Title: Summary Magnetism

Choose the correct statement.

- The magnetic moment of an electron is either +µB or -µB (where µB is the Bohr magneton) depending on whether it is down or up spin. (correct)
- The magnetic moment of an electron is either +µB or -µB (where µB is the Néel magneton) depending on whether it is down or up spin.

- The Pauli Principle states that the total electronic wavefunction must be antisymmetric with respect to the interchange of two electrons. (correct)
- The Pauli Principle states that the total electronic wavefunction must be symmetric with respect to the interchange of two electrons.

- The magnetic exchange energy J has a role in explaining the magnetism of some molecules, as it favours the parallel configuration of spins. (correct)
- The magnetic exchange energy J has a role in explaining the magnetism of some molecules, as it favours the antiparallel configuration of spins.

- The ground state of atoms, ions or molecules can be magnetic when (i) 2J is larger than the energy difference between states, (ii) there is an odd number of electrons and (iii) for degenerate orbitals. (correct)
- The ground state of atoms, ions or molecules can be magnetic when (i) 2J is smaller than the energy difference between states, (ii) there is an even number of electrons and (iii) for non-degenerate orbitals.

- The term magnetoresistance refers to the change in electrical resistivity of a material when a magnetic field is applied. (correct)
- The term magnetoresistance refers to the change in thermal conductivity of a material when a magnetic field is applied.

- In general, d bands present a small energy cost to promote electrons into empty levels, and a large J as electrons are tightly bound. Therefore, d bands easily become magnetic. (correct)
- In general, s bands present a small energy cost to promote electrons into empty levels, and a large J as electrons are tightly bound. Therefore, s bands easily become magnetic.

- The origin of antiferromagnetic ordering in transition metal oxides is a phenomenon called superexchange, which is a consequence of the partial covalent bonding between the transition metal ion and the neighbouring oxygen ions. (correct)
- The origin of antiferromagnetic ordering in transition metal oxides is a phenomenon called double exchange, which is a consequence of the partial covalent bonding between the transition metal ion and the neighbouring oxygen ions.

- Antiferromagnetic ordering can be mesured by using neutron diffraction. (correct)
- Antiferromagnetic ordering can be mesured by using X-ray diffraction.

- The double exchange mechanism favours the parallel ordering of neighbouring ions and therefore ferromagnetism, as electrical conductivity can only take place in this situation. (correct)
- The double exchange mechanism favours the antiparallel ordering of neighbouring ions and therefore ferromagnetism, as electrical conductivity can only take place in this situation.

- In certain occasions, electrons may localize in a symmteric pattern on specific ion sites. This phenomenon is called charge ordering, and since the electrons are localized, the system becomes insulating. (correct)
- In certain occasions, electrons may localize in a symmteric pattern on specific ion sites. This phenomenon is called charge ordering, and since the electrons are localized, the system becomes a metal.