Temperature and thickness dependence of the magnetization reversal in DyFe2/YFe2 exchange-coupled superlattices

DyFe₂/YFe₂] superlattices have been grown by Molecular Beam Epitaxy. The magnetic properties of this hard/soft composite system, the components of which are exchange-coupled at the interfaces, have been investigated in the 10 K–300 K temperature range, with a specific attention paid to the influence of the soft and hard materials thicknesses. In order to unravel the very rich magnetization reversal processes, conventional susceptibility and magnetization measurements have been combined with element-selective X-ray Magnetic Circular Dichroism analysis. The superlattice with thin individual thicknesses ( 1nm DyFe₂/4 nm YFe₂] ₇₀) reverses as a unique giant ferrimagnetic block in which the exchange-favoured antiparallel arrangement between net magnetizations is maintained under a magnetic field. In the superlattices with large individual thicknesses ( 10 nm DyFe₂/13 nm YFe₂] ₁₈ and 10 nm DyFe₂/20 nm YFe₂] ₁₃), the expected exchange spring behaviour is observed: the soft YFe₂ layers reverse for positive bias fields, followed by the irreversible switch of the hard DyFe₂ layers. In the case of intermediate thickness for the individual DyFe₂ layers ( 3 nm DyFe₂/12 nm YFe₂] ₂₂, 5 nm DyFe₂/20 nm YFe₂] ₁₃, 7 nm DyFe₂/28 nm YFe₂] ₁₀), the magnetization reversal process strongly depends on temperature. In particular, an unusual magnetization reversal process occurs in the high temperature range where it becomes easier to reverse the hard DyFe₂ layers for positive fields, while maintaining the dominant YFe₂ magnetization along the field direction.