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The environment of Gd 3+ (4f 7 , S = 7/2) ions in single crystals of Ca 1-x Gd x B 6 (0.0001≤x≤0.01) is studied by electron spin resonance (ESR). The spectra for x≤0.001 show a split spectrum due to cubic crystal field effects (CFE). The line shape of each fine structure line is Lorentzian, indicating an insulating environment for the Gd 3+ ions. For 0.003≤x≤0.01, the spectra show a single resonance (g 1.992(4), ΔH 1/2 60 Oe) with no CFE and Dysonian line shape indicating metallic environment for the Gd. 3+ ions. For intermediate concentrations, a coexistence of spectra corresponding to insulating and metallic regions is observed. Most of the measured samples show the weak ferromagnetism (WF) as reported for Ca 0.995 La 0.005 B 6 , but, surprisingly, this WF has no effect in our ESR spectra either for metallic or insulating environments. This result suggests that the WF in these systems might be isolated in clusters (defect-rich regions) and its relationship with metallicity is nontrivial.

We present transport and thermodynamic measurements as a function of temperature (0.1{endash}300 K), pressure (1 bar{endash}16 kbars), and magnetic field (0{endash}600 kOe) on YbInNi{sub 4}. Ferromagnetism arises near 3 K out of a state with enhanced electronic specific-heat coefficient. Resistivity, specific-heat, and magnetization measurements imply that the ground state of YbInNi{sub 4} is a crystal-field doublet, whereas earlier neutron-scattering results suggest a ground-state quartet. We also compare YbInNi{sub 4} to YbInCu{sub 4} and intermediate alloys. {copyright} {ital 1998} {ital The American Physical Society}

The pressure induced quantum phase transition of the weakly itinerant ferromagnet MnSi is studied using zero-field $^{29}Si$ NMR spectroscopy and relaxation. Below $P^*\approx 1.2GPa$, the intensity of the signal and the nuclear spin-lattice relaxation is independent of pressure, even though the amplitude of the magnetization drops by 20% from the ambient pressure amplitude. For $P>P^*$, the decreasing intensity within the experimentally detectable bandwidth signals the onset of an inhomogeneous phase that persists to the highest pressure measured, $P\ge 1.75GPa$, which is well beyond the known critical pressure $P_c=1.46GPa$. Implications for the non-Fermi Liquid behavior observed for $P>P_c$ are discussed., 4 pages, 4 figures

Neutron-diffraction measurements in ${\mathrm{L}\mathrm{a}\mathrm{C}\mathrm{r}\mathrm{S}\mathrm{b}}_{3}$ show a coexistence of ferromagnetic and antiferromagnetic sublattices below ${T}_{C}=126\text{ }\text{ }\mathrm{K}$, with ordered moments of 1.65(4) and $0.49(4){\ensuremath{\mu}}_{B}/\mathrm{\text{formula unit}}$, respectively ($T=10\text{ }\text{ }\mathrm{K}$), and a spin-reorientation transition at $\ensuremath{\approx}95\text{ }\text{ }\mathrm{K}$. No clear peak or step was observed in the specific heat at ${T}_{C}$. Coexisting localized and itinerant spins are suggested.

We report measurements of anisotropy in magnetic susceptibility, magnetization, and electrical resistivity using single crystals of $\mathrm{La}T{\mathrm{Sb}}_{3}$ $(T=\mathrm{Cr},\mathrm{V}).$ $\mathrm{La}T{\mathrm{Sb}}_{3}$ is a quasi-two-dimensional system with an orthorhombic crystal structure (space group $Pbcm),$ possessing a rich phase diagram with a ferromagnetic transition at ${T}_{C}=132 \mathrm{K}$ due to the ordering of the Cr ions. In order to investigate $\mathrm{La}T{\mathrm{Sb}}_{3},$ magnetic susceptibility and magnetization for fields up to 55 kG and in the temperature range of 2--350 K have been measured with the field aligned to the three principle axes. The electrical resistivity of ${\mathrm{LaCrSb}}_{3}$ has been measured for currents parallel to the a, b, and c axes in the temperature range 5--295 K, as well as magnetoresistances at 20 k and 60 kG along the b axis. Isostructural ${\mathrm{LaVSb}}_{3}$ is found have no transitions in either the magnetization or the resistivity; therefore, it is presented as a nonmagnetic counterpart. Just below ${T}_{C},$ the easy axis is found to be within the $b\ensuremath{-}c$ plane in the direction of the magnetic field. As the system is further cooled, there is a crossover from quasi-two-dimensional (2D) to 3D anisotropy below a characteristic temperature ${T}^{*},$ and the easy axis of magnetization becomes oriented along the b axis. Furthermore, it is found that ${T}^{*}$ decreases linearly as the magnetic field is increased, and is suppressed with a field $Hg3.7 \mathrm{kG}.$ A high-temperature antiferromagnetic transition is found at ${T}_{N}=98 \mathrm{K}.$ The value of ${T}_{N}$ is found to be independent of the applied magnetic field up to $H=0.25 \mathrm{kG},$ at which point this antiferromagnetic phase is suppressed.

Electron spin resonance (ESR) and magnetic-susceptibility experiments in the rare-earth-doped ({ital R}=Nd, Er, and Yb) cubic semiconducting YBiPt allow estimates of the fourth (A{sub 4}) and sixth (A{sub 6}) order crystal-field parameters for this compound. It is found that these parameters are of the same order for all the {ital R} studied. On the other hand, no crystal-field effects were found for the Gd{sup 3+} doped single-crystal system. Consistent with the small gap semiconducting character of the YBiPt intermetallic compound, a Dysonian ESR line shape with no {ital g} shift and Korringa broadening was observed. {copyright} {ital 1999} {ital The American Physical Society}

The magnetic properties of the ground state of a low-density free-electron gas in three dimensions have been the subject of theoretical speculation and controversy for seven decades. Not only is this a difficult theoretical problem to solve, it is also a problem which has not hitherto been directly addressed experimentally. Here we report measurements on electron-doped calcium hexaboride (CaB6) which, we argue, show that-at a density of 7× 1019 electrons cm-3-the ground state is ferromagnetically polarized with a saturation moment of 0.07 µB per electron. Surprisingly, the magnetic ordering temperature of this itinerant ferromagnet is 600 K, of the order of the Fermi temperature of the electron gas.