Low-temperature magnetoresistance and magnetic ordering in

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Abstract
In zero field, shows thermally activated behaviour for all values of x. For charge ordering occurs at 250 K, with long-range antiferromagnetic ordering at lower temperatures. For a range of compositions a first-order magnetic-field-induced insulator - metal transition produces changes in resistivity of up to 12 orders of magnitude at low temperatures. These conducting states are metastable, resulting in a large hysteresis in resistivity with changes in both magnetic field and temperature. There is a marked relationship between the resistivity and the magnetic state of the material. Below the charge-ordering temperature, metamagnetic transitions occur which transform the magnetic correlations from either paramagnetic or antiferromagnetic to ferromagnetic. The range of compositions for which these metamagnetic transitions occur, the fields required to induce the ferromagnetic state, and the irreversible changes in the nature of the magnetic ordering all correlate with the field-induced changes in resistivity.