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.

scholarly journals Ca3Ru2O7: A NEW PARADIGM FOR SPINTRONICS

2008 ◽  
Vol 22 (19) ◽  
pp. 1785-1813 ◽  
Author(s):  
G. CAO ◽  
P. SCHLOTTMANN
Keyword(s):  
Colossal Magnetoresistance ◽  
Degrees Of Freedom ◽  
Spin Valve ◽  
Metallic State ◽  
The Novel ◽  
New Paradigm ◽  
Quantum Oscillations ◽  
Jahn Teller ◽  
Bulk Single Crystals ◽  
Jahn Teller Effect

Ca3Ru2O7, the bilayered member of the Ruddlesden–Popper (RP) series of Ca -ruthenates, displays a vast variety of physical properties that not only span almost every ordered state (except for superconductivity) known in condensed matter physics, but includes exotic phenomena not found in other materials. In this review article, we first present a brief introduction of the layered ruthenates and then discuss transport and thermodynamic properties of Ca3Ru2O7with a focus on the following intriguing issues: (i) Colossal magnetoresistance (CMR) via suppression of a ferromagnetic (FM) state, (ii) Strong spin valve effect in bulk single crystals, (iii) Quantum oscillations in the non-metallic state, and (iv) Oscillatory magnetoresistance periodic in B (rather than 1/B). It has become increasingly clear that the orbital degrees of freedom of the Ru -ions drive the complex phase diagram via couplings of these orbital degrees of freedom to the spin (spin-orbit interaction) and the lattice (Jahn–Teller effect). The novel and surprising properties of the ruthenates is ultimately defined by these couplings.

The crucial role of mixed valence in the magnetoresistance properties of manganites and cobaltites

2007 ◽  
Vol 366 (1862) ◽  
pp. 83-92 ◽  
Author(s):  
B Raveau
Keyword(s):  
Colossal Magnetoresistance ◽  
Mixed Valence ◽  
Transition Element ◽  
Oxygen Stoichiometry ◽  
Orbital Ordering ◽  
Electronic Phase ◽  
Spin Glass Behaviour ◽  
Jahn Teller ◽  
Jahn Teller Effect

The mixed valence Mn 3+ /Mn 4+ and Co 3+ /Co 4+ in manganites and cobaltites with the perovskite structure is absolutely necessary for the appearance of magnetotransport properties. It is shown that in these systems the Jahn Teller effect of the transition element, the charge and orbital ordering and the oxygen stoichiometry play a key role in the appearance of large and even colossal magnetoresistance. It has been discovered that these oxides exhibit a new phenomenon, the crystallographic and electronic phase separation. It is this phenomenon that is at the origin of the competition between ferromagnetism and antiferromagnetism or spin glass behaviour and which leads to the negative magnetoresistance (MR). The doping of these materials at different sites appears then to be a means of inducing large MR effects.

scholarly journals Quantum Chemistry in Moldova – 50 Years

2009 ◽  
Vol 4 (1) ◽  
pp. 36-43
Author(s):  
B. Bersuker
Keyword(s):  
Quantum Chemistry ◽  
Chemical Activation ◽  
Structural Phase ◽  
Mixed Valence ◽  
Molecular Systems ◽  
General Law ◽  
Effect Theory ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Mixed Valence Compounds

An overview of the main achievements of the Laboratory of Quantum Chemistry of the Institute of Chemistry of the Academy of Sciences of Moldova during the 50 year of its existence is briefly outlined. The main fundamental non-transient result obtained in this laboratory is the generalization of the Jahn-Teller effect theory formulated and proved as a general law of instability of polyatomic systems and its application to a variety of physical, chemical, and biological problems, including al-range spectroscopy, geometry and spectra of molecular systems, structural phase transitions, ferroelectricity, stereochemistry and crystal chemistry, chemical activation and reactivity, electron transfer in mixed-valence compounds, and electron-conformational transitions in biological systems.

scholarly journals Magnetoelectricity in Jahn–Teller Elastics

2021 ◽  
Vol 7 (7) ◽  
pp. 95
Author(s):  
Michael Kaplan
Keyword(s):  
Microscopic Theory ◽  
Teller Effect ◽  
Magnetoelectric Effects ◽  
Jahn Teller ◽  
Jahn Teller Effect

The magnetoelectric effects in Jahn–Teller crystals are discussed on the basis of phenomenology and microscopic theory. New magnetoelectric effects—metamagnetoelectricity—are analyzed. Formation of multiferroic crystal states as the consequence of the cooperative Jahn–Teller effect is discussed.

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

Structure, magnetic and electrical properties of Ln2/3Pb1/3MnO3 (Ln = La, Pr, Nd) films

2008 ◽  
Vol 86 (6) ◽  
pp. 829-833
Author(s):  
L A Han ◽  
C L Chen
Keyword(s):  
Electrical Properties ◽  
Double Exchange ◽  
Orthorhombic Phase ◽  
Rf Magnetron Sputtering ◽  
Metallic State ◽  
X Ray Diffraction ◽  
X Ray ◽  
Jahn Teller ◽  
Higher Temperature ◽  
Ion Radius

Ln2/3Pb1/3MnO3 (Ln = La, Pr, Nd) films deposited on single crystal LaAlO3 substrate were fabricated using the RF magnetron sputtering method. The X-ray diffraction results of bulk targets indicate that with the decrease of the average ion radius < rA >, the structure transits from the rhombohedral to the orthorhombic phase. The magnetic properties show that there is a transition from the ferromagnetic to the paramagnetic state with the increase in temperature, the Curie temperature reduces abruptly with the decrease of < rA >. The electrical properties show that films are in the metallic state, which can be fitted to the formula: ρ(T) = ρ0 + ρ1T2 + ρ2T4.5 at low temperatures and the insulator state, which can be fitted to the formula: ρ(T) = ρ0T exp(Ea/KBT) at higher temperature(T > TMI). The temperature range of the ferromagnetic metallic state becomes narrow with the decrease of < rA >. The phenomenon can be qualitatively and reasonably explained by the double-exchange model and Jahn–Teller effects. PACS Nos.: 75.47.Lx, 74.25.Ha, 75.47.–m, 75.30.Et

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.

scholarly journals Optimized unconventional superconductivity in a molecular Jahn-Teller metal

2015 ◽  
Vol 1 (3) ◽  
pp. e1500059 ◽  
Author(s):  
Ruth H. Zadik ◽  
Yasuhiro Takabayashi ◽  
Gyöngyi Klupp ◽  
Ross H. Colman ◽  
Alexey Y. Ganin ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Metallic State ◽  
Molecular Electronic ◽  
Structure Control ◽  
Unconventional Superconductors ◽  
Itinerant Electrons ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Molecular Electronic Structure ◽  
The Relationship

Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above Tc is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C603– electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller–active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of Tc with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

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