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.

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 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

Dynamic Jahn–Teller effect for an electronic E state coupled to the phonon continuum. II

1976 ◽  
Vol 54 (1) ◽  
pp. 9-25 ◽  
Author(s):  
Napoléon Gauthier ◽  
M. B. Walker
Keyword(s):  
Degrees Of Freedom ◽  
Phonon Scattering ◽  
Resonance Spectrum ◽  
Effective Hamiltonian ◽  
Spin Resonance ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Lattice Coupling ◽  
Motional Narrowing ◽  
Reduced Density

A coherent formalism describing the electron spin resonance of Jahn–Teller ions in 2E states in cubic crystals (the coupling being to the phonon continuum) is developed using thermal Green function techniques. The basic equation of the theory is a Wangsness–Bloch–Redfield equation of motion for the reduced density matrix for the combined spin and orbital degrees of freedom of the Jahn–Teller ion. The effective Hamiltonian and the t matrices describing phonon scattering processes are calculated by perturbation theory and several results for these quantities are given for both linear and quadratic orbit–lattice coupling. The effect of motional narrowing on the observed resonance spectrum of the 2E state is studied and results in agreement with experimental observations are found.

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 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.

scholarly journals ORBITAL EFFECTS IN MANGANITES

2001 ◽  
Vol 15 (19n20) ◽  
pp. 2665-2681 ◽  
Author(s):  
D. I. KHOMSKII
Keyword(s):  
Phase Diagram ◽  
Colossal Magnetoresistance ◽  
Degrees Of Freedom ◽  
Short Review ◽  
Orbital Ordering ◽  
Orbital Degeneracy ◽  
Structural Distortions ◽  
Jahn Teller ◽  
Different Parts

In this paper I give a short review of some properties of the colossal magnetoresistance manganites, connected with the orbital degrees of freedom. Ions Mn 3+, present in most of these compounds, have double orbital degeneracy and are strong Jahn–Teller ions, causing structural distortions and orbital ordering. Mechanisms leading to such ordering are shortly discussed, and the role of orbital degrees of freedom in different parts of the phase diagram of manganites is described. Special attention is paid to the properties of low-doped systems (doping 0.1≤x≤0.25), to overdoped systems (x>0.5), and to the possibility of a novel type of orbital ordering in optimally doped ferromagnetic metallic manganites.

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