Magnetoelasticity and structure of Er/Y superlattices

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Abstract
Single-crystal superlattices (Erx/Yy) have been grown by molecular-beam epitaxy techniques with the c axis perpendicular to the growth plane. The magnetic structure has been determined by neutron diffraction, and demonstrates long-range order of the c-axis Ising-like Er moments extending through the ‘‘magnetically dead’’ Y layers (TN superlattice ≊TN bulk), as was found for the X-Y superlattices (Dyx /Yy). The Er c-axis effective turn angles for x=13, 23, and 32 are all nearly temperature independent at ω≊2π/7, the high-temperature lock-in value in bulk Er (although it is difficult to determine if a lock-in transition occurs), with the ferromagnetic transition completely suppressed. This results from the fact that the magneto-elastic energy density, which causes ω to decrease in the bulk, is considerably reduced in the superlattices. As in bulk Er, the high-temperature sinusoidally modulated phase ‘‘squares up’’ upon reducing the temperature, and this squaring is enhanced at the basal-plane ordering transition, which is at roughly half the temperature found in bulk Er. The basal-plane turn angle tends towards the low-temperature value of bulk Er, ω≊π/4, which is surprisingly different from the c axis ω.