Room temperature ferromagnetism in CoO nanoparticles obtained from sonochemically synthesized precursors

Dutta, Dimple P.; Sharma, Garima; Manna, P. K.; Tyagi, A. K.; Yusuf, Salim

doi:10.1088/0957-4484/19/24/245609

Cited by 54 publications

(49 citation statements)

References 36 publications

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“…Probably both the moderately strong core-shell interface exchange coupling (evidenced by the large exchange bias observed in these systems [11][12][13]) and the small shell thickness contribute to make the effect more evident. The possible persistence of a magnetic moment in -Mn 2 O 3 above T C;shell and T N;core is not clear at present, although it could be related to oxygen vacancies in -Mn 2 O 3 , as has been proposed [43] for other transition metal oxides exhibiting persisting magnetic signal well above their corresponding transition temperatures [43][44][45].…”

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confidence: 81%

Magnetic Proximity Effect Features in Antiferromagnetic/Ferrimagnetic Core-Shell Nanoparticles

et al. 2009

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A study of ''inverted'' core-shell, MnO=-Mn 2 O 3 , nanoparticles is presented. Crystal and magnetic structures and characteristic sizes have been determined by neutron diffraction for the antiferromagnetic core (MnO) and the ferrimagnetic shell (-Mn 2 O 3 ). Remarkably, while the MnO core is found to have a T N not far from its bulk value, the magnetic order of the -Mn 2 O 3 shell is stable far above T C , exhibiting two characteristic temperatures, at T $ 40 K [T C ð-Mn 2 O 3 Þ] and at T $ 120 K [$T N ðMnOÞ]. Magnetization measurements are consistent with these results. The stabilization of the shell moment up to T N of the core can be tentatively attributed to core-shell exchange interactions, hinting at a possible magnetic proximity effect.

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confidence: 81%

Magnetic Proximity Effect Features in Antiferromagnetic/Ferrimagnetic Core-Shell Nanoparticles

et al. 2009

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“…The PLS and CDBS were measured simultaneously. About 1×10 6 and 4×10 6 total counts were collected for each lifetime and Doppler spectrum, respectively. Magnetic properties were measured by using vibrating sample magnetometer (VSM) of physical property measurement system (Quantum Design, PPMS).…”

Section: Methodsmentioning

confidence: 99%

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Chen¹,

Chen²,

Zhang³

et al. 2017

ECS J. Solid State Sci. Technol.

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Pure NiO nanoparticles were subjected to isochronal thermal treatments in open air from 100 to 1000 • C. X-ray diffraction (XRD) patterns indicate that all annealed samples exhibit a single phase of face-centered cubic (FCC) crystalline structure, obvious grain growth occurs only above 400 • C and the average crystallite size increases from 20 to 80 nm. X-ray photoelectron spectroscopy (XPS) shows that only very few amount of Ni 3+ and no impurity element have been found in the annealed samples. Positron annihilation measurements reveal that large number of Ni-vacancy defects exist in the grain surface region. These surface defects begin to recover after annealing above 400 • C, and most of them are removed at 1000 • C. Room temperature ferromagnetism is obviously observed for the samples annealed at 100 and 400 • C. The saturation magnetization gradually decreases with the increase of the annealing temperature, and it almost disappears at 800 and 1000 • C. The disappearance of ferromagnetism shows good coincidence with the recovery of Ni-vacancies. Our results suggest that the anomalous ferromagnetic behavior in NiO nanoparticles might be due to the surface Ni-vacancy defects instead of grain size effects. 2 It is well known that the bulk AF materials are magnetically compensated and have zero net magnetic moment in zero applied field, while fine particles of an AF material should display either weak ferromagnetism (FM) or superparamagnetism (SPM).3 Since Richardson and Milligan first reported anomalous magnetic properties in NiO nanoparticles, 4 ferromagnetic behaviors were found in an increasing number of AF nanomaterials. Consequently, it is important to investigate the magnetic mechanism of AF nanomaterials extensively. Among the various nanostructured AF transition metal monoxides, NiO has been widely investigated, because it is a unique metal-deficient p-type semiconductor presenting a wide band-gap (3.6-4.0eV), and its bulk form possesses a relatively high Néel temperature T N (523 K). As a consequence, it can cause high storage density of magnetic recording media due to allowing magnetic stability at very low volumes far above room temperature. 17 In the recent few decades, great efforts have been devoted to exploring the unexpected magnetic properties in NiO nanomaterials, such as large magnetic moments, enhanced coercivity, spin glass freezing and hysteretic loop shifts. However, up to now the underlying mechanism for the FM is still unclear. It has been reported that the FM might come from the surface and finite size effects, or a net magnetic moment probably arises from uncompensated spins. Several models, such as the two-sublattice model, 3 multi-sublattice model, 10 and core-shell model 9,12-14,18-24 have been used to illustrate the anomalous properties of NiO nanoparticles. However, different groups reported that * Electrochemical Society Fellow.z E-mail: czy2004hust@163.com; chenzq@whu.edu.cn; mascher@mcmaster.ca surface effects and size effects on the ferromagnetic properties of the nanomater...

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“…The former has been discussed for ZnO containing CuO-clusters [67]. Ferromagnetism is also known for pure CoO [103] or NiO [104] nanoparticles. Note that large saturation magnetization has been achieved for CoO nanoparticles in Ref.…”

Section: Hidden Secondary Phasesmentioning

confidence: 99%

Non‐DMS related ferromagnetism in transition metal doped zinc oxide

Potzger

Zhou

2009

Physica Status Solidi (b)

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We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can easily be confused with the formation of a ferromagnetic diluted magnetic semiconductor (DMS). We will focus on metallic as well as oxide precipitates and the difficulties of their identification.Comment: 24 pages, 22 figure

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Room temperature ferromagnetism in CoO nanoparticles obtained from sonochemically synthesized precursors

Cited by 54 publications

References 36 publications

Magnetic Proximity Effect Features in Antiferromagnetic/Ferrimagnetic Core-Shell Nanoparticles

Magnetic Proximity Effect Features in Antiferromagnetic/Ferrimagnetic Core-Shell Nanoparticles

Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study

Non‐DMS related ferromagnetism in transition metal doped zinc oxide

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