ELFT HÍRADÓ

[bordacs.sandor AT wigner.bme.hu]

Kedves Kollégák!

Szeretettel várunk benneteket az MTA-BME Lendület Magneto-optikai 
Spektroszkópia Kutatócsoport következő szemináriumára MÁJUS 11-ÉN 10 
ÓRÁTÓL, melynek helyszíne BME F ÉPÜLET I. LÉPCSŐHÁZ 1. EMELET 
SCHAY-TEREM.

PROF. JOCHEN LITTERST
Institut für Physik der Kondensierten Materie, Technische Universitat 
Braunschweig

EXAMPLES FOR COMPLEX MAGNETISM IN SPINELS STUDIED BY MÖSSBAUER 
SPECTROSCOPY AND MUON SPIN ROTATION Μ+SR

Recent µ+SR studies of Fe1-xCuxCr2S4(0 ≤ x ≤ 1) have shown that 
magnetism in this series is far more complex than the earlier assumed 
ferrimagnetism with antiparallel Fe and Cr spins. Also in undoped 
FeCr2S4, several ordered phases are present with an incommensurate cone- 
like helical structure as suspected ground
state. We have performed systematic Mössbauer and µ+SR studies of 
Fe1-xCuxCr2S4(x = 0 to 0.9). The data are discussed together with 
magnetization, electrictransport and caloric data from the same 
preparation. Mössbauer data show that the charge state of the A-site 
iron changes from ferrous for x=0 to ferrous, ferric and intermediate 
valence species for x ≥ 0.1. The magnetic sites due to different 
neighborhoods upon doping can systematically be traced below 
Tc.Jahn-Teller (JT) distortions for the tetrahedrally coordinated 
ferrous iron are observed. From µ+SR the distribution of local fields 
has been analyzed. The data indicate different spin structures below Tc 
what is compatible with the conclusions drawn from Mössbauer data. 
Significant change sin
longitudinal and transverse relaxation rates with temperature have been 
found which are related to spin reorientation transitions and onset of 
JTeffect.
In addition, a brief report will begiven on preliminary µ+SR results on 
the lacunar thiospinel GaV4S8revealing unusual temperature dependencies 
and distributions of local magnetic fields at the interstitial site 
occupied by µ+.


Minden jót, Kézsmárki István

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Dr. Istvan Kezsmarki
Budapest University of Technology and Economics
Department of Physics, associate prof.
MTA-BME Lendulet Magneto-optical Spectroscopy Research Group
http://magnetooptics.phy.bme.hu [1]
Tel: 36-1-4633056
Fax: 36-1-4634180
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