Reentrant transition from an incipient charge-ordered state to a ferromagnetic metallic state in a rare-earth manganate

Arulraj, A.; Biswas, Amlan; Raychaudhuri, A. K.; Rao, C. N. R.; Woodward, P.M.; Vogt, Thomas; Cox, D. E.; Cheetham, Anthony K.

doi:10.1103/physrevb.57.r8115

Cited by 51 publications

(39 citation statements)

References 25 publications

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“…To answer this question, the experimentalists introduced the concept of incipient charge ordered state corresponding to the distortion of long-range CO by microscopic metallic clusters [7]. In fact, the existence of such a state implies a kind of phase separation.…”

Section: +mentioning

confidence: 99%

Phase separation in systems with charge ordering

Kagan

Кugel

Khomskii

2001

J. Exp. Theor. Phys.

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A simple model of charge ordering is considered. It is shown explicitly that at any deviation from half-filling (n = 1/2) the system is unstable with respect to phase separation into charge ordered regions with n = 1/2 and metallic regions with smaller electron or hole density. Possible structure of this phase-separated state (metallic droplets in a charge-ordered matrix) is discussed. The model is extended to account for the strong Hund-rule onsite coupling and the weaker intersite antiferromagnetic exchange. An analysis of this extended model allows us to determine the magnetic structure of the phase-separated state and to reveal the characteristic features of manganites and other substances with charge ordering.

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Section: +mentioning

confidence: 99%

Phase separation in systems with charge ordering

Kagan

Кugel

Khomskii

2001

J. Exp. Theor. Phys.

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“…The CO transition is clearer from the magnetic susceptibility data shown elsewhere [10]. The CO in (NdLa) 0.5 Ca 0.5 MnO 3 is distinct from the CO seen in Nd 0.5 Sr 0.5 MnO 3 [10]. In (NdLa) 0.5 Ca 0.5 MnO 3 it is of incipient type and the CO state becomes unstable below 158 K where a ferromagnetic transition sets in and the resistivity drops sharply.…”

Section: Methodsmentioning

confidence: 82%

“…There is an increase in the activation gap (as estimated from the resistivity) at around 240 K where the sample becomes charge-ordered. The CO transition is clearer from the magnetic susceptibility data shown elsewhere [10]. The CO in (NdLa) 0.5 Ca 0.5 MnO 3 is distinct from the CO seen in Nd 0.5 Sr 0.5 MnO 3 [10].…”

Section: Methodsmentioning

confidence: 84%

“…This is also the reason why the resistivity data show hysteresis between the heating and cooling curves. The collapse of the CO gap in this material at low temperatures is an important observation and it has implications for the physics of the CO process in these materials [10].…”

Section: Resultsmentioning

confidence: 99%

“…The samples were characterized by X-rays, and titration methods were used to fix the exact Mn 4+ concentration. The details of sample preparation and characterization are given elsewhere [9,10]. The electrical resistivity (ρ) was determined for 500 K > T > 4.2 K using the usual four-probe technique.…”

Section: Methodsmentioning

confidence: 99%

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Temperature-dependent vacuum tunneling spectroscopy of rare-earth manganates showing colossal magnetoresistance and charge ordering

Biswas

Raychaudhuri

Arulraj

et al. 1998

Applied Physics A: Materials Science & Processing

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We report here the results of vacuum tunneling spectroscopy of rare-earth manganates which show colossal magnetoresistance (CMR) and charge ordering (CO). Three samples with different hole concentrations and average A site cation radii have been studied. A charge-ordering gap (∆ CO ) opens up in the density of states (DOS) near E F , below the charge-ordering transition. A gap comparable to the transport gap opens up in the paramagnetic state also. There is an absence of gap only in the ferromagnetic metallic state. We have measured the temperature dependence of these quantities.Since the recent discovery of colossal magnetoresistance (CMR) in hole-doped rare-earth manganates, their novel transport properties have been investigated extensively [1,2]. These rare-earth manganates with general formula RE (1−x) A x MnO 3 (RE = La, Nd, Pr, Sm, etc. and A = Ca, Sr, Ba, Pb, etc.) show a fine interplay of magnetic, Coulomb and lattice interactions which manifest themselves through such phenomena as insulator-metal transitions, CMR and charge ordering (CO). Mn ions in these compounds have mixed valency with the Mn 4+ /Mn 3+ ratio ≈ x/(1 − x), depending on the exact value of the oxygen stoichiometry. These oxides belong to the ABO 3 perovskite class of structure where the A site is occupied by the Re or M ions and the B site by the Mn ions. For certain values of x ≈ 0.2-0.3 these materials show CMR close to the ferromagnetic transition temperature, T C , when fields of a few tesla are applied. The stability of the ferromagnetic metallic state depends on the bandwidth W which can be controlled through external pressure [3] or alternatively through the average radius of an A-site cation ( r A ) [4]. As r A becomes smaller the lattice is distorted leading to a smaller transfer matrix and a smaller W. This in turn reduces the T C . When r A is sufficiently small the ferromagnetic T C vanishes, as in solids with RE = Nd, Pr and A = Ca [4]. Lattice effects play an important role in both carrier transport and magnetism in these materials by con- * trolling the bandwidth and the Jahn-Teller (J-T) distortion around the Mn 3+ ions, which results in strong electron-lattice interaction.For materials with smaller A-site cations ( r A ≤ 1.25 Å) near half-filling (x ≈ 1/2), the Coulomb interaction can overcome the kinetic energy of the electrons leading to arrangement of the Mn 3+ and Mn 4+ in alternate lattice sites. This CO transition is associated with large lattice distortions and leads to localization of the carrier and the material becomes insulating below the transition temperature, T CO [5]. For materials like Nd 0.5 Sr 0.5 MnO 3 ( r A ≈ 1.22 Å) the CO transition is associated with the onset of antiferromagnetic ordering i.e. T CO ≈ T N , the Néel temperature [5]. In materials with even smaller r A (≤ 1.18 Å) the CO transition is more gradual and the AFM ordering may take place at a lower temperature [6,7]. Lattice distortion (through the J-T effect) plays an important role in ushering in the CO insulating state. The orthorhombic...

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Colossal Magnetoresistance and Charge‐ordering in Rare Earth Manganites

Raveau

Rao

2001

Magnetism: Molecules to Materials I

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Reentrant transition from an incipient charge-ordered state to a ferromagnetic metallic state in a rare-earth manganate

Cited by 51 publications

References 25 publications

Phase separation in systems with charge ordering

Phase separation in systems with charge ordering

Temperature-dependent vacuum tunneling spectroscopy of rare-earth manganates showing colossal magnetoresistance and charge ordering

Colossal Magnetoresistance and Charge‐ordering in Rare Earth Manganites

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