Introduction to magnetic materials

Nano-structural effects on Hematite (α-Fe2O3) nanoparticle radiofrequency heating

“…The rugby ball and nanodiamond shaped nanoparticles did not reach magnetic saturation at the maximum magnetic field of 50 kOe. The rugby ball shaped hematite particles (~178 nm) display magnetic behavior similar to that of bulk hematite (~3 µm; weakly ferromagnetic [10][11][12]) at room temperature [11,26]. The other hematite nanoparticle shapes (nanospheres, nanodiamonds, nanosheets, and nanorods) show superparamagnetic-like behavior, based on their very low coercivity (H c ) and magnetic remanence (M r ) values [27].…”

“…From these images, polycrystalline materials were defined as particles having multiple grain boundaries that separated sections of difference crystal growth directions or crystallites. The grain boundaries serve as magnetic domains, which contributes to hysteretic heating of the material when subjected to an AMF [10]. Particles that did not present grain boundaries (i.e., having a crystallite size approximately equal to the average particle size determined by SEM) were concluded to be single crystalline particles.…”

“…As the most stable iron oxide under acidic [1] and ambient conditions [2], hematite (i.e., α-Fe 2 O 3 ) has been heavily studied for a variety of applications including: waste water treatment [2][3][4][5], catalysis [6], gas sensors [2], and electrodes [7]. Although environmentally benign and biocompatible [8,9], bulk hematite is not suitable for radio frequency (RF) magnetic heating applications because it is weakly ferromagnetic at room temperature [10,11] (i.e., M S,bulk ~ 0.3 emu/g [12]).…”

Intriguing role of TiO2 in glass‐ceramics: Bioactive and magneto‐structural properties

“…Superparamagnetism is attained when the size of particle is reduced to a threshold limit, below which it behaves as single domain system. 32 Iron ions, in amorphous matrices, assemble together to form nanometric clusters. 33,34 Also, as glasses are highly disordered materials, the magnetic ordering takes place only up to very short distances.…”

“…However, even in single domain region, the size of particles needs to be below a critical limit to exhibit superparamagnetism. 32 Apparent coercivity of T1 and T4 glasses indicates the presence of magnetic clusters having size greater than the threshold size limit for superparamagnetism. The magnetization (M) of superparamagnetic materials is explained in terms of Langevin function as follows 35 :…”