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Maghemite (Fe 2 O 3, γ-Fe 2 O 3) is a member of the family of iron oxides. It has the same formula as hematite , but the same spinel ferrite structure as magnetite ( Fe 3 O 4 ) and is also ferrimagnetic .
It is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral maghemite. It is ferromagnetic and finds application in recording tapes, [12] although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide.
Maghemite is a polymorph of hematite (γ-Fe 2 O 3) with the same chemical formula, but with a spinel structure like magnetite. Large deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that have still, standing water, or mineral hot springs, such as those in Yellowstone National Park in North ...
Maghemite differs from magnetite in that all or most of the iron is in the trivalent state (Fe 3+) and by the presence of cation vacancies in the octahedral sites. Maghemite has a cubic unit cell in which each cell contains 32 oxygen ions, 21 1 ⁄ 3 Fe 3+ ions and 2 2 ⁄ 3 vacancies. The cations are distributed randomly over the 8 tetrahedral ...
Iron(II,III) oxide, or black iron oxide, is the chemical compound with formula Fe 3 O 4.It occurs in nature as the mineral magnetite.It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe 2 O 3) which also occurs naturally as the mineral hematite.
In addition to igneous rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake and marine sediments as both detrital grains and as magnetofossils. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite. [13]
Ferrite nanoparticles or iron oxide nanoparticles (iron oxides in crystal structure of maghemite or magnetite) are the most explored magnetic nanoparticles up to date.Once the ferrite particles become smaller than 128 nm [22] they become superparamagnetic which prevents self agglomeration since they exhibit their magnetic behavior only when an external magnetic field is applied.
Goethite and hematite (U-Th)/He geochronology yields ages between ca. 18 to 4 Ma for the ferruginization of the Yandi and Robe River CIDs. [1] [2] Although these ages agree with the generally accepted Miocene model age for the formation of the western Australian CIDs, [3] some researchers have questioned the validity of these ages on the basis of the authors' geologic sampling and statistical ...