc
Faculty of Physics “Babes‐Bolyai” University Cluj‐Napoca, Romania
Rareș Ionuț Ştiufiuc
Department of Pharmaceutical Physics and Biophysics “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj‐Napoca, Romania;
Med Future Research Center for Advanced Medicine “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj‐Napoca, Romania
Romulus Tetean
Faculty of Physics “Babes‐Bolyai” University Cluj‐Napoca, Romania
Boyan Todorov
Faculty of Chemistry and Pharmacy Sofia University “St. Kliment Ohridski” Sofia, Bulgaria
Valentin Toma
Med Future Research Center for Advanced Medicine “Iuliu Hațieganu” University of Medicine and Pharmacy Cluj‐Napoca, Romania
Francois Vernay
Laboratoire PROMES CNRS UPR 8521 Université de Perpignan Via Domitia Rambla de la Thermodynamique Tecnosud, Perpignan, France
1 An Introduction to Magnetic Nanoparticles: From Bulk to Nanoscale Magnetism and Their Applicative Potential in Human Health and Medicine
Costica Caizer1, Shital Bonde2, and Mahendra Rai2
1 Physics Faculty, Department of Physics, West University of Timisoara, Timisoara, Romania
2 UGC – Basic Science Research Faculty, Department of Biotechnology, SGB Amravati University, Amravati, Maharashtra, India
1.1 Magnetism of Nanoparticles: From Bulk to Nanoscale
1.1.1 Introduction
The bulk magnetic material has specific magnetic properties depending on the type of magnetic material and the form of magnetic ordering (Smit and Wijin 1961; Kneller 1962; Jacobs and Bean 1963; Vonsovskii 1974; Kojima 1982; Rosensweig 1985; Cullity and Graham 2009). Magnetic materials can be diamagnetic, paramagnetic, and with ordered forms of magnetism. The magnetic ordered materials can be ferromagnetic, antiferomagnetic, ferimagnetic, and some more complex magnetic structures. Diamagnetic materials show a very weak magnetization (M) induced by the application of the external magnetic field (H) (Figure 1.1a‐(I)), in the opposite direction to the magnetic field (Figure 1.1b‐(I)), due to the phenomenon of electromagnetic induction (Faraday) that modifies the orbital and spin motion of atomic electrons. In the absence of the magnetic field, this material has no atomic (or molecular) magnetic moment. The paramagnetic materials show a weak magnetization in an external magnetic field (Figure 1.1a‐(II)), but in the same direction of the applied magnetic field (Figure 1.1b‐(II)), as a result of the reorientation of the permanent atomic magnetic moments in the magnetic field. This material has, at molecular level, permanent magnetic moments (in the absence of the external magnetic field), which does not interact magnetically with each other. In the case of ferromagnetic materials, an intense magnetization is obtained in the presence of the external magnetic field (Figure 1.1a‐(III)), in the same direction with the applied magnetic field (Figure 1.1b‐(III)), due to the existence of ordered (aligned) atomic (or molecular) magnetic moments under the action of exchange forces (exchange interaction) existing at the molecular level of a quantum nature.
Figure 1.1 (a) Schematic field dependencies of magnetization of (I) diamagnetic, (II) paramagnetic, and (III) ferromagnetic materials.
Source: Yamauchi (2008). Reproduced with permission from John Wiley & Sons.
(b) Schematic representation of the magnetization of different magnetic materials in the external magnetic field: (I) diamagnetic, (II) paramagnetic, (III) ferromagnetic.
Source: Caizer (2013). Eurobit Publishing.
In the ferromagnetic crystal, the atoms with spin magnetic moment (the orbital magnetic moment being frozen by the presence of the crystalline electric field) are located at small distances between them, thus, generating the exchange interaction that aligns the spin magnetic moments over large spatial atomic distances, which can reach up to tens of microns (μm) (magnetic domains) (Caizer 2004a). In the antiferromagnetic crystal, the equal atomic magnetic moments are aligned to 180°, thus existing as a compensation for these, so that in the absence of the external magnetic field, the magnetization is nonexistent while in the presence of a magnetic field that is very low. On the other hand, in the case of ferrimagnetics, where, in the absence of the external magnetic field, there is a noncompensation of the magnetic moments aligned to 180 as a result of the exchange interaction (more precisely a superexchange), and there will be a significantly higher magnetization in the presence of the external magnetic field, but of a lower value compared to ferromagnetics.
A classification of the diamagnetic, paramagnetic, and ferromagnetic materials, depending on the amplitude of the magnetic susceptibility (χ) (the intrinsic parameter of magnetic materials) is given below (Caizer 2013), and Table 1.1 shows the specific value ranges to magnetic susceptibility for different types of magnetic materials/substances (LIO – linear, isotropic, and homogeneous), without there being a strict delimitation between them.
Table 1.1 Magnetic susceptibility values for different bulk magnetic materials.
| Type of magnetic material | Diamagnetic | Paramagnetic | Ferromagnetic |
|---|---|---|---|
| χ | −(10−4 – 10−6) (χ < 0) | 10−3 – 10−5 (χ > 0) | 102 – 105 (χ ≫ 0) |
When the size of the magnetic material, ferro‐ or ferrimagnetic, is reduced to the range of nm – tens of nm, it was found
