Ground state of nuclear spins in fcc metals

Viertiö, H. E.; Oja, Aarne

doi:10.1103/physrevb.36.3805

Cited by 37 publications

(9 citation statements)

References 15 publications

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“…The results in Fig. 116 are in fairly good agreement with the earlier spin-wave calculation of Viertiö and Oja (1987), except for structure 3, which was not investigated in their work. In comparison with the earlier perturbation calculation of Lindgå rd (1988a) there is good overall agreement for mϽ0.8 except for the fact that the triple-k structure does not generally have the symmetric form of Eq.…”

Section: A Bʈ[001]supporting

confidence: 86%

“…The experimental result was analyzed in several theoretical calculations (Kjä ldman and Kurkijä rvi, 1979;Oja and Kumar, 1984;Kumar et al, 1985Kumar et al, , 1986Viertiö and Oja, 1987;Frisken and Miller, 1988a;Lindgå rd, 1988a). However, it was not possible to test the proposed spin structures against experiments, since measurements of static susceptibility do not yield sufficiently detailed information.…”

Section: B Theoretical Surveymentioning

confidence: 99%

“…For type-I fcc antiferromagnets with isotropic interactions, the spin-wave calculation of Oguchi et al (1985) first showed that quantum fluctuations favor a single-k structure instead of, for example, a triple-k configuration. Effects due to dipolar anisotropy as well as configurations caused by the external magnetic field were first discussed by Viertiö and Oja (1987), who also employed spin-wave theory. The same problems were later investigated by Lindgå rd (1988a, 1988b), using perturbation theory, and more recently by Heinilä and Oja (1993a).…”

Section: Overview Of Fluctuation Mechanismsmentioning

confidence: 99%

“…The first theoretical studies were made by Viertiö and Oja (1987), who used the linear spin-wave theory to calculate the quantum-mechanical correction to the ground-state energy, viz.,…”

Section: Anisotropic Spin-spin Interactions With An Easy Planementioning

confidence: 99%

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Nuclear magnetic ordering in simple metals at positive and negative nanokelvin temperatures

1997

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This paper is a comprehensive review of almost twenty years of research on nuclear magnetic ordering, first in copper and later in silver and rhodium metals. The basic principles of nuclear magnetism and the measurement of positive and negative spin temperatures are discussed first. Cascade nuclear refrigeration techniques, susceptibility and nuclear-magnetic-resonance (NMR) measurements, and arrangements for neutron-diffraction experiments at nanokelvin and picokelvin temperatures are described next. Comprehensive magnetic-susceptibility and neutron-diffraction measurements on copper, which led to the discovery of at least three antiferromagnetic phases, one displaying the novel (0 2 3 2 3 ) spin structure and the other two showing the type-I order of the fcc system, are then described in detail. NMR data on silver, at TϾ0 and TϽ0, are presented next leading to the observation that silver orders antiferromagnetically at positive spin temperatures and ferromagnetically at negative spin temperatures. The authors discuss recent neutron-diffraction measurements that show that the antiferromagnetic structure at TϾ0 is in a single-k type-I state. NMR data on rhodium at TϾ0 and TϽ0 are also described. Results obtained on Tl, Sc, AuIn 2 , and metallic Pr compounds and on insulators like CaF 2 are then discussed briefly. The paper is concluded by an extensive theoretical section. Calculations of conduction-electron mediated exchange interactions are described, and the mean-field theory of nuclear magnetic ordering is presented. The role of thermal and quantum fluctuations is then discussed, particularly in the selection of the antiferromagnetic ground state. Finally, theoretically calculated magnetic phase diagrams and ordered spin structures of copper and silver are presented in detail and compared with experimental results. The overall agreement is good, affirming the value of nuclear magnets in Cu and Ag as realizations of simple physical models. [S0034-6861(97)00301-2] ogy,

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Section: A Bʈ[001]supporting

confidence: 86%

Section: B Theoretical Surveymentioning

confidence: 99%

Section: Overview Of Fluctuation Mechanismsmentioning

confidence: 99%

“…The first theoretical studies were made by Viertiö and Oja (1987), who used the linear spin-wave theory to calculate the quantum-mechanical correction to the ground-state energy, viz.,…”

Section: Anisotropic Spin-spin Interactions With An Easy Planementioning

confidence: 99%

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Nuclear magnetic ordering in simple metals at positive and negative nanokelvin temperatures

1997

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“…More distant /'s were neglected, since their strengths are at most 14% of the nearest-neighbor value according to a recent first-principles calculation. 9 We find that h 2 A 2~ \\J 2 + x a Xb(Y a -7b) 2 h 2 B 2 , if / is sufficiently large, i.e., J/h > 20 Hz. The second term, caused by the presence of two isotopes, is small in the investigated field region, which justifies our approximation of an effectively single-isotope system.…”

Section: Jjv{mentioning

confidence: 97%

Cross relaxation by single spin flips in silver at nanokelvin temperatures

Oja¹,

Annila²,

Takano³

1990

Phys. Rev. Lett.

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The cross-relaxation time x x between the Zeeman temperatures of the 107 Ag and 109 Ag spin species in silver metal has been measured over five decades at low nanokelvin temperatures as a function of the external magnetic field B. Besides increasing with B, r x decreases with spin polarization. From the data, the strength of the Ruderman-Kittel interaction between the nuclei is determined. These experiments demonstrate that thermal equilibrium is not reached via mutual flips of unlike spins but in much slower processes involving single spin flips, caused by the dipolar interaction.PACS numbers: 76.60.Es Cross relaxation (CR) in spin systems has been investigated extensively since an NMR experiment by Abragam and Proctor 1 and papers by Pershan and coworkers. 2,3 Subsequently, Provotorov 4 developed a rigorous quantum-statistical theory which has since been verified in a large number of experiments. With the exception of early studies, however, the majority of the works has been concerned with rotating-frame Zeeman systems in spin-locked NMR. 5 The present study addresses some of the fundamental questions in CR by using a conceptually simpler case involving two laboratory-frame Zeeman systems and by extending the experimentally investigated realm to orders of magnitude lower temperatures.In this Letter, we report an NMR experiment in silver metal at submicrokelvin temperature and in low magnetic fields. Silver is ideally suited for the investigation of CR: Its large Korringa constant z\T e = \0 secK results in a long spin-lattice relaxation time x\ (14 h in our experiment), allowing studies of slow processes. Both isotopes l07 Ag and ,09 Ag have /= y and, therefore, quadrupolar effects are absent. We have measured the crossrelaxation time x x between the two spin species, which covers five decades. Besides showing the expected increase with the field, x x decreases with spin polarization; this is a new effect. The low-polarization x x allows us to extract the strength of the Ruderman-Kittel 6 (RK) exchange interaction between the silver nuclei. This is a quantity of particular interest: First, the RK interaction provides an important test for first-principles electronic structure calculations 7 " 9 because of its sensitive |yK0)| 4 dependence on the electronic wave function y/(r) at the nuclear site. Second, the RK coupling is expected to influence strongly the spin structure of the antiferromagnetic phase predicted for silver at temperatures below 0.5 nK. 9,10 Our 11 and more recent 12 attempts to detect an antiferromagnetic phase transition in silver, which motivated the present work, will be discussed elsewhere. A knowledge of x x is crucial in the interpretation of time-dependent phenomena associated with nuclear ordering, such as those observed in copper. l3 One of the striking consequences of Provotorov's theory is that mutual spin flips of unlike nuclei, the primary mechanism for CR, do not lead to thermal equilibrium because they do not affect the average Zeeman reservoir. 4,14 The only experimental ver...

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