Abstract
Simultaneous magnetization and magnetoresistance measurements have yielded the magnetic phase diagram of the granular Co-SiO2 system. The superparamagnetic-to-ferromagnetic transition temperature changes gradually with composition from 80 K at 20 vol% Co to 280 K at 43 vol% Co. The results confirm the theory of spindependent tunneling in granular magnetic metals and yield the value of JP=(1.0±0.3) meV. Here P is the spin polarization of the tunneling electrons and J their exchange-coupling constant. This quantity has not been measured previously for cobalt. A quantitative comparison shows that the molecular-field theory does not provide an adequate description of the magnetization of granular cobalt.
Original language | English |
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Pages (from-to) | 1809-1817 |
Number of pages | 9 |
Journal | Physical Review B |
Volume | 23 |
Issue number | 4 |
DOIs | |
State | Published - 1981 |