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  • 1
    Electronic Resource
    Electronic Resource
    Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility (1995)
    Springer
    Journal of low temperature physics 100 (1995), S. 253-279 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured the nuclear specific heat Cn and nuclear susceptibility χn of In nuclei (I=9/2, μ=5.5μ n) in the cubic intermetallic compound AuIn2 (Korringa constant κ=0.11 Ksec) in the normal conducting state at 30μK⩽10mK and 2mT⩽B⩽115 mT. Our data show a positive nuclear Weiss temperature θ=+ 43 μK and that the In nuclei undergo a nuclear ferromagnetic transition at Tc=35 μK. The In nuclei experience an internal field of about 10 mT (obtained from Cn at T〉Tc ). The nuclear ordering temperature Tc and the internal field increase with applied magnetic field. From the data we deduce exchange constants for the investigated system. The critical entropy reduction ΔS(Tc)/Smax=8.6% and critical enthalpy ΔE=0.28 RTc are in reasonable agreement with the measured ordering temperature Tc,applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time τ calculated from the real and imaginary parts of χ n is 10 msec at T〉50 μK, but drops to τ〈1msec at Tc.This is the first observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T nuclear =T electron .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00751510
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  • 2
    Electronic Resource
    Electronic Resource
    Van vleck paramagnetism of the diluted intermetallic compounds Pr1−x Y x Ni5 at fields up to 15 T (1997)
    Springer
    Journal of low temperature physics 107 (1997), S. 209-224 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured the 16 Hz susceptibility of the diluted Van Vleck paramagnets Pr1−x Y x Ni5 withx=0.00, 0.05, 0.10. 0.20 at temperatures 1.5 K≤T≤50 K and magnetic fields up to 15T. Their Van Vleck type magnetic susceptibility χ(T, B, x) strongly depends on the field atB≥6 T. The temperatureT max(B, x) of the maximum of χ(T, B, x) decreases at increasing the field from zero to 15 T by approximately one order of magnitude for all Pr1−x Y x Ni5 compounds. Changing the dilutionx from zero to 0.20, the field whereT max(B, x) strongly drops is increased from 9 T to 11 T. Our data agree qualitatively with the predictions of a point charge model which considers the Zeeman term in addition to the electronic exchange and the dominating crystal field contributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396842
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  • 3
    Electronic Resource
    Electronic Resource
    Static Nuclear Magnetisation of Aluminium Measured by Its Influence on the Superconducting Critical Field (1998)
    Springer
    Journal of low temperature physics 110 (1998), S. 363-368 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured the temperature dependence of the superconducting critical field of Al in the temperature range 17μK ≤ T ≤ 600mK. The external magnetic field necessary to suppress superconductivity in Al decreases significantly with decreasing T below about 1 mK. This effect is due to the paramagnetic contribution of the nuclear magnetic moments of Al to the total magnetic flux. Our method enables us to determine the static nuclear magnetisation of the Al nuclei. The results are in agreement with the theory for a Langevin nuclear paramagnet. In addition, we have measured the spin lattice relaxation time τ 1 . For the Korringa constant we get τ 1 ·T = (2.0±0.2)K sec in good agreement with previous NMR results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022501220362
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  • 4
    Electronic Resource
    Electronic Resource
    Interplay of Nuclear Magnetism and Superconductivity (1998)
    Springer
    Journal of low temperature physics 110 (1998), S. 405-410 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ratio of nuclear saturation magnetization and superconducting critical field, μ 0 M sat / B S0*≡∈, classifies the strength of mutual influence of nuclear magnetism and superconductivity. In order to investigate the interplay of both phenomena for the three distinct cases ∈ ≪ 1, ∈ ≍ 1, and ∈ ≫ 1 we have measured the ac susceptibility of Al, of the intermetallic compound AuIn 2 , and of the metal hydride TiH 2.07 at ultralow temperatures, 17 μK ≤ T ≤ 1 K, as function of static field 0 ≤ B ≤ 15 mT. For Al, the interplay enables an absolute measurement of the nuclear magnetization. For AuIn 2 , we get a steep decrease of B S (T) and a broadening of the superconducting transition in its nuclear ferromagnetic phase. Surprisingly, the nuclear ferromagnetic state coexists with type-I superconductivity in AuIn 2. The metal hydride TiH 2.07 , which is under present investigation, is a good candidate to show reentrant superconductivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022565607158
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  • 5
    Electronic Resource
    Electronic Resource
    Magnetic properties of Ag sinters and their possible impact on the coupling to liquid3He at very low temperatures (1997)
    Springer
    Journal of low temperature physics 106 (1997), S. 581-590 
    Details
    ISSN: 1573-7357
    Keywords: 67.50.-b ; 67.60.-g ; 75.20.-g ; 75.60.Jp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on measurements of the magnetization of metal sinters made of different Ag powders with average (nominal) grain sizes of 40nm and 70nm at1.6K≤T≤250K and0≤B≤6T. Besides the dominating diamagnetism of Ag, the sinters show unexpected magnetic properties; e.g. once exposed to a magnetic field B, the sinters keep a permanent magnetic moment (in zero external field) which strongly depends on the magnitude of B. The possible impact of the unexpected magnetic properties of the Ag sinters on various experimental observations at very low temperatures, e.g. the magnetic field dependence of the thermal boundary resistance between an Ag sinter and3He at millikelvin temperatures is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02395924
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic properties of highly dilutedPdFex andPtFex-alloys. Part I. Magnetization at kelvin temperatures (1996)
    Springer
    Journal of low temperature physics 104 (1996), S. 49-65 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Localized 3 d magnetic moments polarize in palladium and platinum matrices the Pd 4d and Pt 5d conduction electrons in their neighbourhood. This leads to effective “giant magnetic moments” μgm. We have measured the magnetization M(x, B, T) of each ninePdFex andPtFex samples with 2ppm≤x≤260ppm at 1.6K≤T≤300 K and 0 ≤B ≤ 6.0 T. Our main motivation is to determine the size of the giant magnetic moments induced by highly diluted Fe impurities in both transition metals. From the data, taken in a wide polarization range, 9% ≤M/Msat≤93%, we determine the impurity concentrations x, the effective moments μgm, and the spin quantum number J of the samples by fitting to the Brillouin function. ForPdFex, we find a slight increase of μgm with concentration from (13 ± 1.5) μB at x = (2.5 ± 0.5) ppm to (16 ± 1) μB at x = (220 ± 30) ppm. ForPtFex, the moments are almost constant with μgm = (7.8 ± 1) μB at x = 2 to 14 ppm and μgm = (8.6 ± 0.7) μB at x = 75 to 95 ppm. For all samples we obtain a concentration independent very large or possibly infinite spin quantum number, J ≥ 100, which means that the localized giant moments behave as classical ones at T 〉 1.6 K and Tesla magnetic fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754089
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic properties of highly dilutedPdFex andPtFex-alloys. Part II. Susceptibility at micro- and milli-kelvin temperatures (1996)
    Springer
    Journal of low temperature physics 104 (1996), S. 67-94 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured the 16 Hz susceptibility of the giant magnetic moments induced by Fe impurities in highly dilutedPdFex andPtFex samples with 2.5 ppm ≤ x ≤ 75 ppm in a wide temperature range, 30 μK≤ T ≤ 300 mK, and at static magnetic fields 0,01 mT≤ B ≤ 25 mT. We find spin glass freezing at Tf(X)/X≅0,19mK/ppm Fe forPdFex and the larger value 0.26 mK/ppm Fe forPtFex. This is the first observation of spin glass freezing inPtFex. In the low-temperature range T ≲ 0.5Tf(x), the susceptibilities follow χ — χ0∽ T with small zero-temperature χ0 values forPdFeX and vanishing χ0 values forPtFex. In the paramagnetic high-temperature range, we find χ℞(T — θ)it-1 at T ≥ 10 mK independent of x forPdFex, and at T ≥ 2Tf(x) dependent of x forPtFex with vanishing θ values for both systems. The data compare well to the predictions of the Thouless-Anderson-Palmer “TAP” approach of the Sherrington-Kirkpatrick “SK” model for spin glasses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754090
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  • 8
    Electronic Resource
    Electronic Resource
    The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures (1998)
    Springer
    Journal of low temperature physics 111 (1998), S. 99-118 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mT≤B≤248 mT. The susceptibility data have been measured at temperatures of 0.3 μK≤T≤100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 μK. The nuclear heat capacity data taken at 1.4 μK≤T≤10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 μK. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 μK≤T≤0.5 mK and 2.5 mT≤B≤22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 μK≤T≤0.5 mK and at 5.4 mT≤B≤200 mT. Spin-lattice and effective spin-spin relaxation times τ 1and τ 2 * of 195 Pt strongly depend on x and on the external magnetic field. No temperature dependence of τ 1and τ 2 * could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 μK.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022250325324
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  • 9
    Electronic Resource
    Electronic Resource
    Magnetic Impurities in Glass and Silver Powder at Milli- and Microkelvin Temperatures (2000)
    Springer
    Journal of low temperature physics 118 (2000), S. 45-57 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In search of an ideal paramagnet for thermometry at very low temperatures, we have studied the magnetic behaviour of impurity moments (localized Fe3+, impurity concentration x = (180±10) ppm) dissolved in a structural borosilicate glass, in the temperature range 0.07 ≤ T ≤ 300 mK by means of dynamic ac susceptibility, and at 1.6≤T ≤ 300 K by static dc magnetization. In order to improve the thermal coupling of the insulating glass at the lowest temperatures, it was pulverized and mixed with silver powder of submicron grain size; the composite was subsequently compacted to a cylindrical sample by applying a pressure of a few kbar. This contact method which is applicable to other materials with bad thermal conductivity as well improved the accessible minimum temperature for the glass down to ≃0.1 mK. At low temperatures, we observe a Curie Weiss law for the dynamic susceptibility χ of the magnetic Fe3+ impurities in the glass down to ≈0.6 mK, a broad maximum of χ at T ≃ 0.38 mK and a decrease towards even lower temperatures. Compared to the frequently used, highly diluted metallic spin glasses, the magnetic behaviour of the glass makes inductance thermometry applicable in a much larger temperature range. In addition, we have investigated the low temperature magnetic properties of a sample of compacted silver powder. The small amount of paramagnetic impurities in the Ag particles (x = (4 ± 1) ppm) exhibits a low temperature susceptibility which can be described by the Kondo effect with an unexpectedly small Kondo temperature of T K ≃ 1 mK.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004674402736
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  • 10
    Electronic Resource
    Electronic Resource
    Nuclear ferromagnetic ordering of141Pr in the diluted Van Vleck paramagnets Pr1−x Y x Ni5 (1994)
    Springer
    Journal of low temperature physics 97 (1994), S. 189-211 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on the first investigation of the effect of “magnetic dilution” on nuclear magnetic spin interactions in metals; we studied this effect in the diluted Van Vleck paramagnets Pr1−xYxNi5. In addition, we investigated the electronic magnetic properties of these intermetallic compounds. For this purpose, we have measured the nuclear and electronic susceptibilities of Pr1−xYxNi5 with x = 0 to 0.2 at 50μK ⩽ T ⩽8 mK and at 2.2 K ⩽ T ⩽ 300 K. We observe a linear decrease of the electronic Van Vleck susceptibility and of the hyperfine enhancement factor by 13% (per mole Pr3+). The hyperfine-enhanced nuclear susceptibility decreases by about a factor of three when going fromx = 0 tox = 0.2. The samples show nuclear ferromagnetic transitions of141Pr with nuclear Curie temperatures Tc decreasing from 370 μK to 100 μK and Weiss temperatures Θ decreasing from 218 μK to 13 μK in this concentration range. These data are compared with the results of mean-field calculations. In addition, we report on measurements of the nuclear spin relaxation time τ of these compounds, for which we find values of a few msec at millikelvin temperatures and a critical speeding-up at Tc. Our data give hints that for x 〉 0.2 the character of the nuclear magnetic transition may change, possibly to a nuclear spin glass freezing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00752985
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