Magnetic Nanoparticles

Question 1

What are the 4 ways we make nanoparticles?

Answer 1

1) Chemical based techniques 2) Physical vapour deposition 3) Electron beam lithography 4) Exploiting nature

Question 2

Give an example of a chemical based technique to make nanoscale objects

Answer 2

Nanoparticle synthesis in solutions

Question 3

Give an example of a physical vapour depositon technique used to make nanoscale objects

Answer 3

atom-by-atom approach, for example nanofilms, nanoclusters, nanodiscs

Question 4

Give an example of an electron beam lithography technique used to make nanoscale objects

Answer 4

‘carving’ nanostructures from larger scale material

Question 5

Give an example of exploiting nature in making nanoscale objects

Answer 5

iron oxide nanoparticles from magnetotactic bacteria

Question 6

Why do we use MAGNETIC nanoparticles?

Answer 6

Because we can use magnetic fields to control nanoparticles!

Question 7

What can we use magnetic field to DO to the particles? 6 things

Answer 7

1) positioning or targeting 2) mechanical stimulation of cells 3) generation of heat 4) separating mixtures 5) assays/biomarkers 6) imaging detection

Question 8

Draw out the life cycle of a magnetic nanoparticle

Answer 8

Go girl g g go go gooo

Question 9

What are the four forms of magnets?

Answer 9

1) paramagnets 2)ferro/ferrimagnets 3)superparamagnets 4)diamagnets

Question 10

Define a ferro/ferrimagnet

Answer 10

There is a strong attraction between N and S of magnets. Easy to draw too ;)

Question 11

Define a diamagnet

Answer 11

There is a weak repulsion between N and N. Repelled by magnetic fields

Question 12

Define a paramagnet

Answer 12

Weak attraction between N/S

Question 13

What is a diamagnet repelled by?

Answer 13

magnetic fields

Question 14

What is the equation for magnetic susceptibility and what do the constituents mean?

Answer 14

X = M/H - M is the magnetisation of the substance and H is the applied magnetic field

Question 15

How can we determine the magnetic nature of a substance?

Answer 15

By measuring how the magnetisation of the substance (M) varied in an applied magnetic field (H). Magnetic susceptibility equation.

Question 16

What is a paramagnet attracted by?

Answer 16

An externally applied magnetic field.

Question 17

Talk about how a paramagnet is made, particle wise.

Answer 17

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.

Question 18

Do paramagnets retain any magnetisation in the abs of an externally applied magnetic field?

Answer 18

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

Question 19

What is the link between paramagnets and absolute 0?

Answer 19

Some paramagnets retain magnetisation at absolute 0 - this is known as being paramagnetic at ground state.

Question 20

What is the magnetisation like for a paramagnet in the presence of a field?

Answer 20

Small, because only a few spins are oriented by the field.

Question 21

Describe how ferromagnetism comes about

Answer 21

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

Question 22

What kind of a magnetic susceptibility do ferromagnets have?

Answer 22

large

Question 23

Describe diamagnets and their workings

Answer 23

When a magnetic field is applied, a small opposing magnetisation occurs. Small magnetic susceptibility.

Question 24

What kind of a magnetic susceptibility do diamagnets have?

Answer 24

SMall

Question 25

What is antiferromagnetisation?

Answer 25

The spins are coupled so no net magnetisation

Question 26

What is ferrImagnetism?

Answer 26

anti-aligned but unequal size, so have a similar behaviour to ferromagnets

Question 27

Is ferro/ferrimagnetisation reversible?

Answer 27

No. They end up in a hysterisis loop.

Question 28

What is hysterisis?

Answer 28

A non-linear link between M and H.

Question 29

What is Dc?

Answer 29

The critical diameter for 1 magnetic domain, this is material dependent. <Dc is superparamagnetic

Question 30

What is remanence?

Answer 30

Residual magnetisation after application and removal of a magnetic field.

Question 31

Is remanence permanent or non-permanent?

Answer 31

Non permanent due to thermal instability

Question 32

How do we work out the relaxation time?

Answer 32

Using the materal constant K, the particle fvolume V and the temperature T

Question 33

What is the relaxation time of a collection of single domain particles?

Answer 33

The time it takes for the remanence to decay to 0

Question 34

What is a blocked state?

Answer 34

When the relaxation time is longer than the measurement time

Question 35

What is a superparamagnetic state?

Answer 35

When the relaxation time is shorter than the measurement time. A superparamagnet is a single giant domain.

Question 36

Define a superparamagnet

Answer 36

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.