Dilute-defect magnetism: Origin of magnetism in nanocrystalline<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>CeO</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

Fernandes, V.; Mossanek, R. J. O.; Schio, P.; Klein, J. J.; Oliveira, A. J. A. de; Ortiz, W.A.; Mattoso, N.; Varalda, J.; Schreiner, W. H.; Abbate, M.; Mosca, D. H.

doi:10.1103/physrevb.80.035202

Cited by 136 publications

(115 citation statements)

References 37 publications

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“…We found the same behavior, i.e., pristine nanosheets are nonmagnetic and Sn vacancies in nanosheets induce magnetism. Note that previous theoretical calculations have shown that the inclusion of the U term does not change the magnetic moments caused by vacancies 29,30 . Such term will have some effect on the electronic density of states 31 , but it will not change the main conclusion drawn here.…”

mentioning

confidence: 81%

Intrinsic magnetism in nanosheets of SnO2: A first-principles study

Rahman

García‐Suárez

Morbec

2013

Journal of Magnetism and Magnetic Materials

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We propose intrinsic magnetism in nanosheets of SnO2, based on first-principles calculations. The electronic structure and spin density reveal that p orbitals of the oxygen atoms, surrounding Sn vacancies, have a non itinerant nature which gives birth to localized magnetism. A giant decrease in defect formation energies of Sn vacancies in nanosheets is observed. We, therefore, believe that native defects can be stabilized without any chemical doping. Nanosheets of different thicknesses are also studied, and it is found that it is easier to create vacancies, which are magnetic, at the surface of the sheets. SnO2 nanosheets can, therefore, open new opportunities in the field of spintronics.The quest for room temperature (RT) ferromagnetism in diluted magnetic semiconductor (DMS), where transition metal (TM) (magnetic) impurities are doped into semiconductor hosts, e.g., Mn in GaAs 1 , has motivated many theoretical and experimental studies. TM impurities were found however to produce intrinsic defects which limit its application in the field of spintronics at RT. Next ideal candidates for RT applications in spintronics are oxide-based DMS systems, which not only have high T C , but also large magnetic moments 2 . Such oxide-based DMS also faced challenges, i.e., the determination of the origin of their magnetic properties and the control of these properties in oxides. The difficulties arise from the presence of defects (cation/anion vacancies), which can be beneficial for magnetism but whose degree of influence is not completely understood. It is believed that some oxides show magnetism without any magnetic impurities 3-7 mainly due to cation vacancies. The role of vacancies (either cation or anion) in magnetism can not then be ignored 8 . For the last few years extensive work (both experimental and theoretical) has been done to understand the origin of magnetism in materials with defects. Some of these new discoveries also made possible to have magnetism in nonmagnetic insulators/semiconductors doped with light elements 9-11 . Very recently, some of us found that C can also induce magnetism in SnO 2 9 , and later on this new theoretical idea was shown experimentally by Hong et al 12 . Therefore, it is now believed that magnetism can exist either in materials with vacancy or light elementsdoped systems 3-7,9-11 . Usually, cation vacancies, which are a source of magnetic moments, have large formation energies and it is not easy to produce them experimentally. Therefore, there remains an open and challenging question how intrinsic defects (vacancies) can be stabilized in nonmagnetic materials. Here, we find a new way of stabilizing defects in SnO 2 . We show that intrinsic defects can be easily stabilized by reducing the dimensionality of SnO 2 . This is a very unique way of reducing the formation energy of vacancies without any alien impurities. Note that there are several experimental reports on the fabrication of nanostructured SnO 2 13-17 . Beltran et al. 18 , have discussed the thermodynamic stability of nanost...

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confidence: 81%

Intrinsic magnetism in nanosheets of SnO2: A first-principles study

Rahman

García‐Suárez

Morbec

2013

Journal of Magnetism and Magnetic Materials

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“…From experimental and theoretical studies, it seems that the FM is attributed to oxygen or Hf vacancies [8]. Moreover, theoretical calculations have suggested that the FM can be induced by cation vacancies in TiO 2 , ZnO, and SnO 2 [9][10][11][12], or by anion vacancies in CeO 2 [13]. Room temperature FM has also been found in metal oxides such as TiO 2 , ZnO, CeO 2 , and SnO 2 which is due to oxygen vacancies and quantum confinement effects according to the experimental results [14][15][16][17][18].…”

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confidence: 99%

Revealing a room temperature ferromagnetism in cadmium oxide nanoparticles: an experimental and first-principles study

et al. 2015

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“…In several works devoted to RT-FM in CeO 2 , the high mobility of oxygen, and the consequent facility to create oxygen vacancies, is suggested as the cause for this peculiar behavior as this process would promote the presence of magnetic Ce 3+ ions 3,15 .…”

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confidence: 99%

“…CeO 2 -based systems have been thoroughly studied after the discovery of RT-FM on both pure 6,7,8,9,10 and slightly doped 11,12,13,14 samples. A large amount of effort has been devoted to the study of thin films 3,12,13,15,16,17,18,19 (see also references in [1]) while few works have focused on powdered samples 8,9,10,11,14 .…”

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confidence: 99%

Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles

Sacanell

Paulin

Ferrari

et al. 2012

Applied Physics Letters

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We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO 2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500ºC and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time Among the various oxides displaying this particular behavior is CeO 2 , which in bulk is a diamagnetic insulator with proven capability as an oxygen ion conductor when doped with trivalent Sm or Gd ions 5 . CeO 2 -based systems have been thoroughly studied after the discovery of RT-FM on both pure 6,7,8,9,10 and slightly doped 11,12,13,14 samples. A large amount of effort has been devoted to the study of thin films 3,12,13,15,16,17,18,19 (see also references in [1]) while few works have focused on powdered samples 8,9,10,11,14 .The use of powders is advantageous because the typically low magnetic signals of these systems can easily be enhanced just by increasing the quantity of the sample. In addition, the surface to volume ratio of the sample can be adjusted simply by performing adequate thermal treatments and this is particularly convenient as the surface is usually the preferred location of point defects.In several works devoted to RT-FM in CeO 2 , the high mobility of oxygen, and As magnetic signals in DMOs are typically small, extreme care must be taken during the synthesis procedure and handling of the samples to avoid contamination, and it is also important to carry out methodological studies to discard the possible influence of spurious magnetic impurities. In this work we performed a systematic study of the magnetic properties of CeO 2 nanopowders with particular focus on the influence of oxygen vacancies in both pure and doped samples. We show that an annealing process in vacuum can induce RT-FM in doped samples and paramagnetic (PM) behavior in pure samples. In all cases, this magnetic behavior can be erased by re-oxidation, ruling out segregation as responsible for the magnetic signal. The use of nanostructures allows us to enhance the surface to volume ratio, thus increasing the relative concentration of defects compared to bulk samples.Pure and Co-doped CeO 2 powders were synthesized by the Liquid-Mix method using 99.99% Ce(NO 3 ):6H 2 O and Cobalt(II) nitrate hexahydrate as reagents. All samples were calcined in air at 300ºC. Additional thermal treatments were performed at 500ºC, both in air at atmospheric pressure and in vacuum, using a mechanical pump to reach a pressure of around 4.10 -2 mbar, with dwell times between 4 and 30 hs. Samples were labeled with a two-number code denoting the atomic percentage of Co (x), and the dwell time of the vacuum treatment (dwt) in hours, namely x-dwt. Magnetic measurements were performed in a Versalab TM VSM from Quantum Design. X-ray diffraction data was obtained at the ID27 beamline of the European Synchrotron Radiation ...

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Dilute-defect magnetism: Origin of magnetism in nanocrystallineCeO2

Cited by 136 publications

References 37 publications

Intrinsic magnetism in nanosheets of SnO2: A first-principles study

Intrinsic magnetism in nanosheets of SnO2: A first-principles study

Revealing a room temperature ferromagnetism in cadmium oxide nanoparticles: an experimental and first-principles study

Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles

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