Physik-Praktikum für Vorgerückte:

"Nachweis antiferromagnetischer Fernordnung mittels Neutronendiffraktion"

"Determination of long range antiferromagnetic order by powder neutron diffraction"

Antiferromagnetic (AFM) ordering of Mn spins in manganese sulfide MnS or manganese oxide MnO will be determined by powder neutron diffraction. These compounds crystallize in a rock salt face centered cubic crystal structure. Manganese sulfide MnS shows a transition to the AFM state with the propagation vector k=[1/2 1/2 1/2] at Neel temperature about 150K. The Mn-spins forming planes perpendicular to the body diagonal are ferromagnetically aligned, whereas the spins in the neighboring planes are antiparallel.

During the practicum we will try to reproduce the one of the neutron diffraction experiments performed during 1946-1951 for which C.G. Shull was honored with the Nobel Prize in 1994. We will perform neutron diffraction experiment with MnS using powder diffractometer HRPT/SINQ. From the analysis of the nuclear and magnetic Bragg peak intensities and positions we will verify the crystal and magnetic structures of manganese sulfide and determine the size of the magnetic moment on manganese.

Note: The practicum is performed during only one day at PSI. To perform the experiment effectively and analyze the experimental data it is necessary to have basic theoretical background on mathematical description of crystal structure and diffraction (reciprocal space, Brillouin zone, structure factor, etc.)

Some relevant lectures (by V. Pomjakushin).

"Magnetic order from neutron diffraction experiments: applications of representation decomposition and Shubnikov symmetry", and "Diffraction at swiss spallation source SINQ"
IUCr Congress Satellite Workshop on the Role of Magnetic Symmetry in the Description & Determination of Magnetic Structures, 14-16 August, 2014, Brockhouse Institute for Materials Research, McMaster University, Hamilton, Canada (near Toronto)

"Multi-k magnetic order in Ca3Cu1Ni2(PO4)4: representation approach and Shubnikov symmetry", and Invited talk at IUCr congress August 5-12, 2014, Montreal, Quebec, Canada

"Symmetry constraints in solving magnetic structures by neutron diffraction: Representation analysis and Shubnikov groups", and "Introduction to experimental neutron diffraction" (41 Mb).
Lectures given at the MOTT PHYSICS BEYOND THE HEISENBERG MODEL Master Class, October 26th to 27th, 2013, Paul Scherrer Institut, Villigen, Switzerland".

V. Pomjakushin,"Advanced magnetic structures: classification and determination by neutron diffraction" (Exercize) Lecture given 24.03.2010 at the ETHZ lecture course "Neutron Scattering in Condensed Matter Physics" of Prof. A.Zheludev.

"High Resolution Powder Diffractometer for Thermal Neutrons." (31 Mb).
Talk given at the AIC Information Day on "Large Facilities for Crystallography Studies: Synchrotron and Neutron sources" October 19th, 2009 , Paul Scherrer Institut, Villigen, Switzerland.

"Determination of the magnetic structure from powder neutron diffraction." (11 Mb)
Lecture given at the "Workshop on X-rays, Synchrotron Radiation and Neutron Diffraction Techniques June 18-22, 2008, Paul Scherrer Institut, Villigen, Switzerland".
compacted slides (pdf 9Mb), or