Fe 2 O 3 nanoparticles embedded in a SiO 2 matrix have been synthesized by sol-gel chemistry and high temperature heat treatments. Virtually pure -Fe 2 O 3 (in excess of 93%) is obtained, although a two-phase mixture, -Fe 2 O 3 + R-Fe 2 O 3 , is observed for Fe 2 O 3 /SiO 2 ratios greater than 37 wt %. The -Fe 2 O 3 nanoparticles are stable up to ∼1600 K. Optimized -Fe 2 O 3 nanoparticles are ferrimagnetic, with a Curie temperature T C ≈ 510 K, and remarkably high values of room-temperature coercivity, H C ) 20 kOe.

In the manganite N d 0.5 Ca 0.5 M nO 3 , charge ordering occurs at much higher temperature than the antiferromagnetic order (T CO = 250K, T N = 160K).the magnetic behavior of the phase T N < T < T CO is puzzling: its magnetization and susceptibility are typical of an antiferromagnet while no magnetic order is detected by neutron diffraction.We have undertaken an extensive study

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