Abstract
M.Sc.
When a pure chromium single crystal is cooled through its Néel temperature, it undergoes a
paramagnetic to a multi-wave vector incommensurate spin-density-wave magnetic transition.
Should a chromium single crystal be cooled through its Neel temperature in the presence of a
strong enough magnetic field, 4-5 T, then all the spin-density-wave vectors that occur as it undergoes
the paramagnetic to incommensurate spin-density-wave magnetic transition, are forced
to be aligned parallel to the direction of the applied magnetic field, producing what is called
a single spin-density-wave wave vector state in the crystal. The single spin-density-wave wave
vector state will remain in the crystal when the magnetic field is removed providing the crystal
is not heated above its Neel temperature. If the crystal when in the single spin-density-wave
wave vector state is orientated so that the single spin-density-wave wave vector is aligned perpendicular
to the direction of an applied magnetic field, then the spin polarisation vectors of the
magnetic moments will align themselves so that they are perpendicular to the applied magnetic
field and perpendicular to the single wave vector, producing what is called a single spin-densitywave
wave vector and single spin polarisation vector state in the crystal. There is a difference
in value between the elastic constants measured when a chromium single crystal is in the single
spin-density-wave wave vector state to the elastic constants measured when the crystal is in the
multi-wave vector spin-density-wave state.When pure chromium is alloyed with other materials the topology of the Fermi surface is changed
resulting in some of the alloys being able to undergo paramagnetic to commensurate spin-densitywave
magnetic transitions, as well as being able to undergo commensurate spin-density-wave to
incommensurate spin-density wave transitions. This study makes use of a magnetic field of
strength 4.5 Tin an attempt to produce a single spin-density-wave wave vector state in a Cr +
0.3 at.% Ru and a Cr + 1.6 at.% Si single crystals. Both single crystals undergo paramagnetic
to commensurate spin-density-wave transitions when cooled through their, respective Neel temperatures,
as well as the Cr + 0.3 at.% Ru single crystal being able to undergo a commensurate
spin-density-wave to an incommensurate spin-density-wave transition if cooled further, down to
77 K, well below it's Neel temperature. The effects of the applied magnetic field on the Cr + 0.3
at.% Ru and Cr + 1.6 at.% Si single crystals was determined by measuring the elastic constants
of the respective crystals.