K. Yoshii

Magnetism and transport of Ln0.5Sr0.5CoO3 (Ln = Pr, Nd, Sm and Eu)

Abstract Magnetism and transport have been investigated for perovskite cobalt oxides Ln 0.5 Sr 0.5 CoO 3 ( Ln = Pr, Nd, Sm and Eu). The crystal structures are monoclinic ( P2 1 /n ) for Pr 0.5 Sr 0.5 CoO 3 , orthorhombic ( Pnma ) for Nd 0.5 Sr 0.5 CoO 3 and Sm 0.5 Sr 0.5 CoO 3 , and cubic ( Pm 3 m ) for Eu 0.5 Sr 0.5 CoO 3. DC magnetization measurements showed ferromagnetic transitions with Curie temperatures ( T C ) between 233 and 155 K. Metallic behavior was observed in resistivity-temperature curves below 300 K. This is an entirely different property from that of Ln 0.5 Ba 0.5 CoO 3 , which may be qualitatively explained in connection with the crystal structures.

Structural and magnetic properties of the perovskites Srn+1(Co0.5Nb0.5)nO3n+1 (n=∞, 2 and 1)

The perovskites Srn+1(Co0.5Nb0.5)nO3n+1 (n=∞, 2 and 1) have been prepared. The crystal structures are cubic Pm3m for SrCo0.5Nb0.5O3 (n=∞) and tetragonal I4/mmm for Sr3(Co0.5Nb0.5)2O7 (n=2) and Sr2Co0.5Nb0.5O4 (n=1), respectively, with random occupation of the Co and Nb ions at the same site. DC magnetization–temperature (M–T) curves of SrCo0.5Nb0.5O3 reveal an antiferromagnetism-like transition at 19–20 K. Also the deviation from a Curie–Weiss (CW) law is observed between ∼20 and ∼250 K in inverse magnetization–temperature curves. For Sr3(Co0.5Nb0.5)2O7 and Sr2Co0.5Nb0.5O4, the CW law is well obeyed above ∼100–160 K, and effective Co moments are considerably smaller than that of SrCo0.5Nb0.5O3. They exhibit no obvious magnetic order in their M–T curves, while magnetization–field (M–H) curves show hysteresis loops at 2 K.

Structure, magnetism and transport of La2NiRuO6

Abstract Structure, magnetism and transport properties have been investigated for the perovskite La2NiRuO6. The crystal structure can be refined to monoclinic P21/n where Ru4+ and Ni2+ are settled with ordered arrangement. An electrical resistivity measurement shows that this compound is insulating below room temperature. Magnetization measurements show a magnetic transition at around 20 K. From AC magnetic susceptibility measurements, it is assumed that this transition is brought about by antiferromagnetic order.

Magnetic study of the mixed orthotitanate La1-xSmxTiO3 (0≤x≤1)

Magnetic and structural properties were investigated for the mixed lanthanide solid solution La1−xSmxTiO3 (x=0, 0.0625, 0.125, 0.1875, 0.25, 0.375, 0.5, 0.75 and 1). It was found that all the systems form an orthorhombic perovskite phase (GdFeO3 type) throughout the whole composition range 0≦x≦1. LaTiO3 (x=0) showed so-called canted-antiferromagnetic ordering at TN (Neel temperature) ∼130 K. The ordering temperature of SmTiO3 (x=1) was ∼50 K. The solid solution compounds exhibited magnetic ordering at TN as well, which decreases steadily with x. However, the χ−T (d.c. susceptibility–temperature) curves in some La-rich systems with 0<x<0.3, where crystallographic modification from LaTiO3 is rather minor, were entirely different from those of the end compounds, and represented characteristic susceptibility peaks below TN values. Around the susceptibility peak temperatures (TP values), the most pronounced magnetic hysteresis loops were obtained in the magnetization–field (M–H) isotherm curves. At lower temperatures, magnetization (M) was found to show time (t)-dependent relaxation behavior as observed in spin-glass and/or cluster-glass systems. From the absence of the two characteristic features of spin-glass, i.e., aging effect below Tg (spin-glass transition temperature) and negative divergence of nonlinear AC susceptibilities at Tg, the onset of a cluster-glass state is suggested in these La-rich systems.

Structural and magnetic studies of the lanthanide deficient perovskite Ce2/3TiO3

Abstract The lanthanide deficient perovskite Ce 2/3 TiO 3 was synthesized in vacuum at 1400°C, and the actual formula was found to be Ce 2/3 TiO 2.95 from thermogravimetry. Its crystal structure was refined to the same structure as in La 2/3 TiO 3 , i.e. the orthorhombic double perovskite structure Pmmm having the crystallographic ordering of Ce vacancy along the c -axis. No obvious magnetic ordering was observed between 2 and 300 K in DC susceptibility–temperature ( χ – T ) curves. It was also suggested that the valence of the Ce ions is changed to 3+ (4f 1 ) from the initial valence 4+ (4f 0 ) during the sample firing in vacuum, as is the case for CeTiO 3 and Ce 1− x A x TiO 3 (A=Sr and Ba). Inverse susceptibility–temperature (1/ χ – T ) curves deviated from the Curie–Weiss law below ∼60 K. Magnetization–field ( M – H ) curves exhibited almost only paramagnetic profiles down to 2 K.

Magnetic behavior of CeTi1−xVxO3

The structural and some of the magnetic properties of the perovskite CeTi1−xVxO3 have been investigated for 0≤x≤1. Their crystal structures could be assigned to orthorhombic Pnma as for the end compounds of CeTiO3 (x=0) and CeVO3 (x=1). An almost continuous change of lattice parameters is indicative of a continuous formation of the solid solutions. From magnetization measurements, ordered magnetization and magnetic transition temperatures exhibit minima around x=0.5. AC susceptibility measurements show the presence of a spin-glass or cluster-glass phase in a wide composition region of ∼0.2

Magnetic behaviors of Pr1-xNdxTiO3 (0≤x≤1)

A possible origin of the characteristic susceptibility (magnetization) peaks in the mixed orthotitanate Pr1−xNdxTiO3 (0≤x≤1), which has been found for 0.5<x<1, is proposed based on the results of DC and AC magnetization measurements. Considering the identical results to those in La1−xSmxTiO3 and Ce1−xNdxTiO3, it is assumed that the phenomenon is brought about by the formation of a cluster-glass. In small x regions, the following phenomena are observed. Magnetization–field (M–H) curves show inflection at H<1.2×106 A/m (∼15 000 Oe), plausibly due to a spin-flop of Pr3+ moments. Only at 2 K, the systems exhibit discontinuous jumps of magnetization at some applied fields. From the experiment on a powder sample, this behavior is attributed to rotation of magnetic domains induced by the applied field.