Specific heat measurements down to 120mK have been performed on a quasi-one-dimensional S = 1/2 spin-gapped system (CH3)2NH2CuCl3 in a magnetic field up to 8 T. This compound has a characteristic magnetization curve which shows a gapless ground state and a plateau at 1/2 of the saturation value. We have observed a spontaneous antiferromagnetic ordering and a field-induced one below and above the 1/2 plateau field range, respectively. The field versus temperature phase diagram is quite unusual and completely different from those of the other quantum spin systems investigated so far. In the plateau field range, a double-structure in the specific heat is observed, reflecting the coexistence of ferromagnetic and antiferromagnetic excitations. These behaviors are discussed on the basis of a recently proposed novel quantum spin chain model consisting of weakly coupled ferromagnetic and antiferromagnetic dimers.KEYWORDS: specific heat, spin-gapped system, field-induced magnetic orderingIn recent years, field-induced quantum phenomena in spin-gapped systems, such as field-induced magnetic orderings (FIMO) and plateaux in the magnetization curve M (H), have been brought to attention as one of the hottest topics in condensed matter physics. Spin-gapped systems are magnetically inactive and have energy gaps in the energy spectrum at zero or finite fields because of forming antiferromagnetic singlet dimers, but magnetic excited states exist above these energy gaps. Thus, by application of an external field, field-induced magnetic states are realized due to the Zeeman energy gain above certain critical fields. In these magnetic states, spin components perpendicular to the field direction show threedimensional (3D) long-range orderings triggered by interchain and/or interdimer interactions at low enough temperatures, and the resultant ordered phase ususally has the reentrant H-T phase boundary with a parabolic shape between two critical fields. This kind of the FIMO was firstly investigated in an alternating chain system Cu(NO 3 ) 2 ·2.5H 2 O 1) and explained by Tachiki and Yamada based on the mean-field theory.2) Recently, Nikuni et al. have discussed this kind of the FIMO on the basis of a Bose-Einstein condensation of excited magnons, 3) and then FIMO observed in spin-gapped compounds have been analyzed within this framework. 4-6)Our model substance in this study is an S = 1/2 quasi one-dimensional (1D) spin-gapped system (CH 3 ) 2 NH 2 CuCl 3 (DMACuCl 3 ). This compound has a unique magnetic chain forming an alternating chain of antiferromagnetic (S = 0) and ferromagnetic (S = 1) dimers coupled by an intervening weak interaction, as proposed recently from the low-T x-ray diffraction and magnetization measurements.7, 8) In this system, there are three kinds of nearest-neighbor intrachain interac- * E-mail address: yasuotap@mbox.nc.kyushu-u.ac.jp tions, J AF , J F and J, in a sequence of -J -J AF -J -J F -J -, where J AF and J F are antiferromagnetic (AF) and ferromagnetic (F) interactions responsible to the AF and F dimers...

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We investigated the effect of Si wet etching on the vertical step at wafer edge. We found that the concave-convex shape appeared at the wafer edge after Si etching by the Atomic Force Microscopy analysis. From the liquid simulation and the detailed evaluation of Si etching rate, we revealed that the concave-convex shape was formed by the distribution of the fluid velocity at the wafer edge.

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