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Habilitation Thesis
DOI
10.11606/T.43.2015.tde-27072015-163924
Document
Author
Full name
Nei Fernandes de Oliveira Junior
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1968
Committee
Sala, Oscar (President)
Barros, Fernando de Souza
Hamburger, Ernst Wolfgang
Oliveira, Sergio Mascarenhas
Swieca, Jorge André
Title in Portuguese
Um criostato para medida de susceptibilidade magnética entre 20° K e 0,3° K. Susceptibilidade magnética dos halogenetos e do nitrato de níquel hexa-amoniacais
Keywords in Portuguese
Baixa temperatura
Física dos materiais
Física mecânica
Abstract in Portuguese
Nêste trabalho descrevemos uma aparelhagem experimental para a medida de susceptibilidade magnética em qualquer temperatura entre 0,3°K e 20°K ininterruptamente. Com esta aparelhagem medimos a susceptibilidade de amostras em pó dos halogenetos e do nitrato de níquel hexa-amoniacais (NiCL2 6NH3 , NiBr2 6NH3 , NiI2 6NH3 e Ni (NO3)2 6NH3). Nas temperaturas do hidrogênio êstes sais obedecem estritamente uma lei de Curie-Weiss da qual extraímos os fatores espectroscópicos e temperaturas de Weiss: G ɵ NiCL2 6NH3 2,175 ± 0,010 -8,6 ± 0,3 NiBr2 6NH3 2,177 ± 0,013 -6,1 ± 0,3 NiI2 6NH3 2,187 ± 0,012 -2,9 ± 0,2 Ni (NO3)2 6NH3 2,188 ± 0,010 -3,3 ± 0,2 Estes parâmetros concordam com medidas anteriores de ressonância paramagnética e susceptibilidade magnética. No NiCl2 6NH3 e no NiBr2 6NH3 observamos um comportamento anômalo nas temperaturas em que medidas de calor específico indicam uma transição antiferromagnética. No Ni (NO3)2 6NH3 observamos um pico característico de transição antiferromagnética a 1,7°K com a susceptibilidade tendendo a 2/3 do valor de pico na parte de baixas temperaturas. A razão ɵ/TN é da ordem de -2 o que contraria uma regra experimental observada para antiferromagnética de estrutura f.c.c. (ɵ ~ -10 TN).
Title in English
A cryostat for measuring magnetic susceptibility between 20 ° K and 0.3 ° K. Magnetic susceptibility of halides and nickel nitrate hexahydrate ammoniacal
Keywords in English
Low temperature
Mechanics physics
Physics of materials
Abstract in English
In this work we describe some experimental apparatus for the measurement of magnetic susceptibility in the temperature range between 0,3°K and 20°K. With this apparatus we measured the susceptibility of powdered samples of the halides and nitrate of the nickel hexamine (NiCL2 6NH3 , NiBr2 6NH3 , NiI2 6NH3 e Ni (NO3)2 6NH3). At the hydrogen temperatures these salts obey a Curie-Weiss law from which we have extracted the following spectroscopic factors and Weiss temperatures: G ɵ NiCL2 6NH3 2,175 ± 0,010 -8,6 ± 0,3 NiBr2 6NH3 2,177 ± 0,013 -6,1 ± 0,3 NiI2 6NH3 2,187 ± 0,012 -2,9 ± 0,2 Ni (NO3)2 6NH3 2,188 ± 0,010 -3,3 ± 0,2 These parameters agree with published data from paramagnetic resonance and magnetic susceptibility. In the NiCL2 6NH3 and NiBr2 6NH3 we observed an anomalous behavior at the temperatures where specific heat measurements indicate an antiferromagnetic transition. In the Ni (NO3)2 6NH3 we observed a peak at 1,7°K characteristic of an antiferromagnetic transition, with the susceptibility tending to 2/3 of the peak value in the low temperature side. The ratio ɵ/TN is of the order of -2; this desagrees with an experimental rule for f.c.c. antiferromagnets (ɵ ~ -10 TN).
 
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RE46261OliveiraJr.pdf (7.63 Mbytes)
Publishing Date
2015-07-31
 
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