Enhanced room temperature ferromagnetism in antiferromagnetic NiO nanoparticles

Journal Article · Sat Aug 15 00:00:00 EDT 2015 · AIP Advances

DOI:https://doi.org/10.1063/1.4928426· OSTI ID:22492298

Ravikumar, Patta; Kisan, Bhagaban

We report systematic investigations of structural, vibrational, resonance and magnetic properties of nanoscale NiO powders prepared by ball milling process under different milling speeds for 30 hours of milling. Structural properties revealed that both pure NiO and as-milled NiO powders exhibit face centered cubic structure, but average crystallite size decreases to around 11 nm along with significant increase in strain with increasing milling speed. Vibrational properties show the enhancement in the intensity of one-phonon longitudinal optical (LO) band and disappearance of two-magnon band due to size reduction. In addition, two-phonon LO band exhibits red shift due to size-induced phonon confinement effect and surface relaxation. Pure NiO powder exhibit antiferromagnetic nature, which transforms into induced ferromagnetic after size reduction. The average magnetization at room temperature increases with decreasing the crystallite size and a maximum moment of 0.016 μ{sub B}/f.u. at 12 kOe applied field and coercivity of 170 Oe were obtained for 30 hours milled NiO powders at 600 rotation per minute milling speed. The change in the magnetic properties is also supported by the vibrational properties. Thermomagnetization measurements at high temperature reveal a well-defined magnetic phase transition at high temperature (T{sub C}) around 780 K due to induced ferromagnetic phase. Electron paramagnetic resonance (EPR) studies reveal a good agreement between the EPR results and magnetic properties. The observed results are described on the basis of crystallite size variation, defect density, large strain, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion. The obtained results suggest that nanoscale NiO powders with high T{sub C} and moderate magnetic moment at room temperature with cubic structure would be useful to expedite for spintronic devices.

• OSTI ID: 22492298
• Journal Information: AIP Advances, Vol. 5, Issue 8; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 2158-3226
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANTIFERROMAGNETIC MATERIALS
ANTIFERROMAGNETISM
COERCIVE FORCE
ELECTRON SPIN RESONANCE
FCC LATTICES
FERROMAGNETISM
MAGNETIC MOMENTS
MAGNETIC PROPERTIES
MAGNETIZATION
NANOPARTICLES
NANOSTRUCTURES
NICKEL OXIDES
OXIDATION
PHASE TRANSFORMATIONS
PHONONS
POWDERS
RED SHIFT
REDUCTION
RELAXATION
TEMPERATURE DEPENDENCE