Itinerant-Electron Magnet of the Pyrochlore Lattice: Indium-Doped YMn2Zn20

We report on a ternary intermetallic compound, "YMn2Zn20", comprising a pyrochlore lattice made of Mn atoms. A series of In-doped single crystals undergo no magnetic long-range order down to 0.4 K, in spite of the fact that the Mn atom carries a local magnetic moment at high temperatures, showing Curie-Weiss magnetism. However, In-rich crystals exhibit spin-glass transitions at approximately 10 K due to a disorder arising from the substitution, while, with decreasing In content, the spin-glass transition temperature is reduced to 1 K. Then, heat capacity divided by temperature approaches a large value of 280 mJ K-2 mol-1, suggesting a significantly large mass enhancement for conduction electrons. This heavy-fermion-like behavior is not induced by the Kondo effect as in ordinary f-electron compounds, but by an alternative mechanism related to the geometrical frustration on the pyrochlore lattice, as in (Y,Sc)Mn2 and LiV2O4, which may allow spin entropy to survive down to low temperatures and to couple with conduction electrons.Comment: 5 pages, 4 figures, J. Phys. Soc. Jpn., in pres

Variation of the magnetic ordering in GdT2_2Zn20_{20} (T= Fe, Ru, Os, Co, Rh and Ir) and its correlation with the electronic structure of isostructural YT2_2Zn20_{20}

Magnetization, resistivity and specific heat measurements were performed on the solution-grown, single crystals of six GdT$_2$Zn$_{20}$ (T = Fe, Ru, Os, Co, Rh and Ir) compounds, as well as their Y analogues. For the Gd compounds, the Fe column members manifest a ferromagnetic (FM) ground state (with an enhanced Curie temperature, $T_{\mathrm{C}}$, for T = Fe and Ru), whereas the Co column members manifest an antiferromagnetic (AFM) ground state. Thermodynamic measurements on the YT$_2$Zn$_{20}$ revealed that the enhanced $T_{\mathrm{C}}$ for GdFe$_2$Zn$_{20}$ and GdRu$_2$Zn$_{20}$ can be understood within the framework of Heisenberg moments embedded in a nearly ferromagnetic Fermi liquid. Furthermore, electronic structure calculations indicate that this significant enhancement is due to large, close to the Stoner FM criterion, transition metal partial density of states at Fermi level, whereas the change of FM to AFM ordering is associated with filling of electronic states with two additional electrons per formula unit. The degree of this sensitivity is addressed by the studies of the pseudo-ternary compounds Gd(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ and Y(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ which clearly reveal the effect of 3d band filling on their magnetic properties.Comment: 32 pages, 28 figure

Unusual Field-Insensitive Phase Transition and Kondo Behavior in SmTi2_2Al20_{20}

Magnetization, electrical resistivity and specific heat measurements were performed on high-quality single crystalline SmTi$_2$Al$_{20}$ (residual resistivity ratio $\sim$ 40) grown by Al self-flux method. A Kondo-like $\log T$ dependence in the resistivity is observed below 50 K. We discovered a field-insensitive phase transition at $T_{x}$ = 6.5 K and a field-insensitive heavy fermion behavior with the electronic specific heat coefficient $\gamma$ = 150 mJ/(K$^{2}$ mol). Specific heat analysis reveals that the ground state is a $\Gamma_{8}$ quartet state and the Sm magnetic dipole moment $m_{{\rm Sm}}$ ($\sim 0.5 \mu_{{\rm B}}$ at $T \simeq$ 0) orders below $T_{x}$ in spite of the field-insensitive behavior. Possible reasons for the field insensitiveness will be discussed.Comment: 4 pages, 3 figures, to be published in J. Phys. Soc. Jpn. 80 (2011

Mechanisms of wafer sawing and impact on wafer properties

Silicon wafer wire-sawing experiments were realized with different sets of sawing parameters, and the thickness, roughness, and cracks depth of the wafers were measured. The results are discussed in relation to assumptions underlying the rolling-indenting model, which describes the process. It was also found that the silicon surface at the bottom of the sawing groove is different from the wafer surface, implying different sawing conditions in the two positions. Furthermore, the measured parameters were found to vary along the wire direction, between the entrance of the wire in the ingot and its exit. Based on these observations, some improvements for the wire-sawing model are discussed. Copyright (C) 2010 John Wiley & Sons, Ltd

Influence of abrasive concentration on the qualiy of wire-sawn silicon wafers

The sawing parameters have an impact on the depth of the defects in the wafers, and hence on their mechanical strength. However, as sawing is a highly complex system, the wafering industry is still relying on a “trial and error” approach to improve the sawing parameters. In this contribution, the effects of the abrasive concentration are studied with the help of the “rolling-indenting model”, the model most commonly used to describe the sawing process. From roughness and cracks depth measurement correlated with flexure tests, we show that using a lower silicon carbide concentration in the slurry decreases the depth of the defects as well as the roughness and results in a higher breakage strength of the wafers

Effects of edge defects induced by multi-wire sawing on the wafer strength

The focus of the photovoltaic industry is a continuous reduction of the cost of solar energy. Lowering the wafer thickness during the processing by means of multi-wire slurry saw technology is one of the key issue to reduce these costs. However, reducing the wafer thickness without increasing the wafer strength leads to a larger breakage rate during the subsequent fabrication steps. Hence, recent studies have been carried out to enhance the sawing process by minimizing the sub-surface defects. Nevertheless, little efforts have been made to determine at which stage in the wafering process, the most dangerous defects are created for solar cells processing. Are they made during the shaping of the silicon bricks from cast ingots, or during the slicing operation into wafers, or else? State of the art consists in polishing the bricks prior to wafering by multi-wire slurry saw. The goal of this paper is to bring some insights on the importance of the edge defects on the wafer strength. Results using various methods such as roughness measurement, wafer strength measurement with the 4-lines bending tests and finite elements calculations are presented. The main conclusion of this study is that the defects made during the shaping of the bricks prior to wafering can be of high importance with respect to wafer strength