Finite-size scaling law of the Néel temperature in hematite nanostructures

Abstract

Finite-size scaling relation of the Curie temperature in barium hexaferrite plateletsWe report high-temperature magnetic properties of single-crystalline hematite (a-Fe 2 O 3 ) nanostructures with different shapes. Magnetic measurements under a high vacuum (<9.5 Â 10 À6 Torr) up to 920 K were used to characterize thermal stability of the nanostructures. The onset temperature of the a-Fe 2 O 3 to Fe 3 O 4 phase transformation and the transformed fraction were found to depend strongly on the shape of the nanostructure. The data demonstrate that the phase transformation mainly occurs at the (001) surfaces. The high thermal stability of the nanoring and nanotube samples allows us to accurately measure their N eel temperatures. The N eel temperatures of the nanoring and nanotube samples were found to decrease with decreasing the mean wall-thickness of the nanoring/nanotube assembly. The data confirm the two-dimensional finite-size scaling law for the N eel temperature. V C 2014 AIP Publishing LLC. [http://dx.

Mean-field modelling of magnetic nanoparticles: The effect of particle size and shape on the Curie temperature

“…In the smallest particles, T C is found to be 221 of the scaling exponent with respect to particle shape can be seen. This consistency of results close to the accepted value of the scaling exponent contrasts with the range of values of ν found in other studies [9,10,12,15].…”

“…Studies of hematite and magnetite nanoparticles have found values for ν in the range of 0.6-0.8 [9,10], close to the 50 expected value of 0.7043 [11] for the 3D Heisenberg model. 51 A value of ν = 1.06 was determined from work conducted on 52 Ni nanoparticles [12], with line dislocations near the surface 53 of the nanoparticles suggested as the cause of this discrepancy.…”

β-NMR Investigation of the Depth-Dependent Magnetic Properties of an Antiferromagnetic Surface

“…In contrast to the latter strong effect on T M , finite size only weakly affects the second-order Néel transition. Recent high-T data on hematite nanostructures indicates that T N obeys the standard form ðT c =T 0 Þ ¼ 1 − ðL 0 =LÞ 1=ν governed by a typical suppression length L 0 ¼ 2.3 nm, and a scaling exponent near the Ising value ν ¼ 0.6 [38]. Applying the same form to the Morin transition, Fig.…”

α-Fe2O3@C nanorings as anode materials for high performance lithium ion batteries

“…2b). From the outer diameters, thickness, and length histograms [20], the mean outer diameters, thickness, and length are found to be 148, 50, and 115 nm for the nanorings, respectively. The structural details of a-Fe 2 O 3 and a-Fe 2 O 3 @C nanorings are displayed in Fig.…”