Magnetic anisotropy in dysprosium single crystals

Two single crystals were grown by using the strain-anneal technique. Three rectangular parallelepiped samples were cut from these crystals with the long dimension directed along one of the hexagonal axes. These are designated as the \u3c1120\u3e a-axis, the \u3c1oTo\u3e b-axis, and the \u3c0001 \u3e c-axis

Thermal expansion of rare earth metals

A high temperature dilatometric investigation of the rare earth metals was undertaken as part of a broad program of study of these elements, the ultimate goal being better understanding of metals in general. The more immediate goal, in addition to determining the coefficients of expansion quantitatively, was to detect evidence of any crystalline transformations which may occur and particularly to cast some light on certain high temperature transitions already discovered in several of these metals. The rare earth metals included in this investigation were lanthanum, cerium, praseodymium, neodymium, gadolinium, terbium, dysprosium, erbium, and ytterbium

The ferromagnetic properties of the rare earth metals

The magnetic moment of gadolinium was measured in applied fields of 4,000-18,000 oersteds, and over the temperature range of 20.4°K to 320°K

The resistivity of lanthanum, cerium, praseodymium and neodymium at low temperatures

The electrical resistivity of lanthanum, cerium, praseodymium, and neodymium was measured between room temperature and approximately 2°K. The behavior was found to be affected by the method of preparation, the heat treatment, and the crystal structure of the samples, the latter bearing the greatest significance

Nernst-Ettingshausen effect in thin Pt and W films at low temperatures

As spin caloritronic measurements become increasingly common techniques for characterizing material properties, it is important to quantify potentially confounding effects. We report measurements of the Nernst-Ettingshausen response from room temperature to 5 K in thin film wires of Pt and W, metals commonly used as inverse spin Hall detectors in spin Seebeck characterization. Johnson-Nyquist noise thermometry is used to assess the temperature change of the metals with heater power at low temperatures, and the thermal path is analyzed via finite-element modeling. The Nernst-Ettingshausen response of W is found to be approximately temperature-independent, while the response of Pt increases at low temperatures. These results are discussed in the context of theoretical expectations and the possible role of magnetic impurities in Pt.Comment: 14 pages, 3 figures + supplementary material of 12 pages and 5 figure

Magnetic Order Beyond RKKY in the Classical Kondo Lattice

We study the Kondo lattice model of band electrons coupled to classical spins, in three dimensions, using a combination of variational calculation and Monte Carlo. We use the weak coupling `RKKY' window and the strong coupling regime as benchmarks, but focus on the physically relevant intermediate coupling regime. Even for modest electron-spin coupling the phase boundaries move away from the RKKY results, the non interacting Fermi surface no longer dictates magnetic order, and weak coupling `spiral' phases give way to collinear order. We use these results to revisit the classic problem of 4f magnetism and demonstrate how both electronic structure and coupling effects beyond RKKY control the magnetism in these materials.Comment: 6 pages, 4 figs. Improved figures, expanded captions. To appear in Europhys. Let

Spin Seebeck effect at low temperatures in the nominally paramagnetic insulating state of vanadium dioxide

The low temperature monoclinic, insulating phase of vanadium dioxide is ordinarily considered nonmagnetic, with dimerized vanadium atoms forming spin singlets, though paramagnetic response is seen at low temperatures. We find a nonlocal spin Seebeck signal in VO2 films that appears below 30 K and which increases with decreasing temperature. The spin Seebeck response has a non-hysteretic dependence on in-plane external magnetic field. This paramagnetic spin Seebeck response is discussed in terms of prior findings on paramagnetic spin Seebeck effects and expected magnetic excitations of the monoclinic ground state.Comment: 11 pages, 3 figures, + 11 pages and 10 figures of supplemental materia

The challenges of measuring spin Seebeck noise

Just as electronic shot noise results from the granularity of charge and the statistical variation in the arrival times of carriers in driven conductors, there are predictions for fundamental noise in magnon currents due to angular momentum being carried by discrete excitations. The advent of the inverse spin Hall effect as a transduction mechanism to convert spin current into charge current raises the prospect of experimental investigations of such magnon shot noise. Spin Seebeck effect measurements have demonstrated the electrical detection of thermally driven magnon currents and have been suggested as an avenue for accessing spin current fluctuations. We report measurements of spin Seebeck structures made from yttrium iron garnet on gadolinium gallium garnet. While these measurements do show an increase in measured noise in the presence of a magnetic field at low temperatures, the dependence on field orientation suggests an alternative origin for this signal. We describe theoretical predictions for the expected magnitude of magnon shot noise, highlighting ambiguities that exist. Analysis in terms of the sample geometry dependence of the known inverse spin Hall transduction of spin currents into charge currents implies that magnon shot noise detection through this approach is strongly suppressed. Implications for future attempts to measure magnon shot noise are discussed.Comment: 20 pages, 3 figures, + 7 pages/6 figures of supplementary materia