SEM 2 PT3 Flashcards
What is a magnetic moment
Measure of an object’s tendacy to align with a magnetic field
What are diamagnets
Materials with no pre-existing magnetic moments
Why are superconductors perfect diamagnetic materials?
Induced magnetisation cancels applied B-field leading to 0 B-fields in bulk superconductor
What is paramagnetic behaviour?
B-field applied to material with pre-existing magnetic moment and induces a net alignment of magnetic moments in the direction of applied field.
What is ferromagnetism?
Magnetic moments tend to align parallel to each other to produce a strong magnetisation even in the absence of applied magnetic field
What is anti-ferromagnetism?
Materials the moment directions alternate giving zero net magnetisation
What is magnetic moments due to
unpaired electron spins or orbital electron motion
Is magnetic susceptability positive or negative for paramagnets and diamagnets
Paramagnets are positive
Diamagnets are negative
Why do diamagnets occur in all materials
Due to magnetic moments induced in a material due to applied B-fields
Applied B-Fields induces orbital moments in atoms of material
and material is conducting thenthe
Net orbital moments in conducting electrons
Induced moments and magnetisation is in opposite direction to applied magnetic field therefore magnetisation is negayive
How paramagnetism words in materials with pre-exisitng magnetic moments
W/O an applied B-fields, moments are oriented randomly giving 0 magnetisation
When magnetic field is applied moments align in direction of magnetic field - giving net magnetisation which increases applied field
At Room temp - magnetisation increases linearly w applied b-fields
For material where interaction between magnetic moment is weal what is the low magnetic field susceptibility dependant on?
inversely on temperature
At very low
temperatures and very high magnetic fields M(H) becomes
non-linear and M ultimately reaches a maximum value,
the saturation magnetisation, Msat, when all the moments
are fully aligned with the applied field.
How do ordered magnetic states arise
interactions between individual magnetic magnetic moments in a material
How ferromagnetis work
Spotaneous parallel alignments of moments with M not equal to 0 and H=0
How do materials induce an EMF
Increasingly applying B-field from 0
What is Lenz law
Resulting electric currents produce a B-fields of opposite sign to applied field.
Origin of diamagnetism at atomic level
What is magnetic moment due to
orbital motion is induced the resulting magnetic moments persist even when applied field is constant.
Magnetic moment due yo planar conducting loop carrying current
How to calculate susceptibility
Calculate mean square distance of an electron from the z- axis of a particular atom
How many energy levels does an applied magnetic field produce
(2𝐽 + 1)
What is the Curie temperature
temperature above which the spontaneous magnetization vanishes
in ferro magnetisx,when are the energies of the neighbouring atoms lower
When in parallel
What are exchange interactions
dependance of total energy on relative orientation of spins
What are magnons
vibrational modes of magnetic moments
In the absence of a magnetic field, what determines the direction of moments points
Magnetic anisotropy - favouring onr or a number of lower energy orientations of magentisation
Magneto-crystalline anisotropy- specific crystal structures
shape anisotropy- non-spherical samples
strain anisotropy - samples with uniaxial strain
What is Strain Anisotropy
atoms of a solid being closed together along specific direction - leading to anisotropic exchange and spin-orbit coupling
