Theoretical studies of pressure effects on the magnetic and electronic properties of the weak roving ferromagnetic compound 𝑆𝑐3𝐼𝑛.

Name: Deivid Wilson Oliveira Santana
Type: PhD thesis
Publication date: 08/12/2022

Namesort descending Role
Jorge Luis Gonzalez Alfonso Co-advisor *
Wanderlã Luis Scopel Advisor *

Examining board:

Namesort descending Role
Fabio Arthur Leão de Souza External Examiner *
Flávio Garcia External Examiner *
Jorge Luis Gonzalez Alfonso Co advisor *
Valberto Pedruzzi Nascimento Internal Examiner *
Wanderlã Luis Scopel Advisor *

Summary: Materials labeled as weak itinerant ferromagnetic, composed of non-magnetic elements, are rare and intriguing. Therefore, the study of this physical system represents a challenge in condensed matter physics. Their representatives are the compounds 𝑆𝑐3𝐼𝑛 and 𝑍𝑟𝑍𝑛2. In these systems, the unpaired electrons of the 3𝑑 bands play a major role in their magnetic properties. Experimental results show that the main magnetic characteristics of these compounds are the low magnetic moment and low critical Curie temperature (𝑇𝑐). In the case of 𝑆𝑐3𝐼𝑛, an increase in the magnetic properties of this compound was experimentally detected, such as the Curie temperature and magnetic moment when subjected to hydrostatic pressure. This behavior is anomalous to ferromagnet compounds and unraveling the mechanism that underlies this phenomenon is one of the topics addressed in this thesis work. Our approach will be theoretical, using first principles calculations through Density Functional Theory (DFT) to simulate the effects of applied pressures on the electronic structure, and study the electronic, magnetic and structural properties of 𝑆𝑐3𝐼𝑛 together with the Stoner`s theory, corrected by Moriya`s spin fluctuation renormalization theory. Theoretical calculations at ambient pressure confirm the role of electrons that occupy the 𝑑−𝑆𝑐 orbitals in the origin of the magnetic and electrical properties of this studied compound. Our results show the decrease in the magnetic moment of the scandium atom under hydrostatic pressure and in its density of unpolarized states for the 𝑑−𝑆𝑐 orbitals at Fermi energy. These results are combined with the theoretical Moriya-Kawabata model and experimental results to explain the dependence of 𝑇𝑐 with pressure application. In this sense, our results conclude that the increase in the Curie temperature, with the pressure 𝑑𝑇𝑐/𝑑𝑃, observed in experimental results, is related to the increase in the electron-electron exchange interaction 𝐼 between the conduction electrons that occupy the bands 𝑑−𝑆𝑐 of the compound 𝑆𝑐3𝐼𝑛.

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