Annealing control of hydrothermally grown hematite nanorods: Implication of structural changes and Cl concentration on weak ferromagnetism

Author(s)

Carvalho-Jr, W. M. ; Mendonca-Ferreira, L. ^[1] ; Costa, F. N. ^[1] ; Ferreira, F. F. ^[1] ; Muche, D. N. F. ^{[2, 3]} ; Tofanello, R. A. ^[1] ; Castro, R. H. R. ^{[2, 3]} ; Souza, F. L. ^{[2, 3, 1]}

Affiliation

^[1] Carvalho-Jr, Jr., W. M., Univ Fed Abc, CCNH, BR-09210170 Santo Andre, SP - Brazil

^[2] Univ Calif Davis, Dept Mat Sci & Engn, One Shields Ave, Davis, CA 95616 - USA

^[3] Univ Calif Davis, NEAT ORU, One Shields Ave, Davis, CA 95616 - USA

• Document type: Journal article
• Source: Journal of Alloys and Compounds; v. 799, p. 83-88, AUG 30 2019.
• Web of Science Citations: 0

Abstract

In-situ X-ray diffraction coupled with thermogravimetry and differential scanning calorimetry were used to elucidate the crystal phase transition from akaganeite to hematite nanorods. The results indicate that though complete phase transformation occurs at similar to 663 K, residual chlorines from the hydrothermal synthesis conditions strongly affect spin moment. The high temperature (>1023 K) shock-annealing reduced the chlorine concentration and consequent suppress most of surface defects on the rods. High temperature annealed hematite nanorods were then studied in terms of magnetic properties under different applied hydrostatic pressures and exhibited a shift of T-M to higher values, from 261 to 282 K with initial rate (partial derivative T-M/partial derivative P coefficient) of 46 K GPa(-1). Such positive dependence of T-M with hydrostatic applied pressure is consistent with several works reported in the literature investigating different morphologies in bulk and at nanoscale. In fact, gradual reduction of Cl species increases the spin mobility allowing the appearance of weak-ferromagnetism at room temperature. The crossover results strongly support the hypothesis that Cl dominates spin mobility. (C) 2019 Elsevier B.V. All rights reserved. (AU)

• FAPESP's process: 16/02157-2 - Understanding the hematite nanostructured surface performing water adsorption microcalorimetry
• Grantee: Flavio Leandro de Souza
• Support Opportunities: Scholarships abroad - Research
• FAPESP's process: 13/05471-1 - Effect of dopants in semiconductor nanostructures and their impact on photocatalytic performance
• Grantee: Waldemir Moura de Carvalho Junior
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 13/07296-2 - CDMF - Center for the Development of Functional Materials
• Grantee: Elson Longo da Silva
• Support Opportunities: Research Grants - Research, Innovation and Dissemination Centers - RIDC
• FAPESP's process: 11/19924-2 - Study and development of advanced novel materials: electronic, magnetic and nanostructured: an interdisciplinary approach
• Grantee: Carlos Rettori
• Support Opportunities: Research Projects - Thematic Grants