Exploration of magnetism in 3D and 2D systems

Abstract

Magnetism has intruded in every aspect of our life, from electric motors to hard disk data storage to space technologies. Developing strong understanding of underlying magnetic properties is of utmost importance to reach new frontiers of technological advancement. During my Ph.D. research, I have explored complementary research venues in three dimensional as well as two dimensional materials to understand basic magnetic properties that were either not known or explored for the first time. In this quest, I have studied three different physical systems with overlapping structural and/or magnetic and electrical properties: nickel monosilicides (NiSi), cobalt-doped calcium ruthenate (Ca(CoxRu1-x)O3) and europium manganese arsenide (EuMn2As2). One of the key aspects of my research is to understand how magnetic moments correlate with each other. Understanding this fundamental question can help us in elucidating the mechanism behind novel magnetic proper-ties manifested by the above mentioned materials. While NiSi is found to manifest a new phenomenon of magnetism driven intermediate metallic-superconducting phase, (Ca(CoxRu1-x)O3) tends to exhibit the metal-insulator transition with the critical phase boundary coinciding with the onset of strong continuum type magnetic fluctuations. Despite the presence of strong dynamic magnetic moment correlation, no trace of any type of static magnetic order is detected in any of these materials. On the other hand, strong static order with two consecutive antiferromagnetic phase transitions are detected in the intertwined honeycomb structured EuMn2As2. During the process of studying bulk materials using macroscopic measurement techniques, I have acquired detailed knowledge of chemical synthesis methods and several experimental measurement techniques, including the analysis of magnetic susceptibility and neutron scattering methods. The gained knowledge is applied in pinpointing the low temperature magnetic phase transition in an ongoing project in the lab of two dimensional artificial magnetic (permalloy) honeycomb lattice. Two dimensional magnetic honeycomb lattice provides a unique platform to study emergent magnetic phenomena in reduced degrees of freedom. The system is expected to develop novel spin solid order at low temperature. I have performed detailed analysis of non-linear susceptibility of permalloy honeycomb lattice, which revealed the non-thermodynamic nature of phase transition to the spin solid state in this system. In the ensuing chapters, I have explained each project in great detail. A brief overview of the previous research works and the motivations behind the study is provided in the Introduction section.