Banca de DEFESA: FRANCISCO GOMES DE QUEIROZ

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : FRANCISCO GOMES DE QUEIROZ
DATA : 01/03/2023
HORA: 09:30
LOCAL: Auditório do PRODEP - Campus Central/Mossoró
TÍTULO:

Field and Temperature Effect on the Magnetic Phases of bulk and Films of the Rare Earths Dysprosium and Holmium.

PALAVRAS-CHAVES:

Magnetic phases; Thermal hysteresis; Rare Earth; Helimagnetic materials. 

PÁGINAS: 104
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física da Matéria Condensada
ESPECIALIDADE: Materiais Magnéticos e Propriedades Magnéticas
RESUMO:

Rare earth materials in their volumetric form without the presence of external field, only by thermal effects, present a rich diversity of magnetic configurations for certain temperature ranges, specific to each element. The construction of artificial systems, such magnetic thin films and multilayer, in which rare earth elements are part of at least one of the constituents, has promoted the discovery of new magnetic patterns.

In this work we present two investigations, one in collaboration with the experimental group of the magnetism laboratory of the Department of Physics of the Moscow State University M.V.Lomonosov in which we modeled the experimental results of ultrapure samples of the rare earth Dysprosium and the investigation of the thermal hysteresis cycles in holmium thin films of various dimensions, aiming to find different magnetic phases in these cycles.

The theoretical method used to obtain the equilibrium phases consists of a system, where the contributions of the exchange energies, anisotropy energy and zeeman energy are calculated in a set of nonequivalent magnetic spins, and the magnetic phases, from the temperature of Curie to the temperature of Nèel, are determined by self-consistent manner, resulting in a vanishing torque in the magnetic spins.

Our modeling reproduced the experimental measures of magnetization and magnetic phases obtained for the bulk Dysprosium. In the study for holmium thin films with dimensions of 7, 10, 12, 15, 18, 21 and 24 atomic planes, a width of thermal hysteresis is verified, varying from a value close to 18 K to approximately 100 K, depending on the intensity of the applied external magnetic field and the thickness of the film. For holmium thin films with dimensions less than 7 atomic planes thermal hysteresis is not observed.

MEMBROS DA BANCA:
Presidente - 1881 - VAMBERTO DIAS DE MELLO
Interno - 597.647.084-04 - DORY HÉLIO AIRES DE LIMA ANSELMO - UFRN
Externa ao Programa - 12268 - MARIA DAS GRAÇAS DIAS DA SILVA
Externo à Instituição - FRANCISCO CESAR DE MEDEIROS FILHO - UFERSA
Externo à Instituição - MANOEL SILVA DE VASCONCELOS - UFRN