Knight shift is an NMR quantity that consist of two components, K =Kspin+Korb.
What do these terms mean? Do they have temperature dependence? Can I observe both components of K at low temperatures?
I try answering point wise but very briefly:
[A]The Knight shift is a shift in NMR frequency of a paramagnetic substance [Walter D.Knight;1949].
[B]It arises from two sources:
(i) Pauli paramagnetic spin susceptibility
(ii) the s-component wavefunctions at the nucleus.
[C] Knight shift is given by K = Hhf/H = AχH/H ～Aχ.
The relation is derived as:
NMR shift originates from thermal average value of Hhf
=A
Since is expressed by
(thermal average value of electron magnetization),
=A～A (=AχH0)
Knight shift is given by K = Hhf/H = AχH/H ～Aχ
[D] In a way,
K is proportional to χ.
[E] As :
χ total[T]=χspin(T)+χorb+・・・+χimpurity
so will be value of K as:
Ktotal(T)=Kspin(T)+Korb
implying contributions from spin motion as well as the orbital motion because an electron has two types of motions and both contributes to the magnetism; no matters that the orbital motion contributes to a lesser extent.
[F] As Kspin is dependent upon the temperature, so should be Ktotal.
[G] Again, it can be observed at all temperature; of course its magnitude will be different because paramagnetism is dependent upon temperature.
The short answer is NO in simple metals and most intermetallic compounds which show pauli paramagnetism. Here, you might want to know that Knight shifts in Pd and possiblly in Pt are temperature dependent due to core polarization mechanism.
In some intermetallic compounds such as semimetals and narrow gapped semiconductors , Knight shifts can be strongly temperature dependent. Spin-orbit enhanced orbital magnetism might also explains the temperature dependence of Knight shifts in heavy metals such as Hg and Pb. We can dicuss this point further later. In rare earth containing (Ce, Pr, ..., Yb) compounds, Knight shifts are also temperature dependent. This can be well explained by the existence of localized magnetic moment.
In short, whether Knight shifts are temperature dependent or not, that depends on the mechanism that contributes to the observed NMR shifts.
Article NMR investigation of atomic and electronic structures of hal...
Dear Dr. Witter thanks a lot for your clear and brief explanation. And Dr. Sehgal,
thanks for your formulation.
Dear Dr. Xi,
Thanks for providing article and your answer.
YPdBi and YPtBi have different shifts that observed in the spectra.
Do you expect that platinum takes place of palladium? {at (1/4, 1/4, 1/4) or somewhere?}
In general I derived that Knight shift mainly depends on :
i) interaction of s-state wave functions
ii) Pauli paramagnetism
and
temperature dependence is directly related with the transport mechanism that your sample exhibits.
Kindly regards.
During this time, I could learn a bit more regarding K.
[1] The increase in χ at low temperature is due to magnetic impurities.
[2] If we plot a graph between K(%) and χ( emu/g) [χ along X-axis and K( %) along Y-axis], we get line passing through the center whose slope will give hyperfine coupling constant(Ahf) which can be compared with experimentally obtained Ahf value.
[3] K is related to spin lattice relaxation time T1 as:
1/ T1TK^2= S
Which is called Korringa relation[ T1T is constant].
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