Επίδραση του μεγέθους και της στοιχειομετρίας των ιόντων στην τροχιακή και μαγνητική τάξη σε ενώσεις τύπου περοβσκίτη του Mn

2021 ◽  
Author(s):  
Κωνσταντίνος Γεωργαλάς
Keyword(s):  
Colossal Magnetoresistance ◽  
Double Exchange ◽  
Jahn Teller

Στους περοβσκίτες του Mn το φαινόμενο της κολοσσιαίας μαγνητοαντίστασης (Colossal Magnetoresistance-CMR), περιλαμβάνει μία πολύπλοκη σύζευξη ανάμεσα στους βαθμούς ελευθερίας φορτίου, τροχιακών και ιδιοστροφορμών των μαγνητικών ιόντων του Mn. Η ισχυρή σύζευξη ηλεκτρονίου-φωνονίου και η συσχέτισή της με τις δυναμικές παραμορφώσεις J-T του πλέγματος θα μπορούσαν να συμβάλλουν στη μικροσκοπική ερμηνεία του φαινομένου της CMR. Οι περοβσκίτες του Mn του τύπου LaMn1-xBxO3 (B: μέταλλο μεταπτώσεως όσο και άλλο μεταλλοειδές στοιχείο) αποτελούν ιδανικά συστήματα για να μελετηθεί η στενή σχέση που διέπει τη συλλογική J-T παραμόρφωση του πλέγματος, τις μαγνητικές αλληλεπιδράσεις διπλής ανταλλαγής (Double Exchange-DE) και υπερανταλλαγής (Superexchange-SE) και τον τροχιακό εκφυλισμό.Στην παρούσα εργασία πραγματοποιείται για πρώτη φορά θερμοδυναμική μελέτη της μετάβασης Jahn-Teller (J-T) (η οποία εξαρτάται από την σύζευξη ηλεκτρονίου-φωνονίου) σε ενώσεις LaMn1-xBxO3 και διερευνάται η φύση των έμμεσων SE ή DE αλληλεπιδράσεων ανάμεσα στα ιόντα Mn3+, Mn4+, Cr3+, Fe3+ και Ga3+. Σκοπός της παρούσας εργασίας είναι να φανερωθεί η ισχυρή συσχέτιση μεταξύ τροχιακής και μαγνητικής τάξης στις ενώσεις LaMn1-xCrxO3, LaMn1-xFexO3, LaMn1-xGaxO3 και LaMn1-xCrxO3+δ, υπό την επίδραση της μεταβολής της μέσης ιοντικής ακτίνας στη θέση Β του πλέγματος, και του παράγοντα μη στοιχειομετρίας του O2, δ.Συμπεραίνεται, ότι σε χαμηλότερες συγκεντρώσεις προσμίξεων, x, αποδυναμώνονται πλήρως οι συσχετίσεις των τοπικών J-T παραμορφώσεων του πλέγματος, ενώ σε υψηλότερες συγκεντρώσεις προσμίξεων, x, πραγματοποιείται η εγκατάσταση των ισότροπων SE-FM Mn3+-Mn3+ αλληλεπιδράσεων και της «Ψευδοκυβικής» φάσης. Η εξασθένιση της συλλογικής παραμόρφωσης J-T φαίνεται να επηρεάζεται εκτός από την και από τη φύση των αλληλεπιδράσεων των ιδιοστροφορμών των Cr3+, Fe3+, Ga3+ με τα Mn3+, ενώ πιθανόν η αλληλεπίδραση Mn3+-Cr3+ δεν είναι DE. Εν γένει αναδεικνύεται η ισχυρή σύζευξη της τροχιακής και μαγνητικής τάξης στις εν λόγω ενώσεις.

Manganites

2021 ◽  
pp. 403-428
Author(s):  
Vladimir Z. Kresin ◽  
Sergei G. Ovchinnikov ◽  
Stuart A. Wolf
Keyword(s):  
Colossal Magnetoresistance ◽  
Mixed Valence ◽  
Fundamental Property ◽  
Microscopic Theory ◽  
Double Exchange ◽  
Metallic State ◽  
Electron Hole ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Mixed Valence Compounds

This chapter focuses on manganites. There is a large similarity between the two families of mixed-valence compounds, the cuprates and the manganites. However, manganites display colossal magnetoresistance. The most fundamental property of manganites is the strong correlation between their transport properties and their magnetic properties. This correlation is caused by the double-exchange mechanism. The Hund interaction and the Jahn–Teller effect are the key ingredients of the microscopic theory. The transition to the ferromagnetic and metallic state is of a percolative nature. The superconducting–antiferromagnetic–superconducting Josephson junction is described. One can observe giant oscillations of the Josephson current as a function of a weak external magnetic field. The main properties, including the electron–hole asymmetry can be described in the framework of a generalised two-band picture. A peculiar isotope effect can be observed.

Lattice Effects in Perovskite and Pyrochlore CMR Materials

1997 ◽  
Vol 475 ◽  
Author(s):  
G.H. Kwei ◽  
D.N. Argyriou ◽  
S.J.L. Billinge ◽  
A.C. Lawson ◽  
J.J. Neumeier ◽  
...  
Keyword(s):  
Colossal Magnetoresistance ◽  
Structural Response ◽  
Double Exchange ◽  
Lanthanum Manganite ◽  
Mixed Valency ◽  
X Ray ◽  
Absorption Studies ◽  
Jahn Teller ◽  
Ideal Stoichiometry ◽  
X Ray Absorption

ABSTRACTColossal magnetoresistance (CMR) in doped lanthanum manganite thin films (Lai.xMx, where M is a divalent ion) has been shown to result in a factor of 106 suppression of the resistance. The driving force for the CMR transition is thought to be the double-exchange (DE) interaction. Many studies of both the crystal structure and the local structure of the Lai.xMxMnO3 (with M = Ca, Sr and Ba, as well as Pb) system have now been carried out. As expected, these systems all show a strong coupling of the lattice to the CMR transition. On the other hand, neutron diffraction data and x-ray absorption studies for the Ti2mn2O7 pyrochlore, which also exhibits CMR, shows no deviations from ideal stoichiometry, mixed valency, or Jahn-Teller distortions of the MnO6 octahedron. We present results of crystallographic and local structural studies of these two important classes of CMR materials. compare the differences in structural response, and discuss the implications of these findings to our understanding of these materials.

SPIN AND ORBITAL PHYSICS IN MANGANITES

2001 ◽  
Vol 15 (19n20) ◽  
pp. 2727-2745 ◽  
Author(s):  
R. Y. GU ◽  
Z. D. WANG
Keyword(s):  
Colossal Magnetoresistance ◽  
Lattice Distortion ◽  
Double Exchange ◽  
Charge Ordering ◽  
Perovskite Manganites ◽  
Electronic Correlation ◽  
Strong Electronic Correlation ◽  
Jahn Teller ◽  
Orbital Physics ◽  
Magnetic Orbital

The spin and orbital physics in perovskite manganites is briefly reviewed. Perovskite manganites are well known as the materials exhibiting colossal magnetoresistance (CMR), whose mechanism is based on the double exchange (DE) interaction, in which the electron hopping is connected with the spin configurations of the manganite ions. Recent intensive studies have shown that this DE framework must be subjected to the strong correlation between orbital degenerate electrons. On one hand, the orbital degeneracy itself leads to an anisotropic DE hopping being different from the conventional DE, which in turn may result in the anisotropy of the magnetic structure, such as the A-type or the C-type antiferromagnetism. On the other hand, the electronic correlation between these degenerate electrons plays an important role in determining the phases of the system. The correlation can come from both the on-site Coulomb interaction and the Jahn–Teller coupling between the lattice distortion and the electrons. The interplay of the DE mechanism and the strong electronic correlation leads to various magnetic, orbital and/or charge ordering as well as the phase separation.

The rich physics of A-site-ordered quadruple perovskite manganites AMn7O12

2021 ◽  
Author(s):  
Alexei A. Belik ◽  
Roger D Johnson ◽  
Dmitry Khalyavin
Keyword(s):  
Perovskite Structure ◽  
Double Exchange ◽  
Perovskite Manganites ◽  
Phonon Coupling ◽  
Electron Phonon Coupling ◽  
Jahn Teller ◽  
The Rich ◽  
A Site ◽  
Small Polarons

Perovskite-structure AMnO3 manganites played an important role in the development of numerous physical concepts such as double exchange, small polarons, electron-phonon coupling, and Jahn−Teller effects, and they host a variety...

scholarly journals Colossal Magnetoresistance Without Mn3+/Mn4+ Double Exchange in the Stoichiometric Pyrochlore Tl2Mn2O7

Science ◽  
1996 ◽  
Vol 273 (5271) ◽  
pp. 81-84 ◽  
Author(s):  
M. A. Subramanian ◽  
B. H. Toby ◽  
A. P. Ramirez ◽  
W. J. Marshall ◽  
A. W. Sleight ◽  
...  
Keyword(s):  
Colossal Magnetoresistance ◽  
Double Exchange

SPIN CORRELATIONS OF THE MAGNETORESISTIVE BILAYER MANGANITE La1.2Sr1.8Mn2O7

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3820-3822
Author(s):  
S. Rosenkranz ◽  
R. Osborn ◽  
J. F. Mitchell ◽  
L. Vasiliu-Doloc ◽  
J. W. Lynn ◽  
...  
Keyword(s):  
Colossal Magnetoresistance ◽  
Double Exchange ◽  
Hole Mobility ◽  
Ferromagnetic Transition ◽  
Double Exchange Interaction ◽  
Metal Insulator ◽  
Spin Correlations ◽  
Paramagnetic Region ◽  
X Ray Scattering ◽  
Good Agreement

We review our recent neutron and X-ray scattering studies of the 40% hole doped bilayer manganite La 1.2 Sr 1.8 Mn 2 O 7, which exhibits colossal magnetoresistance above the ferromagnetic transition at T C~113 K. In the paramagnetic region, static diffuse scattering reveals the existence of correlated charges. However, the good agreement of the in-plane spin correlations with the conventional model for quasi two-dimensional XY magnets indicates that the metal-insulator transition is driven by the growth of magnetic correlations. Across the transition, the competition between antiferromagnetic superexchange and ferromagnetic double exchange, observed as canted correlations between spins in neighboring layers within each bilayer, is strongly reduced, indicating a direct link of the double exchange interaction to the hole mobility.

PHONON-ENHANCED KONDO LATTICE MODEL IN COLOSSAL MAGNETORESISTIVE MANGANITES

2006 ◽  
Vol 20 (01) ◽  
pp. 25-29
Author(s):  
JE HUAN KOO ◽  
GUANGSUP CHO
Keyword(s):  
Lattice Model ◽  
Colossal Magnetoresistance ◽  
Manganese Oxides ◽  
Kondo Lattice ◽  
Colossal Magnetoresistive ◽  
Hole Conduction ◽  
Kondo Lattice Model ◽  
Jahn Teller ◽  
Peierls Transition

We investigate theoretically manganese oxides where the colossal magnetoresistance (CMR) is observed. Recent studies show that, if there are both an electron and a hole in the eg-band of Mn , the Jahn–Teller distortions split the band into a conduction band [Formula: see text] and a localized band [Formula: see text]. We find a Kondo lattice model with hole conduction in manganese oxides when the electron in the localized eg-band [Formula: see text] plays the role of the Kondo impurity. The Curie temperature (Tc) and the resistivity are calculated. We also calculate the antiferromagnetic temperature by a spin-Peierls transition.

scholarly journals Dynamic Jahn-Teller Effect and Colossal Magnetoresistance inLa1−xSrxMnO3

1996 ◽  
Vol 77 (1) ◽  
pp. 175-178 ◽  
Author(s):  
A. J. Millis ◽  
Boris I. Shraiman ◽  
R. Mueller
Keyword(s):  
Colossal Magnetoresistance ◽  
Teller Effect ◽  
Jahn Teller ◽  
Jahn Teller Effect

Structural, Magnetic and Electrical Properties of the Slightly Doped Lanthanum Manganites

2010 ◽  
Vol 168-169 ◽  
pp. 481-484
Author(s):  
A.R. Bulatov ◽  
K.G. Bogdanova ◽  
V.A. Golenischev-Kutuzov ◽  
L.V. Elokhina ◽  
E.A. Neifel’d ◽  
...  
Keyword(s):  
Colossal Magnetoresistance ◽  
Magnetic Measurements ◽  
Structural Phase ◽  
Magnetic Ordering ◽  
Electric Resistance ◽  
Structural Phase Transitions ◽  
Lanthanum Manganites ◽  
Temperature Dependences ◽  
Jahn Teller ◽  
Doped Lanthanum Manganites

The temperature dependences of the transverse and longitudinal hypersound velocities at the frequencies (0.5-0.7) GHz were measured in the La1-xSrx MnO3 (x = 0.125; 0.15; 0.175) compositions. Structural phase transitions the position of which is confirmed by the electric resistance and magnetic measurements data for the same samples are observed. These results were analyzed within the model of the competing Jahn-Teller distortions and magnetic ordering. Anomalies in the behavior of the longitudinal hypersound velocities were related to the local Jahn-Teller distortions the suppression of which upon magnetic ordering is considered as a possible origin of a colossal magnetoresistance.

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