Evaluation of Hematite Nanoparticles Weak Ferromagnetism
- PDF / 1,144,973 Bytes
- 8 Pages / 595.276 x 790.866 pts Page_size
- 31 Downloads / 161 Views
ORIGINAL PAPER
Evaluation of Hematite Nanoparticles Weak Ferromagnetism Sadeq H. Lafta 1 Received: 4 June 2020 / Accepted: 22 July 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Nanoparticles of hematite were prepared by the precipitation method. Structural, hysteresis, moment-temperature, ferromagnetic resonance tests were performed. All hematite peaks were appeared in the XRD pattern with corundum phase of crystallite size of 15 nm. The SEM images showed that the average particle size is around 21 nm with ribbed shape. Different Fe–O bond peaks were registered in the FTIR test. The sample showed weak ferromagnetic state as was checked by M-H and M-T tests. The M-H test showed opened loop at low-field region and linear behavior at high-field region with susceptibilities of 1.4 × 10−5 emu/g Oe and 7.5 × 10−6 emu/g Oe respectively. Fitting by Langevin equation is conducted to find the particle moment. Morin temperature was found to be 17.77 K, while Neel temperature was about 614 K. A comparison with literature was given. FMR test showed a shift in the resonance field with broadened line having Landé g factor of 1.90498 at 9.3 GHz. Keywords Hematite . Weak ferromagnetism . Moment . FMR . Morin temperature
1 Introduction Hematite is the more familiar iron oxide with the chemical formula Fe2O3. It has a crystalline structure of a rhombohedral that related to the hexagonal family. The iron atoms are surrounded by six oxygen atoms forming non-regular octahedron [1, 2], involving two sublattices. Magnetically, hematite can be antiferromagnetic material with canted spins [3, 4], when the two lattices have equally antiparallel spins or classified as a strong paramagnetic depending on particle size and temperature [5, 6]. Pure hematite has two magnetic phase transition temperatures causing magnetic moment reorientation for the bulk material with no change in crystalline phase. They are known as Morin temperature TM around 260 K and Neel temperature TN around 950 K. Below the first one, hematite is antiferromagnetic where no canting is found, and the Fe3+ moments are opposite to each other along the c-axis of crystalline direction [111]. Above TM and below TN, hematite has a canted uncompensated spin by an angle of 5°, so there are no completely opposite spins. This produces a small net magnetization of 1 emu/cc due to super interaction between spins, with * Sadeq H. Lafta [email protected]; [email protected] 1
Applied Science Department, University of Technology, Baghdad, Iraq
orientation normal to c-axis in the basal plane producing weak ferromagnetic state. The lowering of particle size and increasing surface effects (as dominate spins) reduce the TM until it vanishes. The remaining phase is the canted antiferromagnetic one. When particle size is < 20 nm, this produces a fastrelaxing state or what is called superparamagnetic state, which is affected by exchange interaction among particles [4]. Above TN, hematite particles behave as paramagnetic material. Other factors t
Data Loading...
