Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical propertie...

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

Influence of cation order-disorder phenomena on the crystal structure, magnetic, and electrical transport properties of new CMR perovskites for LBaMn 2 O 6 - γ (L=Pr, Nd, Sm, Eu, Gd, Tb) series has been investigated. For each rare-earth ion three compounds have been synthesized by the topotactic reduction-oxidation method. Structural investigations have shown the oxygen-stoichiometry LBaMn 2 O 6 compound obtained in air to be cubic with disordered L 3 + and Ba 2 + cations whereas the oxygen-deficient LBaMn 2 O 5 is tetragonal with ordered L 3 + and Ba 2 + and alternate stacking of rare earth and barium containing layers along c. This crystal structure is similar to the YBaCuFeO 5 related one. Another form of oxygen-stoichiometry LBaMn 2 O 6 compound obtained by reoxidation of oxygen-deficient LBaMn 2 O 5 is also tetragonal and retains the ordering of L 3 + and Ba 2 + cations. It is notable that the reoxidized EuBaMn 2 O 6 compound has an orthorhombic unit cell. It is observed that this type of cation ordering leads to considerable increase of transition temperature to paramagnetic state. For example, disordered EuBaMn 2 O 6 compound has magnetic properties similar to spin glass and shows freezing temperature of magnetic moments T f 40 K while ordered EuBaMn 2 O 6 is an inhomogeneous ferromagnet with Curie point T C 260 K. Electrical resistivity behavior correlates with magnetization. Below the T C the Pr, Nd, Sm based compounds undergo a transition to metallic state and demonstrate a peak of magnetoresistance. It is supposed that the remarkable changing of the magnetic and electrical properties of the reoxidized compounds is a consequence of the L/Ba ordering and can be explained on the base of the Goodenough-Kanamori rules for 180° indirect superexchange interactions taking into account an ion size effect in A sublattice of perovskite.

Magnetic and electrical properties ofLBaMn2O6−γ(L=Pr,Nd, Sm, Eu, Gd, Tb) manganites

Nanocrystalline manganite La0.50Ba0.50MnO3 was synthesized by an optimized sol-gel method. The initial sample was subjected to step-by-step heat treatment under air atmosphere. The ion stoichiometry, the morphology of crystallites of ceramics, and the magnetic properties were studied. It is established that the average crystallite size D increases from ∼30 nm to ∼7 μm with increasing annealing temperature. All of the samples studied are characterized by a perovskite-like cubic structure, with the unit cell parameter a increasing continuously from ∼3.787 to ∼3.904 A with the average crystallite size. The most significant lattice compression (≈3%) occurs in the sample with an average crystallite size of ∼30 nm. The increase in the average crystallite size causes a nonmonotonic increase in the Curic temperature T
 C from ∼264 to ∼331 K and in the spontaneous magnetic moment σ
 S
 from ∼1.52 to ∼3.31 μB/f.u. The anomalous behavior of the magnetic properties of the manganite La0.50Ba0.50MnO3 obtained is explained by the competition between two size effects, namely, the frustration of the indirect exchange interactions Mn3+-O-Mn4+ on the nanocrystallite surface and the crystal lattice compression due to the crystallite surface tension.

Effect of the size factor on the magnetic properties of manganite La 0.50 Ba 0.50 MnO 3

The effect of treatment conditions on the magnetic and magnetotransport properties of A-site ordered PrBaMn2O6−δ manganites is examined. The parent oxygen-stoichiometric A-site ordered PrBaMn2O6 samples were prepared from oxygen-stoichiometric A-site disordered Pr0.50Ba0.50MnO3 ones by using a 'two-step' synthesis method. The most significant structural feature of the A-site ordered manganites is that the MnO2 sublattice is sandwiched by two kinds of rock-salt layers, PrOx and BaO. The oxygen-stoichiometric A-site ordered PrBaMn2O6 demonstrates a ferromagnetic metal to paramagnetic insulator transition with the Curie point at about 320 K. These compounds are stable in air up to 1300 °C. The A-site ordered PrBaMn2O6 samples were next reduced in flowing argon as well as being treated under high pressure conditions. The reduction of the A-site ordered PrBaMn2O6 samples leads to the appearance of an antiferromagnetic state with a Neel point of about 140 K, while the A-site order remains. Upon high pressure treatment the degree of A-site order decreases, which reduces TC to 180 K. The magnetotransport properties of A-site ordered manganites treated under different conditions are discussed in terms of the manganese valence, oxygen content and degree of A-site order.

http://iopscience.iop.org/article/10.1088/0953-8984/17/41/019/pdf

Study of A-site ordered PrBaMn2O6−δ manganite properties depending on the treatment conditions

It is shown that oxidized La0.5Sr0.5 (Mn3+0.5Mn4+0.5)O3 and reduced Pr0.5Ba0.5Mn3+O2.75 samples show similar magnetic and magnetoresistive properties. Both compounds, characterized by TCγ 320 K, exhibit a ferromagnetic-antiferromagnetic transition around 200 K, where a large magnetoresistance develops. However, the reduced sample has a much larger resistivity than the oxidized one. These data suggest that some of the intriguing properties of the manganites can also be realized without mixed manganese valences.

Effect of oxygen content on the magnetic and transport properties of Pr0.5Ba0.5MnO3-γ

The influence of oxygen content on the magnetization and electrical resistivity of Ln0.5A0.5MnO3 (Ln=La, Pr, Nd; A=Ca, Ba) manganites with the perovskite structure is investigated. It is shown that the La0.5Ca0.5MnO3−γ compound undergoes a sequence of transitions from an antiferromagnetic (γ=0) to a spin-glass (γ=0.17) state and then to an inhomogeneous ferromagnetic (γ=0.3) state. A transition from an antiferromagnetic charge-ordered state to a ferromagnetic charge-disordered state in Nd0.5Ca0.5MnO3−γ is observed as the oxygen content is reduced to where γ=0.07. The Nd0.5Ba0.5MnO3−γ compound shows an increase of the Curie point from 110 K(γ=0) to 310 K(γ=0.3). In addition, a large magnetoresistance is revealed which develops below their Curie temperature despite the absence of Mn3+−Mn4+ pairs. A Zener double-exchange interaction is usually used in literature to explain the magnetic and electrical properties of hole-doped perovskite manganites. The data obtained support the mechanism of superexchange inte...

/pdf/effect-of-oxygen-content-on-magnetization-and-39new40fhn.pdf

K. Baerner

Papers

Effect of oxygen content on the magnetic and transport properties of Pr0.5Ba0.5MnO3-γ

Effect of oxygen content on magnetization and magnetoresistance properties of CMR manganites