T-B, with thermally stable spins capable of pinning the Ni cores and giving rise to exchange bias. The investigated samples may thus be envisaged as being constituted of both isolated core-shell Ni-NiO nanoparticles as well as clustered ones, with T-B denoting the blocking temperature of the NiO shell of the isolated particles. (C) 2014 AIP Publishing LLC." /> T-B, with thermally stable spins capable of pinning the Ni cores and giving rise to exchange bias. The investigated samples may thus be envisaged as being constituted of both isolated core-shell Ni-NiO nanoparticles as well as clustered ones, with T-B denoting the blocking temperature of the NiO shell of the isolated particles. (C) 2014 AIP Publishing LLC."/>
 
Exchange bias beyond the superparamagnetic blocking temperature of the antiferromagnet in a Ni-NiO nanoparticulate system
authors Roy, A; De Toro, JA; Amaral, VS; Muniz, P; Riveiro, JM; Ferreira, JMF
nationality International
journal JOURNAL OF APPLIED PHYSICS
keywords MAGNETIC-PROPERTIES
abstract We report magnetic and exchange bias studies on Ni-NiO nanoparticulate systems synthesized by a two-step process, namely, chemical reduction of a Ni salt followed by air annealing of the dried precipitate in the temperature range 400-550 degrees C. Size of Ni and NiO crystallites as estimated from X-ray diffraction line broadening ranges between 10.5-13.5 nm and 2.3-4 nm, respectively. The magneto-thermal plots (M-T) of these bi-magnetic samples show a well developed peak in the vicinity of 130 K. This has been identified as the superparamagnetic blocking temperature "T-B" of NiO. Interestingly, all samples exhibit exchange bias even above their respective NiO blocking temperatures, right up to 300 K, the maximum temperature of measurement. This is in contrast to previous reports since exchange bias requires the antiferromagnetic NiO to have a stable direction of its moment in order to pin the ferromagnet (Ni) magnetization, whereas such stability is unlikely above T-B since the NiO is superparamagnetic, its moment flipping under thermal activation. Our observation is elucidated by taking into account the core-shell morphology of the Ni-NiO nanoparticles whereby clustering of some of these nanoparticles connects their NiO shells to form extended continuous regions of NiO, which because of their large size remain blocked at T>T-B, with thermally stable spins capable of pinning the Ni cores and giving rise to exchange bias. The investigated samples may thus be envisaged as being constituted of both isolated core-shell Ni-NiO nanoparticles as well as clustered ones, with T-B denoting the blocking temperature of the NiO shell of the isolated particles. (C) 2014 AIP Publishing LLC.
publisher AMER INST PHYSICS
issn 0021-8979
year published 2014
volume 115
issue 7
digital object identifier (doi) 10.1063/1.4866196
web of science category Physics, Applied
subject category Physics
unique article identifier WOS:000332042000024
  ciceco authors
  impact metrics
journal analysis (jcr 2019):
journal impact factor 2.286
5 year journal impact factor 2.138
category normalized journal impact factor percentile 54.87
dimensions (citation analysis):
altmetrics (social interaction):



 


Apoio

1suponsers_list_ciceco.jpg