Magnetic Nanoparticles Flashcards
What are the 4 ways we make nanoparticles?
1) Chemical based techniques 2) Physical vapour deposition 3) Electron beam lithography 4) Exploiting nature
Give an example of a chemical based technique to make nanoscale objects
Nanoparticle synthesis in solutions
Give an example of a physical vapour depositon technique used to make nanoscale objects
atom-by-atom approach, for example nanofilms, nanoclusters, nanodiscs
Give an example of an electron beam lithography technique used to make nanoscale objects
‘carving’ nanostructures from larger scale material
Give an example of exploiting nature in making nanoscale objects
iron oxide nanoparticles from magnetotactic bacteria
Why do we use MAGNETIC nanoparticles?
Because we can use magnetic fields to control nanoparticles!
What can we use magnetic field to DO to the particles? 6 things
1) positioning or targeting 2) mechanical stimulation of cells 3) generation of heat 4) separating mixtures 5) assays/biomarkers 6) imaging detection
Draw out the life cycle of a magnetic nanoparticle
Go girl g g go go gooo
What are the four forms of magnets?
1) paramagnets 2)ferro/ferrimagnets 3)superparamagnets 4)diamagnets
Define a ferro/ferrimagnet
There is a strong attraction between N and S of magnets. Easy to draw too ;)
Define a diamagnet
There is a weak repulsion between N and N. Repelled by magnetic fields
Define a paramagnet
Weak attraction between N/S
What is a diamagnet repelled by?
magnetic fields
What is the equation for magnetic susceptibility and what do the constituents mean?
X = M/H - M is the magnetisation of the substance and H is the applied magnetic field
How can we determine the magnetic nature of a substance?
By measuring how the magnetisation of the substance (M) varied in an applied magnetic field (H). Magnetic susceptibility equation.
What is a paramagnet attracted by?
An externally applied magnetic field.
Talk about how a paramagnet is made, particle wise.
Thermal motion randomises spin orientations, so paramagnets do not retain any magnetisation in the absence of an externally applied magnetic field, however PM materials have permanent dipoles in abs of mag field due to unpaired electrons just no direction bc of thermal motion. Magnetic field dipoles align with field, leading to movement in direction of applied field.
Do paramagnets retain any magnetisation in the abs of an externally applied magnetic field?
No, they retain their dipoles as they are perm due to unpaired electrons, but their movemnt is randomised due to thermal instability so NO magnetisation
What is the link between paramagnets and absolute 0?
Some paramagnets retain magnetisation at absolute 0 - this is known as being paramagnetic at ground state.
What is the magnetisation like for a paramagnet in the presence of a field?
Small, because only a few spins are oriented by the field.
Describe how ferromagnetism comes about
After the events described in paramagnetism, if the energy exchange between dipoles is great enough, this results in a ferromagnet - a permanant magnet. These have a large magnetic susceptibility
What kind of a magnetic susceptibility do ferromagnets have?
large
Describe diamagnets and their workings
When a magnetic field is applied, a small opposing magnetisation occurs. Small magnetic susceptibility.
What kind of a magnetic susceptibility do diamagnets have?
SMall
What is antiferromagnetisation?
The spins are coupled so no net magnetisation
What is ferrImagnetism?
anti-aligned but unequal size, so have a similar behaviour to ferromagnets
Is ferro/ferrimagnetisation reversible?
No. They end up in a hysterisis loop.
What is hysterisis?
A non-linear link between M and H.
What is Dc?
The critical diameter for 1 magnetic domain, this is material dependent. <Dc is superparamagnetic
What is remanence?
Residual magnetisation after application and removal of a magnetic field.
Is remanence permanent or non-permanent?
Non permanent due to thermal instability
How do we work out the relaxation time?
Using the materal constant K, the particle fvolume V and the temperature T
What is the relaxation time of a collection of single domain particles?
The time it takes for the remanence to decay to 0
What is a blocked state?
When the relaxation time is longer than the measurement time
What is a superparamagnetic state?
When the relaxation time is shorter than the measurement time. A superparamagnet is a single giant domain.
Define a superparamagnet
Similar to a paramagnet but a higher magnetic susceptibilty. The magnetic field aligns with the WHOLE particle moments, which is many thousands of spin moments. It’s highly susceptible to magnetic fields and has 0 remanence. Relaxation times can be well matched to AC field frequencies for magnetic hyperthermia.
