Temperature Dependence Of NMR Frequency Research Articles

Proton NMR Study of Pyrochlore-Like Atacamite Mn2Cl(OH)3

The proton NMR spectrum of Mn 2 Cl(OH) 3 with zero applied field has rather sharp peaks, and a glassy property is not observed. The temperature dependence of NMR frequency shows that antiferromagnetic transition occurs at T N1 (=3.4 K), and that no anomaly appears at T N2 (=2.7 K). However, the change in frequency is considerably larger than the normal change caused by thermal fluctuation. The magnetic structure of Mn 2 Cl(OH) 3 determined by comparison with the observed proton NMR spectrum and the numerical calculated ones of various magnetic models shows that magnetic moments do not order in an “all-in all-out” orientation relative to the body center like antiferromagnetic pyrochlore, and not parallel to the local crystal field. The coexistence of antiferromagnetic and spin-glass moments does not reproduce the observed NMR spectrum. Our result suggests that the magnetic structure of atacamite Mn 2 Cl(OH) 3 is antiferromagnetic, but different from that of pyrochlore, although it is similar to the crystal...

Phase Transition of Superfluid 3He in Aerogel

We have studied phase transition of superfluid 3He in 97.5% porosity aerogel by NMR method. Above 1.0 MPa, superfluid phase transition has been observed. The transition temperature Tca is strongly suppressed from its bulk value. The Pressure-Temperature diagram suggests that superfluid phase will not appear below near 0.8 MPa. The A-B phase transition has been observed above 1.3 MPa, below which a state of superfluid phases remains to be identified. The temperature dependence of NMR frequency shifts Δf in the A-like and the B-like phases are almost linear at pressures below 2.4 MPa. We obtained the differential coefficient of NMR frequency shifts ∂(Δf)/∂(T/Tca) at 0.9Tca as a function of pressure, and it suggests that superfluid phase will not appear below near 0.8 MPa which is the same pressure estimated by P-T diagram.

SQUID application to NMR at zero external magnetic field

We have found NMR signals at zero external magnetic field using superconducting quantum interference device (SQUID). A large peak Cu-NMR signal in Cu(HCOO) 2·2H 2O is observed around 250 MHz at 230 mK. The temperature dependence of NMR frequency has been studied.

Spontaneous magnetization from NMR measurements and critical exponents in nickel

Nuclear magnetic resonance of Ni61 has been studied in pure nickel metal (of natural isotope composition) in the vicinity of the Curie point. The temperature dependence of NMR frequency has been measured up to 0·96Tc. Determination ofTc was aided by initial susceptibility measurements. The analysis of these results yields β=0·336±0·002 for the critical exponent describing the decrease of spontaneous magnetization to zero atTc. This value ofβ is in excellent agreement with the corresponding values obtained from NMR experiments in ferromagnetic EuS and antiferromagnetic MnF2, it differs, however, from the values obtained for nickel by other methods. In a general discussion of this problem which uses the theoretical relations between various critical exponents the earlier data, in particular those of Weiss and Forrer, are reexamined.