The effect of oxygen isotope substitution on magnetic properties of (La1-yPry)0.7Ca0.3MnO3 manganites

Abstract

The effect of oxygen isotope substitution on the alternating-current magnetic susceptibility for (La1-yPry)0.7Ca0.3MnO3 ceramics (y = 0, 0.25, 0.5, 0.75, 1) was studied in the temperature range 4.2-300 K. At y < 0.75, the low-temperature behaviour of these manganites is typical for a ferromagnetic metal, whereas at y close to 1, the system behaves as an antiferromagnetic charge-ordered insulator. The 16O18O isotope substitution significantly shifts the Curie point TC, but has a smaller effect on the Néel temperature TN. At the crossover concentration y = 0.75, the exchange of 16O with 18O gives rise to a metal-insulator transition. The temperature dependence of the magnetic susceptibility is characterized by a pronounced hysteresis at y0 or 1, and the width of the hysteresis loops is strongly affected by the 16O18O exchange. The behaviour of the susceptibility in the paramagnetic phase gives an indication of the phase separation over quite a wide temperature range near the transition point. The phase diagram in the T-y plane is obtained and its modification with isotope substitution is discussed.