Exchange bias and phase transformation in α-Fe2O3/Fe3O4 nanocomposites

Liu, X.H.; Cui, Weibin; Liu, W.; Zhao, Xinguo; Li, Didi; Zhang, Z.D.

doi:10.1016/j.jallcom.2008.07.097

Cited by 23 publications

(12 citation statements)

References 30 publications

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“…Recently, it has been investigated widely in diverse heterostructure systems, for example, layered films, fine particles, and inhomogeneous materials without clearly defined magnetic regions, both theoretically and experimentally [4][5][6]. Accordingly, the interfaces of material system are not only FM/AFM, but also FM/spin-glass (SG), AFM/ferrimagnetic (FI) and FI/FI [7][8][9]. Additionally, EB effect usually arises in such systems, in which T N is lower than the Curie temperature (T C ).…”

Section: Introductionmentioning

confidence: 99%

Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

et al. 2015

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NiCr 2 O 4 /NiO ceramic has been synthesized successfully through co-precipitation method to study the magnetic properties. Field cooling (FC) magnetic hysteresis loops measured at low temperature show significant shift in both coercive field and remnant magnetization. It has been plotted that the exchange bias (EB) field can be as large as 11.86 kOe at 10 K followed with an enhanced coercive field. The variation of EB field and shift of remnant magnetization after FC processes shows a regular tendency with increasing temperature and cooling field. Known as training effect, the EB behavior also presents a strong dependence on loop cycle. The cycle dependence of large EB field, vertical shift of magnetization, and coercive field at low temperature can be ascribed to the pinned spins in spin-glass-like (SGL) phase of the system interface. The SGL phase has been proved by Almeida-Thouless line and high field relaxation effect. The disorder structure is responsible for the frustration interface and the formation of SGL phase in the interface.

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Section: Introductionmentioning

confidence: 99%

Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

et al. 2015

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“…Work on similar oxide multilayers has also sometimes reported anomalous magnetic moments in the antiferromagnet layers 25 or double-step hysteresis loops. 26 This elicits a second possibility that uncompensated spins or foreign phases embedded within the antiferromagnet, such as Fe 25 or Fe 3 O 4 clusters, 27 may also play a part in the observed exchange bias. To better understand the mechanism for exchange bias, we investigated a nanocrystalline permalloy/hematite bilayer using a depth-sensitive magnetic neutron scattering technique.…”

Section: Introductionmentioning

confidence: 99%

Exchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry

et al. 2012

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We investigated a hematite α-Fe2O3/permalloy Ni80Fe20 bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the Néel temperature of bulk α-Fe2O3 is known to be very high (860 K), we attribute the lowtemperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5-1.0 μB per Fe atom within a depth of 1-2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains. We investigated a hematite α-Fe 2 O 3 /permalloy Ni 80 Fe 20 bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the Néel temperature of bulk α-Fe 2 O 3 is known to be very high (860 K), we attribute the low-temperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5-1.0 μ B per Fe atom within a depth of 1-2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains.

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“…Therefore, the particle size reduction has significantly affected the magnetic properties of natural Fe 2 O 3 based iron ore. The coercivity of as-milled powders increased with milling time; this was attributed to the introduction of defects, oxide, and other contamination during the milling [9,10]. Obviously, the enhanced magnetic properties can be explained as the presence of a surface layer with high concentration of defects induced by the milling process [11].…”

Section: Resultsmentioning

confidence: 99%

Magnetic Behavior of Natural Fe₂O₃ from Lhoong Iron Ore Mining Area, Aceh Province, Indonesia

2013

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The mineral composition and magnetic behavior of nano-Fe 2 O 3 of iron ore from Lhoong mining area, Aceh province, were studied. The iron ore was prepared by mechanical milling method. The mineral and chemical compositions of samples were investigated by XRD and XRF analysis tests. The XRF test showed that the Lhoong iron ore contains Fe 2 O 3 (93.88%) in association with other isomorphous impurities, such as SiO 2 , MnO, and Al 2 O 3 , in varying proportions. Compared to XRD results, it was consistent with XRF; the phase compositions of iron ore were mainly hematite (Fe 2 O 3 ). The XRD revealed that hematite was the major mineral component in the Lhoong iron ores. SEM observation showed fine crystalline structure of Lhoong iron ore after the milling process. The main mineral morphology was microcrystalline in agglomerate forms. The magnetic properties of the samples after milling showed the increasing in the remanent (B ) and coercivity (H ). This increasing can be explained that nano-Fe 2 O 3 phase after milling for 20 hours plays an important role in the magnetic behavior of Lhoong iron ore. It is understood that the longer milling time is sufficient to complete the transformation of hematite (Fe 2 O 3 ) to magnetite (Fe 3 O 4 ).

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Exchange bias and phase transformation in α-Fe2O3/Fe3O4 nanocomposites

Cited by 23 publications

References 30 publications

Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

Exchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry

Magnetic Behavior of Natural Fe₂O₃ from Lhoong Iron Ore Mining Area, Aceh Province, Indonesia

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Exchange bias and phase transformation in α-Fe2O3/Fe3O4 nanocomposites

Cited by 23 publications

References 30 publications

Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

Giant exchange bias behavior and training effect in spin-glass-like NiCr2O4/NiO ceramics

Exchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry

Magnetic Behavior of Natural Fe2O3 from Lhoong Iron Ore Mining Area, Aceh Province, Indonesia

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Magnetic Behavior of Natural Fe₂O₃ from Lhoong Iron Ore Mining Area, Aceh Province, Indonesia