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The magnetic behavior of the low-dimensional phosphates ${(\mathrm{Sr},\mathrm{Ba})}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ and $\mathrm{Ba}\mathrm{Cu}{\mathrm{P}}_{2}{\mathrm{O}}_{7}$ was investigated by means of magnetic susceptibility and $^{31}\mathrm{P}$ nuclear magnetic resonance (NMR) measurements. We present here the NMR shift, the spin-lattice $(1∕{T}_{1})$, and spin-spin $(1∕{T}_{2})$ relaxation-rate data over a wide temperature range $0.02\phantom{\rule{0.3em}{0ex}}\mathrm{K}\ensuremath{\leqslant}T\ensuremath{\leqslant}300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature dependence of the NMR shift $K(T)$ is well described by the $S=1∕2$ Heisenberg antiferromagnetic chain model [D. C. Johnston, R. K. Kremer, M. Troyer, X. Wang, A. Kl\"umper, S. L. Bud'ko, A. F. Panchula, and P. C. Canfield, Phys. Rev. B 61, 9558 (2000)] with an intrachain exchange of $J∕{k}_{B}\ensuremath{\simeq}165$, 151, and $108\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in ${\mathrm{Sr}}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$, ${\mathrm{Ba}}_{2}\mathrm{Cu}{(\mathrm{P}{\mathrm{O}}_{4})}_{2}$, and $\mathrm{Ba}\mathrm{Cu}{\mathrm{P}}_{2}{\mathrm{O}}_{7}$, respectively. Deviations from Johnston's expression are seen for all these compounds in the $T$ dependence of $K(T)$ at low temperatures. $^{31}\mathrm{P}$ is located symmetrically between the Cu ions and fluctuations of the staggered susceptibility at $q=\ensuremath{\pi}∕a$ should be filtered out due to vanishing of the geometrical form factor. However, the qualitative temperature dependence of our $^{31}\mathrm{P}$ NMR $1∕{T}_{1}$ indicates that relaxation due to fluctuations around $q=\ensuremath{\pi}∕a$ (but $\ensuremath{\ne}\ensuremath{\pi}∕a$) have the same $T$ dependence as those at $q=\ensuremath{\pi}∕a$ and apparently dominate. Our measurements suggest the presence of magnetic ordering at $0.85\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $\mathrm{Ba}\mathrm{Cu}{\mathrm{P}}_{2}{\mathrm{O}}_{7}$ $(J∕{k}_{B}\ensuremath{\simeq}108\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and a clear indication of a phase transition (divergence) in $1∕{T}_{1}(T)$, $1∕{T}_{2}(T)$, and a change of the line shape is observed. This enables us to investigate the one-dimensional (1D) behavior over a wide temperature range. We find that $1∕{T}_{1}$ is nearly $T$ independent at low temperatures $(1\phantom{\rule{0.3em}{0ex}}\mathrm{K}\ensuremath{\leqslant}T\ensuremath{\leqslant}10\phantom{\rule{0.3em}{0ex}}\mathrm{K})$, which is theoretically expected for 1D chains when relaxation is dominated by fluctuations of the staggered susceptibility. At high temperatures, $1∕{T}_{1}$ varies nearly linearly with temperature, which accounts for contribution of the uniform susceptibility.

Crystal structure, magnetic susceptibility, and specific heat were measured in the normal cubic spinel compounds ${\mathrm{MnSc}}_{2}{\mathrm{S}}_{4}$ and ${\mathrm{FeSc}}_{2}{\mathrm{S}}_{4}$. Down to the lowest temperatures, both compounds remain cubic and reveal strong magnetic frustration. Specifically the Fe compound is characterized by a Curie-Weiss (CW) temperature ${\ensuremath{\Theta}}_{\mathrm{CW}}=\ensuremath{-}45\text{ }\text{ }\mathrm{K}$ and does not show any indications of order down to 50 mK. In addition, the Jahn-Teller ion ${\mathrm{Fe}}^{2+}$ is orbitally frustrated. Hence, ${\mathrm{FeSc}}_{2}{\mathrm{S}}_{4}$ belongs to the rare class of spin-orbital liquids. ${\mathrm{MnSc}}_{2}{\mathrm{S}}_{4}$ is a spin liquid for temperatures $Tg{T}_{N}\ensuremath{\approx}2\text{ }\text{ }\mathrm{K}$.

Measurements of magnetization M(T, H), heat capacity C(T), NMR lineshift K(T) and linewidth Δ(T), neutron scattering S(Q, ω, T) and broadband dielectric spectroscopy (ω, T) provide experimental evidence of the different orbital ground states in the cubic sulfur spinels under investigation. In all compounds, the tetrahedrally coordinated Jahn–Teller ions Fe2+ are characterized by a degeneracy of the orbital degrees of freedom. Particularly, we found a long-range orbital ordering in polycrystalline (PC) FeCr2S4, and a glassy freezing of the orbital degrees of freedom in FeCr2S4 (single crystals) (SCs). In contrast, FeSc2S4 belongs to the rare class of spin–orbital liquids, where quantum fluctuations accompanying the glassy freezing of the orbitals suppress long-range magnetic order.

Crystal structure, magnetic susceptibility, and specific heat were measured in the normal cubic spinel compounds MnSc2S4 and FeSc2S4. Down to the lowest temperatures, both compounds remain cubic and reveal strong magnetic frustration. Specifically the Fe compound is characterized by a Curie-Weiss (CW) temperature ThetaCW = -45 K and does not show any indications of order down to 50 mK. In addition, the Jahn-Teller ion Fe2+ is orbitally frustrated. Hence, FeSc2S4 belongs to the rare class of spin-orbital liquids. MnSc2S4 is a spin liquid for temperatures TTN approximately 2 K.

Heavy-fermion formation in transition metals and transition-metal oxides is reviewed and compared to observations in canonical f-derived heavy-fermion systems. The work focuses on the dynamic susceptibilities which reveal a characteristic temperature and frequency dependence and which can be unambiguously determined via nuclear magnetic resonance and electron-spin resonance measurements as well as via quasielastic neutron-scattering studies. Different routes to heavy-fermion behaviour are discussed, amongst them Kondo systems, frustrated magnets, and electronically correlated systems close to a metal-insulator transition. From a theoretical point of view, utilizing dynamical mean-field theory, we show that dynamic susceptibilities as calculated for the Hubbard model and for the periodic Anderson model look qualitatively rather similar. These different theoretical concepts describe an universal behaviour of the temperature dependent dynamic susceptibility.

We present susceptibility, microwave resistivity, NMR and heat-capacity results for Li1-xZnx(V1-yTiy)2O4 with 0 ? x ? 0.3 and 0 ? y ? 0.3. For all doping levels the susceptibility curves can be fitted with a Curie-Weiss law. The paramagnetic Curie-Weiss temperatures remain negative with an average value close to that of the pure compound Θ≈ - 36 K. Spin-glass anomalies are observed in the susceptibility, heat-capacity and NMR measurements for both type of dopants. From the temperature dependence of the spin-lattice relaxation rate we found critical-dynamic behavior in the Zn doped compounds at the freezing temperatures. For the Ti-doped samples two successive freezing transitions into disordered low-temperature states can be detected. The temperature dependence of the heat capacity for Zn-doped compounds does not resemble that of canonical spin glasses and only a small fraction of the total vanadium entropy is frozen at the spin-glass transitions. For pure LiV2O4 the spin-glass transition is completely suppressed. The temperature dependence of the heat capacity for LiV2O4 can be described using a nuclear Schottky contribution and the non-Fermi liquid model, appropriate for a system close to a spin-glass quantum critical point. Finally an ( x / y , T )-phase diagram for the low-doping regime is presented.

NMR, EPR, and bulk susceptibility measurements were performed in the perovskite-related layered compound ${\mathrm{SrNbO}}_{3.41}.$ We determined ${}^{93}\mathrm{Nb}$ NMR spectra, spin-spin relaxation rates ${1/T}_{2}$ and spin-lattice relaxation rates ${1/T}_{1}$ down to 600 mK. From the spin-lattice relaxation ${1/T}_{1}$ we identified an activated behavior ${1/T}_{1}\ensuremath{\propto}\mathrm{exp}(\ensuremath{-}{\ensuremath{\Delta}}_{\mathrm{NMR}}{/k}_{B}T)$ with a gap ${\ensuremath{\Delta}}_{\mathrm{NMR}}=6.5\mathrm{meV}$ for temperatures $Tg20\mathrm{K}.$ Below 20 K, the line width $\ensuremath{\Delta}H(T)$ from acceptor-EPR and ${}^{93}{(1/T}_{1})(T)$ both exhibit a temperature dependence propotional to $\mathrm{exp}[\ensuremath{-}{(T}_{0}{/T)}^{1/2}]$ which is indicative for a variable range hopping process. We discuss the possibility of charge-density-wave formation at low temperatures.

7Li NMR measurements were performed in the metallic spinel LiV2O4. The temperature dependence of the spin-lattice relaxation rate is documented in the temperature range 100 mK < T < 280 K. A comparison with the spin-glass behavior of Li1–xZnxV2O4 for small concentrations of x is given. For low temperatures T < 1 K we observe a maximum for the spin-lattice relaxation rate in LiV2O4. The frequency dependence of this maximum is indicative for a slowing down of spin fluctuations. The NMR results can be explained by a spin-liquid behavior and the opening of a spin gap of the order 1 K. PACS Nos.: 75.20Hr, 75.50Lk, 76.60Es, 76.60-k

7Li NMR measurements were performed in the metallic spinel LiV2O4. The temperature dependencies of the line width, the Knight shift and the spin-lattice relaxation rate were investigated in the temperature range 30 mK < T < 280 K. For temperatures T < 1 K we observe a spin-lattice relaxation rate which slows down exponentially. The NMR results can be explained by a spin-liquid behavior and the opening of a spin gap of the order 0.6 K.

We present bulk susceptibility and 31 P NMR measurements for BaCuP 2 O 7 . The data above 1 K are in good agreement with the S = 1 2 Heisenberg antiferromagnetic chain model with an intra-chain exchange constant J / k B = 108 K . Clear anomalies are observed at 0.85 K in the temperature dependence of the 31 P NMR shift, spin-lattice relaxation rate, and the spectra signifying the onset of some type of long-range order. The shape of the NMR spectra below 0.85 K suggest the occurrence of incommensurate order.

The quasi-ternary heavy-fermion systems Ce(Cu1−xNix)2Ge2 and CeCu2(Si1−yGey)2 are investigated by means of magnetic resonance. Starting with the common CeCu2Ge2 both systems exhibit an alloying-induced transition from antiferromagnetic order to a coherent Fermi-liquid behavior in CeNi2Ge2 and CeCu2Si2, respectively.