Lanthanum magnetic measurements

A complete study of three systems has been carried out using several techniques such as X-ray diffraction, electron microscopy, Mossbauer spectroscopy, magnetic measurements, and electrical conductivity. Two methods have been used to create anionic defects - replacement of lanthanum by calcium or strontium in Lai 2yCa2yFem03 y and La1 2ySr2yFein03-y - replacement of titanium by trivalent iron in CaTi1 2yFe2y03 y. 

There is much interest in this superconductor for two reasons. Measurements of the effect of pressure on the material indicate that the onset transition temperature increases to 147 K when the pressure is raised to 230000 times atmospheric pressure (23.5giga Pascal). The result excited many researchers because pressure on a material can be created chemically by replacing some fraction of an ion by a similar ion of smaller radius. The obvious choice in this case was to replace the larger barium with smaller strontium. This had worked with the lanthanum compound discussed earlier. Unfortunately nature is not always so predictable. Replacement of barium by strontium reduced Tc to 127 K instead of increasing it beyond 133 K. The other reason for the interest in this material seems much more important. Resistance measurements in dc magnetic fields have shown... 

The critical magnetic field curve measurements of lanthanum and yttrium-thorium sesquicarbide (Francavilla et al. 1976, Francavilla and Carter 1976) show that the initial slopes of the critical magnetic field curve are (2.4 0.2) x lO OeK" and... 

Nuclear magnetic relaxation rates have been used to investigate the coordination number. In an investigation of the line-width broadening of La in various perchlorate solutions, Nakamura and Kawamura (1971) attributed the decreases in the values of (Av is the relaxation rate and is the relative viscosity) to a possible equilibrium between the nonahydrates and octahydrates for lanthanum ion. This conclusion was disputed by Reuben (1975) who proposed that this apparent anomaly reflected an erroneous estimate of the corrections of the linewidths for peaks due to the effect of the finite modulation amplitude and/or of partial saturation. Measurement of the transverse relaxation rates by the pulse method gave results consistent with a constant hydration number for lanthanum ion (Reuben 1975). 

In this review we have not touched on the related metals yttrium and scandium. We may briefly mention here that recent measurements give results in line with those for non-magnetic lanthanum and lutetium. For yttrium the most recent results give y - 8.2 mJ/mole-K and 6d(0) = 248 3 K (Wells et al., 1976), while for scandium y = 10.34 mJ/mole-K and SofO) = 346.1 0.9K (Tsang et al., 1976b). 

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