Spin-flop process identified in heteroepitaxial rare-earth films of Er and Ho

Abstract

Bulk-like heteroepitaxial Er, Ho, and Tb films were grown on alumina substrates. They show reduced magnetization that can be related to oscillation of moments returning an average magnetization due to the usual existence of conical, helical (cycloidal), and/or helifan phases along the temperature scale. Interestingly, below 20 K and at finite field values, the temperature of the conical phase in Er and Ho, we find the existence of various spin-flop processes due to the dominating degenerate bidirectional fluctuations arising from competing anisotropies within the conical phase. Plateaus in the magnetometric loops are identified as fingerprints of spin-flops in periodically arranged blocks of moments, which deviate from conventional spin-flop behavior in generic low-anisotropy antiferromagnets. Such spin-flops are manifestations of moments that are arranged in a pattern, comprising alternate blocks of regularly spaced members commensurate with the lattice. With a larger conical angle in Ho as compared to Er, the spin-flops occur more frequently, which provides an insight into how magnetic anisotropy can be manifested in rare-earth metals in realizing magnetic sub-states. By tailoring the conical structure, one can in principle regulate the magnetic sub-states in the future for applications.