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Classes of Magnetic Materials (Paramagnetism (some atoms or ions material…
Classes of Magnetic Materials
origin of magnetism lies in the orbital and spin motions if electrons
the main distinction is that in some materials there is no collective interaction of atomic magnetic moments(diamagnetism and paramagnetism)
other materials have a very strong interaction between atomic moments
Ferro, ferri, and antiferromagnetism exhibits long-range magnetic order below a certain critical temperature.
ferromagnetic and ferrrimagnetic material are consider as magnetic and the others are consider as nonmagnetic
Diamagnetism
fundamental property of all matter due to non-cooperative behaviour of orbiting electrons when exposed to an applied magnetic field.
have no net magnetic moments
when exposed to a field, negative magnetization is produced, thus the susceptibility is negative
susceptibility is independent of temperature
well-known substances in units of 10e-8 m^3/kg; Quartz(SiO2), Calcite(CaCO3), water
Paramagnetism
some atoms or ions material have a net magnetic moments due to unpaired electrons in partially filled orbitals
magnetization is zero when field is remove(individual magnetic moments do not interact magnetically)
a partial alignment of the atomic magnetic moments in direction of fields, resulting a net positive magnetization and susceptibility
the efficiency of the field opposed the randomizing effect of temperature
obey Curie Law
if temperature very low (<<100k) or field is very high the paramagnetic susceptibility is independent of the applied field
many iron bearing minerals are paramagnetism at room temperature
Montmorillonite(clay), Biotite(silicate),Pyrite(sulfide)
paramagnetic correction maybe needed if the concentration of magnetite is very small
Ferromagnetism
atomic moment in these materials exhibit very strong interactions
the interactions are produced by electronic exchange forces
parallel or antiparallel alignment of atomic moments are produced
force exchange is quantum mechanical phenomenon due to relative orientation of the spins of two electron
exhibit parellel alignment of moments resulting large net magnetization even no magnetic field
distinct characteristics of ferromagnetic materials are spontaneous magnetization and the existence of magnetic ordering temperature
Spontaneous Magnetization
the net magnetization that exists inside a uniformly magnetized microscopic volume in the absence of field
at 0K it's dependent on the spin magnetic moments of electrons
saturation magnetization is the maximum induced magnetic moment that can be obtained in a magnetic field (Hsat)
the difference between spontaneous magnetization and the saturation magnetization(intrinsic property) has to do with magnetic domains
as compared to paramagnetic materials, the magnetization in ferromagnetic materials is saturated in moderate magnetic fields and at high temperature
Curie Temperature
below Curie Temperature, ferromagnet is ordered and above it, disordered.
the saturation magnetization goes to zero at Curie Temperature
an intrinsic property and is a diagnostic parameter that can be used for mineral identification.
Hysteresis
retain the memory of an applied field once it is removed
hysteresis parameter dependent on grain size, domain state, stresses and temperature
This is reverse field which the saturation is reduce remanence to zero when applied and then removed. field.
Ferrimagnetism
more complex forms of magnetic ordering
the magnetic structure is composed of two magnetic sublattices seperated by oxygens
indirect or super-exchange interactions mediated by oxygen anions.
exhibits all the hallmarks of ferromagnetic behaviour
ferro- and ferrimagnets have very different magnetic ordering
Magnatite is well known ferrimagnetic material
Crystal structure of Magnetite
Magnetite, Fe3O4 crystallizes with the spinel structure
the gaps come in two flavors i) tetrahedral site :Fe ion is surrounded by four oxygen; ii)Octahedral site: Fe ion is surrounded by six oxygen
spin on sublattice A are anti parallel to those on the B sublattice
this particular arrangement of cations on the A and B sublattice is called an inverse spinel structure
Antiferromagnetism
if the A and B sublattice moments are exactly equal but opposite, the net moment is zero
about the Néel temperature, the susceptibility obeys the Curie-Weiss law for paramagnets but with a negative intercept indicating negative exchange interactions
Crystal Structure of Hematite
Hematite crystallizes the corundum structure with oxygen ions in an hexagonal close packed frame work
Above -10 degree C, the spin moments lie in the c-plan but slightly canted produce weak spontaneous magnetization within c-plan
below -10 degree C, direction of antiferromagnetism changes and become parallel to the c-axis
Hematite becomes perfect antiferromagnet since no spin canting
spin-flop transition is called Morin transition
