Size Distribution and Frustrated Antiferromagnetic Coupling Effects on the Magnetic Behavior of Ultrafine Akaganéite (β-FeOOH) Nanoparticles

Abstract

The magnetic properties of low dimensional materials of several iron oxyhydroxyde phases, such as akaganéite (β-FeOOH) or lepidocrocite (γ-FeO(OH)), remain poorly explored; probably due to their specific preparation as single crystalline phase requires special conditions owing to their structural instability. In the present work, ultra-fine akaganéite nanoparticles were prepared by the hydrolysis of FeCl 3 solutions at room temperature induced by the presence of NaOH. The resulting product was characterized by several analytical techniques. Structural investigations using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) revealed that the sample was mainly constituted by rather-equiaxial akaganéite nanocrystals with mean diameter of 3.3 ± 0.5 nm. In addition, a small amount of rod-like akaganéite particles with 23 ± 5 nm in length and 5 ± 1 nm in width was also detected. The study of the respective dependences of the dc magnetization and the ac susceptibility on temperature and exciting magnetic field revealed complex magnetic relaxation processes, high coercivity values at low temperature and exchange bias effect. These results have been tentatively explained considering size distribution effects and the presence of superparamagnetic and spin glass-like contributions arising from the frustration of the antiferromagnetic order owing to surface effects and an insufficient filling of the akaganéite channels with Clanions.

Silica-Coated and Bare Akaganeite Nanorods: Structural and Magnetic Properties

“…Luna et al reported magnetic properties of akaganeite nanocrystals with mean diameter of (3.3 ± 0.5) nm and with a small amount of rodlike akaganeite particles with (23 ± 5) nm in length and (5 ± 1) nm in diameter. 20 These studies revealed complex magnetic relaxation processes, high values of coercivity and an exchange bias effect, both at low temperatures. The conclusion was that these results arise from the frustration of the antiferromagnetic order owing to surface effects and an insufficient filling of akaganeite channels with Cl -anions.…”

“…a spin imbalance due to a lack of particles' structural perfection. [19][20][21] Among antiferromagnetic iron oxides and hydroxides, akaganeite is less well known, possibly due to the inherent difficulties in preparation of a single crystalline phase: such a preparation requires special conditions owing to the akaganeite's structural instability. 20 Akaganeite is interesting due to its structural, magnetic and catalytic properties, as well as for practical applications such as for the removal of pollutants, sorption, ion-exchange, lithium-air batteries.…”

“…[22][23][24][25][26][27] Moreover, the β-FeOOH phase is important and widely used as a precursor in the 4 preparation of iron, hematite, maghemite and magnetite nanosized materials. 16,[28][29][30][31][32] Akaganeite is an antiferromagnetic material with a Néel temperature in the range of T N ≈ 240-299 K. 12,20,33 A substantial reduction of the Néel temperature, down to T N = 15 K, has been observed in amorphous β-FeOOH nanowires. 19 It has also been observed that the Curie-Weiss temperature varies within a wide range for differently synthesized β-FeOOH materials.…”

“…12,33 It has been reported in the literature that the wide ranges of the two temperatures, T N and θ, are influenced by interstitial water molecules, vacancies and chlorine anions. 12,20,33 Moreover, the size of particles and their morphology have a large influence on the magnetic properties of β-FeOOH. In particular, some researchers have focused on the ferromagnetism of the antiferromagnetic β-FeOOH nanoparticle systems below the Neel temperature and its superparamagnetism at room temperature.…”

Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

“…Therefore, shape-controlled synthesis of one-dimensional -FeOOH nanomaterials, in particular rods, fibers and wires, has attracted the increasing attention in recent years [1,3,11]. -FeOOH nanoparticles were traditionally prepared through hydrolysis of FeCl 3 in acidic or basic media.…”