Field-induced chirality in the helix structure of Ho/Y multilayers. Physical Review B. Condensed Matter and Materials

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The structural and magnetic properties of the multilayer holmium yttrium system are investigated by superconducting quantum interference device (SQUID) magnetometry and X ray and neutron scattering. The sample synthesized by molecular beam epitaxy is the Al 2 O 3 /Nb 50 Å /Y 200 Å /(Ho 60 Å /Y 30 Å ) × 30/Nb 50 Å layer sequence. The occurrence of a helical magnetic structure with a period of 24 Å and a spiral coherence length of about 500 Å is observed at a temperature of T N = 123 K upon the identical population of domains with left and right magnetic spirals after zero field cooling of the sample to a temperature of 10 K. The tran sition to the ferromagnetic structure at a temperature of 20 K in the investigated sample is suppressed.

Magnetic rare-earth / non-magnetic metal superlattices are well-known to display chiral spin helices in the rare-earth layers that propagate coherently across the non-magnetic layers. However, the underlying mechanism that preserves the magnetic phase and chirality coherence across the non-magnetic layers has remained elusive. In this Letter, we use resonant and element-specific x-ray scattering to evidence directly the formation of two fundamentally different long-range modulations in a Holmium/Yttrium (Ho/Y) multilayer: the known Ho chiral spin helix with periodicity 25Å, and a newly observed charge density wave with periodicity 16Å that propagates through both the Ho and non-magnetic Y layer. With x-ray circular magnetic dichroism measurements ruling out the existence of a magnetic proximity effect induced moment in the non-magnetic Y layers, we propose that the charge density wave is also chiral, thus providing the means for the transmittance of magnetic chirality coherence between Ho layers. * victor.ukleev@psi.ch

The dielectric properties of composite materials prepared by the embedding of ferroelectrics potassium dihydrogen phosphate (KDP), cesium dihydrophosphate (CDP), as well as antiferroelectric ammonium dihydrogen phosphate (ADP) into porous glass matrices with an average size of through pores of 7, 46, and 320 nm have been studied. It was found that an increase occurred in the phase transitions temperature (TC) for embedded particles in comparison with corresponding bulk materials. Some possible mechanisms of influence of “restricted geometry” on the Curie temperature are discussed. Estimates of TC shifting as a result of the “pressure effect” caused by elastic stresses in embedded particles as well as the result of bias electric field influence arising due to the piezoelectric effect are made. The possibility of using the tunneling Ising model to explain the experimental results is discussed.