1989 Fiscal Year Final Research Report Summary
Development of a new method producing very low temperatures with manganese-zeolite
| Project/Area Number |
63550004
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Applied materials
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| Research Institution | University of Tsukuba |
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Principal Investigator |
NARAHARA Yoshimasa Inst. of Phys., Univ. of Tsukuba Professor, 物理学系, 教授 (40015508)
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| Co-Investigator(Kenkyū-buntansha) |
TOMINAGA Akira Inst. of Phys., Univ. of Tsukuba Assistant Professor, 物理学系, 講師 (10015563)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Mn-zeolite / Curie-Weiss law / phase transition / relaxation mechanism / long-range correlation / dipolar interaction / magnetic ordering / adiabatic demagnetization |
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| Research Abstract |
Our sample, Mn-zeolite was fabricated substituting some of sodium ions for manganese ions in zeolite-Y, Na_<50> (AlO_2)_<50> (SiO_2)_<142> 25OH_2O (the product of Tosoh Co.). Concentration of Mn^<2+> was measured by chemical analysis, ICP-OES and X-ray microanalysis. Most Mn^<2+> were found to exist in supercages from the results of X-ray diffraction and EXAFS and likely to distribute fairly uniformly in the samples. Mn^<2+> concentrations and average distances between ions of our two samples are 10^<-3> mol/g, 9.4 A and 10^<-4> mol/g, 20 A respectively.
Temperature dependence of susceptibility was measured from 300 K to 20 mK. Curie-Weiss law is satisfied from 300 K to 50 mK in our sample of higher concentration (Curie constant: 4.0 x 10^<-3> emu/g; Weiss temperature: -50 mK). The effective magnetic moment of Mn^<2+> is 5.58 mu_B close to that of free Mn ions. Susceptibility has maximum around 30 mK which shows that phase transition takes place. Temperature and frequency dependence of
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the susceptibility below 1 K shows that relaxation mechanism is governed not by a single relaxation time, but distributed relaxation times. Especially Cole equation with consideration of long-range correlation between spins explains results below 40 mK.
ESR experiment was performed from 300 K to 40 mK. g value is 2 and line width is also independent of temperature. Interaction between ions is mainly dipolar interaction. The line width in X-band is 650 gauss which is interpreted as the sum of 220 gauss of dipolar and 430 gauss of hyperfine interaction. Magnetic ordering at low temperatures is mainly due to this dipolar interaction.
Performing adiabatic demagnetization with initial conditions of 1.3 K and 5 T, we obtained about 80 mK. The lattice temperature of Mn-zeolite follows well the spin temperature down to this temperature. Internal field of this sample is considered to be small since the temperature produced is nearly proportional to the external field down to the minimum temperature. Less
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