Synthesis & Multiferroic Materials Flashcards
What is the Nèel temperature?
The critical ordering temperature at which antiferromagnetic ordering occurs. The characteristic temperature is set by the energy scale of its exchange interactions:
In antiferromagnetism what does the negative value of theta imply?
(Theta being the energy scale of the exchange interactions)
It implies the existence of a negative molecular field, causing neighbouring moments to anti align
In antiferromagnetism what does the negative value of theta imply?
(Theta being the energy scale of the exchange interactions)
It implies the existence of a negative molecular field, causing neighbouring moments to anti align
In AFM, the molecular field of the A sub lattice is equal in magnitude but opposite in direction to the B sub lattice magnetisation and vice versa. How do you use this to work out the total field experienced by a given moment?
How do we use the Curie law (replacing H by H-tot) to obtain the Curie-Weiss law For an AFM?
What does mean field theory predict about the magnetic susceptibility?
What is Pi type super exchange ?
What is Bragg’s law for constructive interference?
What characteristic of a neutron allows it to penetrate deeply into a material, and what information does X-ray and neutron diffraction provide ?
Unlike X-rays, the charge neutrality of a neutron means it can penetrate deeply into a material,and it is scattered by nuclear forces.
Neutron and X-ray diffraction provide complimentary structural information.
How does neutron diffraction give us information on the magnetic structure of a material?
Neutrons have a spin, therefore a magnetic moment. This interacts with unpaired electrons in a magnetic material
How are neutrons for scattering experiments produced ?
Either by nuclear fission or spallation (the break up of a bombarded nucleus into several parts)
What is a ferrimagnet?
Their magnetic moments are aligned anti parallel similar to AFM’s. However these magnetic moments are of different magnitudes so do not cancel completely..
What is the structure of a ferrite
(An important class of ferrimagnetic inorganic solids)
Normal vs inverse spinels (what spaces ions occupy,examples , and dominant interactions)
Where does the inverse spinel ferrite Fe3O4 occur in nature ?
As the mineral magnetite
What type of exchange interaction occurs between Fe3+ ions on octahedral and tetrahedral sites of magnetite
What type of exchange interaction occurs between Fe2+ and Fe3+ ions of neighbouring octahedral sites in magnetite?
