# Changeset 3611 for Tutorials/SimpleMagnetic

Ignore:
Timestamp:
Sep 19, 2018 12:45:33 PM (3 years ago)
Message:

new tutorial - Magnetic-I & some fixes to Simple Magnetic

Location:
Tutorials/SimpleMagnetic
Files:
6 edited

Unmodified
Removed
• ## Tutorials/SimpleMagnetic/SimpleMagnetic.htm

 r3604 Von Dreelevondreele2062242362942017-08-09T17:16:00Z2018-09-16T00:43:00Z15837332742018-09-19T17:37:00Z49589333592Argonne National Laboratory27727978390333940716.00

<<<<<<< .mine

To have this result, one assumes that the neutron beam is not polarized, the sample has no texture and there is only elastic scattering. intensities are summed to give the total that is measured in a magnetic powder diffraction experiment. This allows us to model the structure as two separate crystalline phases; one consists of the chemical arrangement of all the atoms in the crystal structure described with a conventional unit cell and space group, and the other contains only the magnetic atoms in a perhaps different unit cell with a magnetic space group to describe the atom and magnetic moment ||||||| .r3550

To have this result, one assumes that the neutron beam is not polarized, the sample has no texture and there is only elastic scattering. The first term is the ordinary nuclear structure factor found for all crystalline materials and the second is the magnetic scattering. Note that the result is a sum of squares implying that the nuclear and magnetic scattering intensities are summed to give the total that is measured in a magnetic powder diffraction experiment. This allows us to model the structure as two separate crystalline phases; one consists of the chemical arrangement of all the atoms in the crystal structure described with a conventional unit cell and space group, and the other contains only the magnetic atoms in a perhaps different unit cell with a magnetic space group to describe the atom and magnetic moment =======

To have this result, one assumes that the neutron beam is not polarized, the sample has no texture and there is only elastic scattering. The first term is the ordinary nuclear structure factor found for all crystalline materials and the second is the magnetic scattering. Note that the result is a sum of squares implying that the nuclear and magnetic scattering intensities are summed to give the total that is measured in a magnetic powder diffraction experiment. This allows us to model the structure as two separate crystalline phases; one consists of the arrangement of all the atoms in the crystal structure described with a conventional unit cell and space group (the chemical or sometimes "nuclear" structure), and the other contains only the magnetic atoms in a perhaps different unit cell with a magnetic space group to describe the atom and magnetic moment >>>>>>> .r3603 arrangement (the magnetic structure). Needless to say the magnetic ions only have one set of positions, both phases must describe the same atomic arrangement;  positions of the magnetic ions will be linked, as needed, by constraints between the phases in order to maintain this arrangement.

crystalline phases; one consists of the arrangement of all the atoms in the crystal structure described with a conventional unit cell and space group (the chemical or sometimes "nuclear" structure), and the other contains only the magnetic atoms in a perhaps different unit cell with a magnetic space group to describe the atom and magnetic moment arrangement (the magnetic structure). Needless to say the magnetic ions only have one set of positions, both phases must describe the same atomic arrangement; positions of the magnetic ions will be linked, as needed, by constraints between the phases in order to maintain this arrangement.

The magnetic scattering component has two factors

height:48pt;visibility:visible;mso-wrap-style:square'>

minor-latin;mso-hansi-theme-font:minor-latin'>/data/... entry will bring you to the location where the files have been downloaded. (It is also possible to download them manually from https://subversion.xray.aps.anl.gov/pyGSAS/Tutorials/SimpleMagnetic/data/. In this case you will need to navigate to the download location manually.)
src="SimpleMagnetic_files/image003.png" v:shapes="Picture_x0020_3">

and the plot window will show the

src="SimpleMagnetic_files/image004.png" v:shapes="Picture_x0020_4">

Step 2: Select Limits

be careful in selecting the lower limit especially for magnetic structure studies as a small peak may be hidden at low angles that can decisively determine a magnetic structure (there are none in this example, but this issue will be apparent in the next example). Click on the Limits

src="SimpleMagnetic_files/image006.png" v:shapes="Picture_x0020_5">

Step 3: Read in the chemical structure for LaMnO3

mso-ascii-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;mso-bidi-theme-font: minor-latin'>Import/Phase/from CIF file menu item to read the phase information for LaMnO3 into the current GSAS-II project. This read option is set to read Crystallographic Information Files (CIF). Other submenu items will read phase information in other formats.  Because you used the Because you used the This can be use lattice parameters & space groups to generate expected reflection positions to check against the peaks in the powder pattern.

auto'>This can be use lattice parameters & space groups to generate expected reflection positions to check against the peaks in the powder pattern.

This is the reflection set for the Bravais <<<<<<< .mine lattice Pmmm which includes reflections that may be space group extinct and/or magnetically extinct. NB: a reflection that is space group extinct could still be allowed for magnetic scattering.

||||||| .r3550 lattice Pmmm which includes relections that may be space group extinct and/or magnetically extinct. BN: a reflection that is space group extinct could still be allowed for magnetic scattering.

======= auto'>This is the reflection set for the Bravais lattice Pmmm which includes relections that may be space group extinct and/or magnetically extinct. N.B., a reflection that is extinct due to the chemical structure space group could still be allowed for magnetic scattering.

>>>>>>> .r3603 that is extinct due to the chemical structure space group could still be allowed for magnetic scattering.

src="SimpleMagnetic_files/image019.png" v:shapes="Picture_x0020_12">
Notice that the 1st peak (as well as the contaminant) is no longer indexed; this is likely to be a magnetic only peak as expected from an

src="SimpleMagnetic_files/image021.png" v:shapes="Picture_x0020_13">

src="SimpleMagnetic_files/image025.png" v:shapes="Picture_x0020_15">

It

Step 5. Make the magnetic phase

In the previous step we did not have to resort to any doubling of a cell axis to explain the suite of magnetic reflections, so the propagation vector is zero (in case anyone asks!). To make the magnetic cell from the chemical cell we will use the transform tool that is in GSAS-II in the General tab for the chemical structure. That tab is

In the previous step we did not have to resort to any doubling of a cell axis to explain the suite of magnetic reflections, so the propagation vector is zero (in case anyone asks!). To make the magnetic cell from the chemical cell we will use the transform tool that is in GSAS-II in the General tab for the chemical structure. That tab is

src="SimpleMagnetic_files/image027.png" v:shapes="Picture_x0020_16">

Under the

src="SimpleMagnetic_files/image029.png" v:shapes="_x0000_i1080">

The phase is named with mag appended to the end, the phase

src="SimpleMagnetic_files/image031.png" v:shapes="_x0000_i1079">

This shows all the possible required constraints between the

src="SimpleMagnetic_files/image032.png" v:shapes="Picture_x0020_22">

This gives the constraints between the two phases for scale

src="SimpleMagnetic_files/image033.png" v:shapes="Picture_x0020_23">

The boxes that carry the magnetic moment components (

src="SimpleMagnetic_files/image036.png" v:shapes="Picture_x0020_24">

It now shows the magnetic space group as Pnma.

src="SimpleMagnetic_files/image038.png" v:shapes="Picture_x0020_25">

with 0.0 in each of the magnetic

src="SimpleMagnetic_files/image040.png" v:shapes="Picture_x0020_26">

Under the

src="SimpleMagnetic_files/image042.png" v:shapes="Picture_x0020_34">

Scroll down to the bottom and select

src="SimpleMagnetic_files/image046.png" v:shapes="Picture_x0020_37">

The least squares will not begin a refinement of

src="SimpleMagnetic_files/image048.png" v:shapes="Picture_x0020_30">

There does not appear to be any calculated magnetic

src="SimpleMagnetic_files/image050.png" v:shapes="Picture_x0020_31">

The magnetic moment is clearly too small; to let the least

src="SimpleMagnetic_files/image052.png" v:shapes="Picture_x0020_32">

This appears to be a reasonable solution; a more complete

src="SimpleMagnetic_files/image054.png" v:shapes="Picture_x0020_33">

Now set the spin operators to all 

You can see in particular at the pair of peaks at 33.3 and

src="SimpleMagnetic_files/image064.png" v:shapes="Picture_x0020_38">

Looking at the plot, it would seem that the lattice

src="SimpleMagnetic_files/image066.png" v:shapes="Picture_x0020_39">

Since the scan covers a very wide range in 2

src="SimpleMagnetic_files/image068.png" v:shapes="Picture_x0020_40">

Now we can add refinement of the atom positions and thermal style='mso-bidi-font-weight:normal'>La Mn O3

Phase, double click the refine column heading and select X & U. This will add these parameters as allowed by symmetry to the refinement. Now go to the Atoms tab for La Mn O3 mag and double click the refine tab. Select U & M; the Uiso for the Mn atom is tied via a constraint to the Mn in the other phase. Now select Background from the La Mn O3 phase, double click the refine column heading and select X & U. This will add these parameters as allowed by symmetry to the refinement. Now go to the Atoms tab for La Mn O3 mag and double click the refine tab. Select U & M; the Uiso for the Mn atom is tied via a constraint to the Mn in the other phase. Now select Background from the PWDR entry and increase the number of terms to

This curve shows a couple of peaks which are from some contaminating phase, but otherwise the fluctuations are mostly within 2

This curve shows a couple of peaks which are from some contaminating phase, but otherwise the fluctuations are mostly within 2s of zero. Finally examine the magnetic moment components of the Mn atom;

src="SimpleMagnetic_files/image073.png" v:shapes="Picture_x0020_42">

src="SimpleMagnetic_files/image074.png" v:shapes="Picture_x0020_44">

The plot will show the unit cell contents of

src="SimpleMagnetic_files/image075.png" v:shapes="Picture_x0020_45">

This completes this tutorial; you can save the project if

src="SimpleMagnetic_files/image076.png" v:shapes="Picture_x0020_27">

and the

src="SimpleMagnetic_files/image077.png" v:shapes="Picture_x0020_28">

Step 2: Select Limits

src="SimpleMagnetic_files/image079.png" v:shapes="Picture_x0020_29">

Step 3: Read in the chemical structure for

src="SimpleMagnetic_files/image094.png" v:shapes="Picture_x0020_46">

Select the histogram (or press

src="SimpleMagnetic_files/image096.png" v:shapes="Picture_x0020_47">

Notice that the space group from

src="SimpleMagnetic_files/image112.png" v:shapes="Picture_x0020_48">

This

to see details of the indexing

Note

Then check the box Because

In the previous step we did not have to resort to any doubling of a cell axis to explain the suite of magnetic reflections, so the propagation vector is zero (in case anyone asks!). To make the magnetic cell from the chemical cell we will use the transform tool that is in GSAS-II in the General tab for the chemical structure. That tab is

doubling of a cell axis to explain the suite of magnetic reflections, so the propagation vector is zero (in case anyone asks!). To make the magnetic cell from the chemical cell we will use the transform tool that is in GSAS-II in the General tab for the chemical structure. That tab is

src="SimpleMagnetic_files/image130.png" v:shapes="Picture_x0020_53">

Under the

This allows one to select possible magnetic lattice centering operations as given by the BNS nomenclature. This can be needed if one had discovered a requirement of doubling a cell axis in the previous step (e.g. a nonzero propagation vector). This is not required in this case and we are using the same nonstandard space group (Pnma) for the magnetic cell that is used for the chemical cell. Leave the box at the bottom about constraints checked as we want them to tie the two phases together.  Press Ok

This allows one to select possible magnetic lattice centering operations as given by the BNS nomenclature. This can be needed if one had discovered a requirement of doubling a cell axis in the previous step (e.g. a nonzero propagation vector). This is not required in this case and we are using the same nonstandard space group (Pnma) for the magnetic cell that is used for the chemical cell. Leave the box at the bottom about constraints checked as we want them to tie the two phases together.  Press Ok to continue; a new popup will appear

src="SimpleMagnetic_files/image140.png" v:shapes="Picture_x0020_56">

This allows one to reject certain atoms that are known to

src="SimpleMagnetic_files/image141.png" v:shapes="Picture_x0020_57">

The phase is named with mag appended to the end, the phase

src="SimpleMagnetic_files/image142.png" v:shapes="Picture_x0020_58">

Notice

src="SimpleMagnetic_files/image144.png" v:shapes="Picture_x0020_60">

The

src="SimpleMagnetic_files/image146.png" v:shapes="Picture_x0020_61">

If

src="SimpleMagnetic_files/image148.png" v:shapes="Picture_x0020_64">

Clearly

src="SimpleMagnetic_files/image150.png" v:shapes="Picture_x0020_63">

Then do

and the magnetic moment components

So we test the next possibility.

The

src="SimpleMagnetic_files/image155.png" v:shapes="Picture_x0020_68">

Lets test the next one.

src="SimpleMagnetic_files/image156.png" v:shapes="Picture_x0020_69">

The

src="SimpleMagnetic_files/image158.png" v:shapes="Picture_x0020_70">

We should now check the last spin configuration.

src="SimpleMagnetic_files/image160.png" v:shapes="Picture_x0020_71">

and with the strong

src="SimpleMagnetic_files/image175.png" v:shapes="Picture_x0020_72">

src="SimpleMagnetic_files/image194.png" v:shapes="Picture_x0020_74">

The magnetic peaks contributing to this peak are the 200,221

src="SimpleMagnetic_files/image195.png" v:shapes="Picture_x0020_75">

which shows that the ferromagnetic

• ## Tutorials/SimpleMagnetic/SimpleMagnetic_files/filelist.xml

 r3604
Note: See TracChangeset for help on using the changeset viewer.