Transcript A Microsoft Power Point File Used during the Presentation of the Paper at the National Symposium of the NMRS at the SIF:Indian institute of Science,Bangalore,INDIA during February 5-6,2003. This file consists of instructuons to Viewers of that PPT. file which were Included after the presentation before Uploading for the Internet-availablity

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Thursday, July 28, 2016
MR Symposium 05-02-2003
1
MR Symposia 2003 Presentation
5th February 2003
S.ARAVAMUDHAN
Department of chemistry
North Eastern Hill University , Shillong
Can HR PMR Provide a Further Insight
Concerning the Requirement of the
Spherical Shape of Lorentz Cavity?
Text of Abstract: CLICK here for hyperlink to slides 13 &14
Thursday, July 28, 2016
MR Symposium 05-02-2003
2
Bulk Susceptibility Effects
In HR PMR
SOLIDS
Liquids
Induced Fields
at the Molecular Site
Da= - 4/3
Single
Crystal
Single crystal
Spherical Shape
arbitray shape
Db= 2/3
Sphere
Lorentz
Thursday, July 28, 2016
cavity
MR Symposium 05-02-2003
3
A link to a Web Site containing Features of Demagnetzation
Factors Calculations
Click Here for the
consideration of Variety of
possibilities for the lattices and
site symmetries
i=ii /R3i [1-(3.RRi /R5i)]
LINK to
Demagnetization Effects
Graph
Size of the Cavity
and the choice of its
location in the
Specimen can be
varied to sample the
induced field over
the extent of the
specimen
Thursday, July 28, 2016
Magnetic
Field
-4/3 + 4/3
MR Symposium 05-02-2003
4
INDUCED FIELDS,DEMAGNETIZATION,SHIELDING
Induced Field inside a hypothetical Lorentz’ cavity within a specimen = H``
Shielding Factor = 
Demagnetization Factor = Da
in
out
When
H`` = - inner
 . H0&=outer
- 4 . shapes
. (D - are
D spherical
) a .  . H0
in
out
D = D
Induced
Field H`` = 0

in
polar axis a
out
 = 4 .  . (D - D
)a . 
For
out a spherical shape D-factor = 0.333
equatorial axis b
m = a/b

in
Induced
Field / 4 .  .  . H0 = 0.333 - Dellipsoid
When inner & outer shapes are spherical
in
out
D = D
polar axis b
Induced Field H`` = 0
polar axis a
equatorial axis a
 = b/a
Thursday, July 28, 2016
MR Symposium 05-02-2003
5
In the above case of two different shapes the example chosen is such that for the entire
specimen the Magnetic moment induced due to the magnetization of the sample is the same in
both cases of the shapes as indicated by the length of the arrow. If this point dipole is at the
center of the specimen in both cases, then the field sistribution around the specimen outside
the specimen would be the same.
Even if the total moment is subdivided into amaller values and paced distributively at different
points, because of the essential spherical symmetry of the first specimen,the calculation may
not indicate much difference in the field patterns outside.
In the case of an elongated ellipsoid a redistribution would require more number of subdivided
dipoles along the length than the width which means a necessary difference in the field
distribution outside the specimen. Hence more than the quantitative aspects the qualitative
patterns for field distributions outside can be indicative of the shape of the specimen.
If one obtains a field pattern for the outside of the specimen by appropriate experiments fitting
the few field values obtained for poits outside the specimen consistently with the values
obtained for tose field values by the present approach (which seems simple enough)then it
may be possible to get informations about the shapes more definitely. By altering the extents
of magnetization by added susceptibility reagents, devicing appropriate experiments and
predetermining favourable values for the experimental parameters would be much more
amenable and tractable for reliable interpretations from the trends.
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MR Symposium 05-02-2003
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Inner ellipsoid
a/b=0.25
demgf= 0.697
Outer ellipsoid
a/b=0.25
demagf= 0.708
Ellipsoid
Outer a/b=0.25
Inner a/b=0.25
demagf=0.333
Outer sphere
Inner sphere
a/b=1
demagf=0.333
From the standard tables demagnetization factor for a/b=0.2: =0.750484
for a/b=0.3: =0.661350
interpolation yields for 0.25: = 0.705
417
It is only conventional in material physics consideration to have a
spherical (Lorentz) cavity while calculating the demagnetization factors
for regular outer shapes of the magnetized specimen. By the procedures
used in this work,it is a matter of simple alteration in sequence in which
certain equations defining the shpes and forms are considered which
makes it possible,without any resulting complications in the calculation,to
get values for Facotrs, based on the definition of demagnetization
factors,as reported above by applying the shapes inside out . This seems
to be very favourable for studying shapes, with added susceptibility
reagents in membrane-media, by spin-echo NMR techniques.The details
are deferred to future presentations.
Thursday, July 28, 2016
MR Symposium 05-02-2003
7
It may be necessary to calculate the intermolecular
contributions inside the Spherical samples with an
elliptical shape of the lorentz sphere and find the
CLICK HERE
For a glimpse of
Crystal systems
as well
The Simpler method (Details to be viewed
(Link
for details / CLICK
option)
optionally
from
other slides)of calculating
Demagnetizing fields makes it possible to
If it is possible to obtain some well defined shape(not necessarily Spherical)
consider
different
combinations
of
specimen of the single crystal samples on which HR PMR studies have well
established
results, then the
experiments
can be made
Macroscopic
sample
Shape
withwith such shapes by
orienting them in 3 independnt rotation axes and try to simulate that shape
hypothetical
Cavity
shapes
to
withappropriate
the same ratios of the
sides
and
faces
but
at
the
range
of
the
Lorentz
Various Specimen
sphere
(about 100 A°
calculate
intermolecular
increase
the) and
utility
oftheHR
PMR lorentz type
shapes
with
the
contributions with the Demagnetizing field type calculation and retrieve the
variety
of Cavity
in
intrameasurements
molecular contribution
as itSolids
was
done with the spherical samples and
conveniences of calculating.
reproduce those values. shapes
Thursday, July 28, 2016
MR Symposium 05-02-2003
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END OF Presentation
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Thursday, July 28, 2016
MR Symposium 05-02-2003
9
Variation of Induced Field at centre of Lorentz' Cavity with centre
position for different cavity sizes
0
-0.5
-1
Induced Field values
-1.5
-2
-2.5
-3
-3.5
-4
-4.5
-5
1.25
1.00
0.75
0.50
0.25
0.00
-0.25 -0.50 -0.75 -1.00 -1.25
Cavity Centre location with respect to the Centre of the Macroscopic Sphere
cav ra1.25
cav ra1.50
cav ra1.75
cav ra2.0
cav ra2.25
Return
display to
slide 4
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MR Symposium 05-02-2003
10
Return
display to
slide 7
Thursday, July 28, 2016
Click to
reach
for the
Web
Site
LINKS
MR Symposium 05-02-2003
11
Link to Internet Web Sites
Link #1 for details of Calculations of Induced Fields and
Demagnetization Factors
Link #2
Link #3
Link #4
http://geocities.com/amudhan20012000/Confview.html
Thursday, July 28, 2016
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Abstract for the MR Symposia 2003, IISc., Bangalore, Feb. 2-6,2003
CAN HR-PMR PROVIDE A FURTHER INSIGHT CONCERNING
THE SPHERICAL SHAPE OF LORENTZ CAVITY?
S.Aravamudhan Department of Chemistry
North Eastern Hill University Shillong 793022 Meghalaya India
a
Email:
[email protected]
Web Site: http://saravamudhan.tripod.com
The Lorentz Cavity, a hypothetical void carved out inside a material medium
while considering the demagnetizing fields at a point (site) inside the materialspecimen, is conveniently described to have a spherical shape since the
demagnetization factor value for spherical external shape is obtained by the
spherical symmetry requirement for such shapes in the homogeneously
magnetized materials. For the case when the external shape is spherical and if,
the carved out cavity also is spherically shaped , then for the inside void one can
have the same numerical value, but negative in sign, as for the spherical outer
shape which encompasses a spherically filled material specimen. This can
result in the required zero Induced fields at the sites inside the material
medium.Then for an ellipsoidal outer shape, it would be possible to get induced
field values by using the demagnetization factor values for ellipsoidal outer
shape and the already eastablished value for the hypothetically carved out
spherical
cavity.
Click for continuation
Thursday,lorentz
July 28, 2016
MR Symposium
05-02-2003 Abstract in the next slide
13
In the previous reports (1) on ‘Calculation of Induced Fields by Simple Summing
Procedures’ and thus, the calculation of Demagnetization Factors, it is mentioned
that the requirement of zero induced field in case of the spherical outer shape for the
specimen has been calculated by this procedure as well. It is being contended here
that the Calculated Induced Field inside a Ellipsoidally shaped specimen can be
equal to zero if the carved out cavity inside the specimen also has the same
ellipsoidal shape since the demagnetization factor for the inner cavity shape and the
outer Specimen shape should be equal in magnitude and opposite sign. HR PMR in
solids, as it would be explained in the presentation, seem to provide a unique context
to acquire a better insight into the necessity for a spherically shaped specimens for
obtaining only the intramolecular symmetry determined shielding tensors. An
inquiry as to ‘what the shape of the Lorentz cavity can also be’ becomes possible by
being sensitive enough for the intermolecular contributions to Shielding tensors
from the neighbouring molecules and groups around a given particular proton site
which can be calculated by the recently reported simple procedure(for even the
hitherto unreported shapes) and, by considering these aspects by the experimental
determination of the proton shielding tensors in single crystals and supplemented
with the necessary calculated (anisotropic) induced fields at the site which should
take the considerations of shape dependences of such fields appropriately.
Ref: (1) Web Site: http://saravamudhan.tripod.com and the HOTLINKS at
and from http://geocities.com/amudhan_nehu/nehu_link.html
Thursday, July 28, 2016
MR Symposium 05-02-2003
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14
Spin Precession Animation
“DEMO”
Precession Starts
Automatically
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slide
Nuclear Spin
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MR Symposium 05-02-2003
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Crystal Systems
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CLICK to Return to slide#8
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