Search for: All records

The magnetic properties and phase diagrams of S = 1/2 quasi-one-dimensional Heisenberg antiferromagnets are well established with copper-containing coordination polymers as the platform of choice due to their low energy scales and ease of chemical substitution. The inability to uncover orbitally resolved components of the magnetization has, however, been a longstanding barrier to greater understanding of high field spin state transitions. In this work, we combine pulsed field magnetization, optical spectroscopy, and magnetic circular dichroism with complementary electronic structure calculations to unravel orbital-specific contributions to the magnetism in the linear chain quantum magnet [CuL2(H2O)2(pyz)](ClO4)2 [L = 5-methyl-2-pyridone; pyz = pyrazine]. In addition to revealing a spin flop and field-driven transition to the fully saturated spin state, we untangle the green → teal color change across the 185 K structural phase transition and employ what we learn about the different Cu2+ → pyrazine charge transfer excitations to decompose the magnetic circular dichroism. Analysis reveals that both eg-derived Cu2+ 3d orbitals play a role in the field-driven transition to the fully saturated state, not just those formally hosting unpaired electrons. We attribute the surprisingly strong dichroic signature at room temperature to the presence of uncorrelated spin. 

Abstract Hafnia (HfO 2 ) is a promising material for emerging chip applications due to its high- κ dielectric behavior, suitability for negative capacitance heterostructures, scalable ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO 2 crystals stabilized with yttrium (chemical formula HfO 2 :  x Y, where x  = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO 2 and paves the way for an analysis of mode contributions to high- κ dielectric and ferroelectric properties for chip technologies.