A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained.

Giant magnetocaloric effect of MnAs1−xSbx

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A Toll-like receptor recognizes bacterial DNA

An interpretation of the magnetic properties of the perovskite-type mixed crystals La1-xSrxCoO3-λ

Catalytic converters are widely used to reduce the amounts of nitrogen oxides, carbon monoxide and unburned hydrocarbons in automotive emissions. The catalysts are finely divided precious-metal particles dispersed on a solid support. During vehicle use, the converter is exposed to heat, which causes the metal particles to agglomerate and grow, and their overall surface area to decrease. As a result, catalyst activity deteriorates. The problem has been exacerbated in recent years by the trend to install catalytic converters closer to the engine, which ensures immediate activation of the catalyst on engine start-up, but also places demanding requirements on the catalyst's heat resistance. Conventional catalyst systems thus incorporate a sufficient excess of precious metal to guarantee continuous catalytic activity for vehicle use over 50,000 miles (80,000 km). Here we use X-ray diffraction and absorption to show that LaFe0.57Co0.38Pd0.05O3, one of the perovskite-based catalysts investigated1,2,3,4 for catalytic converter applications since the early 1970s, retains its high metal dispersion owing to structural responses to the fluctuations in exhaust-gas composition that occur in state-of-the-art petrol engines5. We find that as the catalyst is cycled between oxidative and reductive atmospheres typically encountered in exhaust gas, palladium (Pd) reversibly moves into and out of the perovskite lattice. This movement appears to suppress the growth of metallic Pd particles, and hence explains the retention of high catalyst activity during long-term use and ageing.

Self-regeneration of a Pd-perovskite catalyst for automotive emissions control

A2B′B″O6 perovskites: A review

A neutron diffraction study was carried out on SrFeO 3 . The results indicate that the magnetic structure is a helical one with the helicoid vector k ; k // and | k |=0.112 a * . The Fe 4+ magnetic moment is 2.7±0.4 µ B at liquid nitrogen temperature.

Magnetic Structure of SrFeO3

SrCoO 2.5 with brownmillerite (4CaO·Fe 2 O 3 ·Al 2 O 3 ) type structure is an antiferromagnet with the Neel temperature of 570 K. The magnetic structure as determined from a neutron diffraction study is of G-type and the Co 3+ magnetic moment is 3.3±0.5µ B at liquid nitrogen temperature.

Magnetic Structure of SrCoO 2.5

Samples of the system SrCo 1- x Fe x O 3- y (0≤ x ≤1, 0≤ y ≤0.5) have been prepared under varying oxygen pressure and temperature and their crystal-lographic and magnetic properties have been studied. SrCoO 2.5 with brown-millerite type structure (high temperature phase) is an antiferromagnet with the Neel temperature of 570 K and the Co 3+ -O 2- -Co 3+ superexchange interaction is strongly antiferromagnetic. SrCoO 3 and SrCo 1- x Fe x O 3 ( x <0.9) with the cubic perovskite structure (high temperature phase) are ferromagnetic with the Curie temperature at about 200 K and the magnetization decreases rapidly with increasing x near SrFeO 3 whose magnetic structure is helical.

Magnetic Properties of the System SrCo 1− x Fe x O 3− y

BRAF Point Mutations in Primary Melanoma Show Different Prevalences by Subtype

Magnetic susceptibilities and electrical conductivities of (La, Sr)(Fe/Co)O x samples sintered in vacuo or in oxygen stream are measured here. Samples containing tetravalent magnetic ions in general have Curie contants smaller than those containing only trivalent ions. This fact and the high conductivity in the former specimens strongly support the combined effect of the double exchange and the usual exchange mechanism in these compounds. The parallel alignment of spins of magnetic ions due to double exchange is partly or completely hindered by the presence of the strongly negative trivalent-trivalent interionic interactions.

Hiroshi Watanabe

Papers

Magnetic Structure of SrFeO3

Magnetic Structure of SrCoO 2.5

Magnetic Properties of the System SrCo 1− x Fe x O 3− y

BRAF Point Mutations in Primary Melanoma Show Different Prevalences by Subtype

Magnetic Properties of Perovskites Containing Strontium : I. Strontium-Rich Ferrites and Cobaltites