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.

scholarly journals Investigation of Lattice Effects in Rare Earth Manganites by 18O-isotope Exchange

1999 ◽  
Vol 52 (2) ◽  
pp. 235 ◽  
Author(s):  
R. Mahesh ◽  
M. Itoh
Keyword(s):  
Rare Earth ◽  
Colossal Magnetoresistance ◽  
Charge Ordering ◽  
Perovskite Manganites ◽  
Lattice Effects ◽  
Jahn Teller ◽  
18O Isotope ◽  
Ionic Size ◽  
Rare Earth Manganites ◽  
A Site

The strong coupling between the electron spin and lattice arising from the Jahn-Teller effect of manganese ions plays an important role in the mechanism of colossal magnetoresistance and related properties of the rare earth manganites. The lattice effects in this class of oxides have been extensively studied through the application of hydrostatic as well as chemical pressures and magnetic fields. The recently observed giant 18O isotope effect provides direct evidence for the formation of lattice polarons in manganites. Here we report the preliminary results of our investigations on a variety of normal as well as 18O isotope-exchanged perovskite manganites exhibiting colossal magnetoresistance and charge ordering. The observed isotope shift of Tc as well as that of Tco is correlated with the key parameters controlling the lattice such as the Mn 3+ content, the average ionic radius of the A-site cation ⟨rA⟩ , and the A-site ionic size disorder σ2 .

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 From double exchange to superexchange in charge ordering perovskite manganites

1998 ◽  
Author(s):  
W. Bao ◽  
J.D. Axe ◽  
C.H. Chen ◽  
S.W. Cheong ◽  
P. Schiffer ◽  
...  
Keyword(s):  
Double Exchange ◽  
Charge Ordering ◽  
Perovskite Manganites

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.

Electronic Structure and Conductivity Mechanism in Manganite Thin Films Exhibiting Colossal Magnetoresistance

1998 ◽  
Vol 4 (S2) ◽  
pp. 620-621
Author(s):  
Kannan M. Krishnan ◽  
Honglyoul Ju ◽  
C. Nelson
Keyword(s):  
Magnetic Field ◽  
Thin Films ◽  
Electrical Resistance ◽  
Colossal Magnetoresistance ◽  
Magnetic Moments ◽  
Double Exchange ◽  
Perovskite Manganites ◽  
Sensing Applications ◽  
Recent Interest ◽  
Small Change

Perovskite manganites, which have the the general formula R1-xAxMnO3 (R = La, Pr, or Nd and A = Ca, Sr, Ba, or Pb), have generated much recent interest because they exhibit “colossal magnetoresistance” (CMR), i.e. a small change in an applied magnetic field dramatically changes the electrical resistance of the material. Materials that exhibit this effect are being developed for various field-sensing applications but currently, the mechanism by which CMR occurs is not known. Conduction in these materials is explained by the “double exchange” mechanism, where the conductivity is attributed to electrons hopping back and forth between neighboring manganes ions. Such hopping is a maximum when the magnetic moments of the magnese ions are aligned parallel and a minimum when they are aligned antiparallel. In short, these materials show metallic conductivity when they are ferromagnetic and insulating behavior when they are antiferromagnetic. Moreover, they change from metallic to insulating behavior as a function of temperature.

STUDY OF MAGNETIZATION IN MANGANITE SYSTEM IN THE PRESENCE OF LATTICE DISTORTION

2006 ◽  
Vol 20 (15) ◽  
pp. 2093-2116 ◽  
Author(s):  
G. C. ROUT ◽  
N. PARHI ◽  
S. N. BEHERA
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Colossal Magnetoresistance ◽  
Lattice Distortion ◽  
Zeeman Splitting ◽  
Model Parameters ◽  
Coupling Constant ◽  
Magnetic Exchange ◽  
Magnetic Exchange Coupling ◽  
Jahn Teller

The manganites of the type Re1-xAxMnO3( Re = La , Nd , A = Ca , Sr , Ba ) are believed to be half metallic magnets exhibiting colossal magnetoresistance (CMR). The manganite system is described by a simple model Hamiltonian consisting of the hopping of the itinerant d-electrons in the doubly degenerate egband of Mn ions which is split by a static J-T lattice distortion due to band Jahn-Teller (J-T) effect. An external magnetic field results in further Zeeman splitting of the same egband. The ferromagnetism is assumed to originate from the exchange interaction between the spins of the localized core t2gelectrons. The J-T split itinerant (eg) bands are assumed to hybridize rather strongly with the on-site localized (t2g) levels. In the model under consideration the magnetization (m) as well as the lattice strain (e) are expected to depend on the model parameters of the system: i.e. the position of the localized level (d) with respect to the Fermi level, the strength of hybridization (v), the magnetic exchange coupling constant (g1), J-T coupling constant (g), external magnetic field (b) and the impurity concentration (x). The equations for the magnetization and the lattice distortion are solved self-consistently. The effect of different interactions on the quasiparticle bands and the density of states (DOS) are analyzed in detail to understand the evolution of the physical properties of the system on switching the interactions. The temperature dependence of the magnetization due to the localized electrons and that induced in the conduction band are studied.

scholarly journals Effect of the Grain Size on the Magnetic Phase Separation in La0.8Sr0.2MnO3 by Magnetic Force Microscopy

2012 ◽  
Vol 18 (S5) ◽  
pp. 101-102
Author(s):  
P. De Sousa ◽  
N. Panwar ◽  
I. Bdikin ◽  
A. L. Kholkin ◽  
C. M. Fernandes ◽  
...  
Keyword(s):  
Grain Size ◽  
Phase Separation ◽  
Colossal Magnetoresistance ◽  
Room Temperature ◽  
Magnetic Phase ◽  
Magnetic Domain ◽  
Charge Ordering ◽  
Perovskite Manganites ◽  
Fundamental Study ◽  
Metallic Clusters

Perovskite manganites have been the focus of worldwide research during the last two decades because of the observation of colossal magnetoresistance (CMR) effect. These materials have potential applications in magnetic field sensors, spin filters, infrared bolometers and cathodes for solid oxide fuel cells. Such manganites are also important from the fundamental study viewpoint as they offer interplay among various degrees of freedom viz. spin, lattice and charge ordering. Moreover, phase separation may occur in manganites with low concentration of the dopant. In such scenario, ferromagnetic metallic clusters are embedded in antiferromagnetic insulating matrix. The fraction of these magnetic phases may vary from the nano- to micro-scale. With higher dopant concentration, the percolation of these magnetic metallic clusters leads to the apparent CMR effect. In this study we focus our attention to the low doped La0.8Sr0.2MnO3 (LSMO) manganite and investigate the possible magnetic phase separation and effect of variation in grain size on the magnetic domain size. La0.8Sr0.2MnO3 possesses Curie temperature (TC) higher than room temperature, therefore the material is supposed to be in the magnetic state at room temperature.

scholarly journals Impact of Ag-Doped on the Ferromagnetic-Metallic Transition in Pr0.75Na0.25mno3 Manganites

2018 ◽  
Vol 7 (4.30) ◽  
pp. 68
Author(s):  
N Khairulzaman ◽  
N Ibrahim ◽  
S Shamsuddin
Keyword(s):  
Single Phase ◽  
Ac Susceptibility ◽  
Double Exchange ◽  
Xrd Analysis ◽  
Charge Ordering ◽  
X Ray Diffraction ◽  
Sem Images ◽  
X Ray ◽  
Jahn Teller ◽  
Jahn Teller Effect

Monovalent doped Pr0.75Na0.25-yAgyMnO3 (y = 0–0.10) manganite have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) as well as DC electrical resistivity and AC susceptibility measurement to clarify the influence of Ag- doped on charge ordering (CO) state. XRD analysis revealed all samples consists of essentially single phase and crystallized in an orthorhombic structure with space group Pnma. SEM images of Pr0.75Na0.25-yAgyMnO3 compound shows the successful substitution of Ag+ ions with the enhancement of the grains boundaries and sizes as well as the compaction of particles. On the other hand, resistivity and susceptibility measurements showed that the y = 0 sample exhibits insulating behavior and anti-ferromagnetic. Interestingly, the ferromagnetic-metallic transition was observed for y = 0.05 due to the revival of double-exchange (DE) mechanism as a result of weakening the Jahn-Teller effect which caused the CO state to be weakened. However, increasing of Ag-doped up to y = 0.10 induce back its transition into anti-ferromagnetic insulating behavior suggestively due to the weakening of DE mechanism.

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.

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