The Fe-57 Mossbauer effect of DyFe2Zn20 and YFe2Zn20 was studied at temperatures between 8 and 301 K, and at room temperature in the presence of an external magnetic field. The spectra of the two compounds appeared almost the same at temperatures above 77 K. Each spectrum exhibited a double peak, which is attributed to the electric field gradient (EFG) present at the Fe nuclei. However, the spectrum of DyFe2Zn20 at 8K exhibited a complicated shape, resulting from a magnetic hyperfine field and the EFG at the Fe nuclei. From the detailed analyses of the spectra, we concluded that Fe magnetic moments interact antiferromagnetically with Dy magnetic moments and that the Fe magnetic moments in DyFe2Zn20 at 8K are approximately 0.2 mu(B)/Fe.

The temperature dependence of quadrupole splitting for YbxFe4Sb12 deviates from the T-3/2 law because of the itinerant electron contribution to the electric field gradient (EFG). Each of the Fe-57 Mossbauer spectra of Yb0.89Fe4Sb12 is a double peak with similar asymmetries above and at 45 K; however, the asymmetry of the double peak varies with temperature below 45 K. The asymmetry variation in the temperature range from 45 to 13 K is explained by the increasing valence of the Yb ion in cages adjacent to cages with Yb deficiency, and the asymmetry in the spectra below 13 K is explained by the angle between the principal axis of the EFG tensor and the internal magnetic field.

The magnetization and specific heat of single-crystalline samples of filled-skutterudite compounds YbxFe4Sb12 were measured. Six single crystals with the filling ratio of Yb, x, from 0.875 to 0.910 were prepared. The weak ferromagnetism of YbxFe4Sb12 appearing at low temperatures was found to strongly correlate with x; with increasing x from 0.875 to 0.910, the transition temperature, T-C, decreases from 17 to 5 K and the weak-ferromagnetic moment, m(0), decreases from 0.066 to 0.005 mu(B)/Fe. From these trends, both T-C and m(0) were expected to reach zero at the critical concentration, x(c) = 0.93. In the temperature dependence of the specific heat, no anomaly at T-C was observed, reflecting that m(0) is extremely small compared with the effective Bohr magneton number. With the application of pressure, the T-C of the sample with x = 0.882 increases rapidly, with the ratio of dT(C)/dP = +5.27 K/GPa. This weak ferromagnetism of YbxFe4Sb12 originates from the itinerant 3d electrons of Fe in anions [Fe4Sb12].

Populations of spider mites were sampled from kudzu vine Pueraria lobata (Willd.) from 1997 to 1999 at two study sites in Ibaraki, central Japan. Of the five spider mite species sampled, Tetranychus pueraricola Ehara and Gotoh was the most abundant (accounting for 75.6-96.9% of mites) in each of the three years. The next most abundant species were T ludeni Zacher (0.8-19.0%), T. parakanzawai Ehara (1.1-9.7%) and T piercei McGregor (3.1%), but their density and species richness varied from year to year and from site to site. The populations peaked in June and/or September-October. Predators associated with spider mite populations were phytoseiid mites such as Amblyseius tsugawai Ehara, Phytoseius nipponicus Ehara and Neoseilus womersleyi (Schicha), Scolothrips takahashii Priesner, Oligota spp., Feltiella spp. and stigmaeid mites such as Agistemus exsertus Gonzalez and A. terminalis (Quayle), which were well synchronized with spider mite density Overwintered females began to appear and oviposit on some herbaceous weeds growing at the study sites in early April. Spider mites appeared on kudzu vine leaves in early May just after flushing. Most colonies (defined as areas surrounded with silky spider mite threads) had only one species but a small percentage had two or three species.

In a previous paper, the authors studied two samples of YbxFe4Sb12 (#1 and #2) by the Fe Mossbauer effect; it was found that the quadrupole splitting (QS 1⁄4 eqQ=2) for YbxFe4Sb12 (#1) at each temperature was slightly less than that for YbxFe4Sb12 (#2), thereby leading the authors to conjecture that the filling ratio x of Yb atoms in YbxFe4Sb12 (#2) was smaller than x in YbxFe4Sb12 (#1). However, in more recent papers, Ikeno et al. concluded that the ferromagnetic-transition temperature TC decreased with increasing x. From the relationship of x versus TC, the filling ratios in YbxFe4Sb12 (#1) and YbxFe4Sb12 (#2) are estimated at x 0:89 and x & 0:92, respectively. This indicates that x in YbxFe4Sb12 (#2) is larger than x in YbxFe4Sb12 (#1). In this paper, we explain the causation of the fact that QS increases with increasing x, and obtain the value of x in YbxFe4Sb12 (#2). The electric-field gradient eq at the Fe site is expressed as follows:

5歳齢，雌のキャバリア・キング・チャールズ・スパニエルに，眼囲，口囲，肘，踵，肉球，陰部周囲におよぶ角化性皮疹が生じた。発症に先行して，出産と食餌変更があった。病理組織学的検査で毛漏斗部におよぶ錯角化と著しい表皮肥厚を認め，一部に浮腫がみられた。真皮乳頭では多形核球や単核球の浸潤が観察された。血液検査，甲状腺ホルモン検査，血清アレルギー検査で特記すべき異常はみられなかった。以上より亜鉛反応性皮膚症と診断した。亜鉛製剤の内服後角化の改善を認めたが痒みは持続し，前医にて単独投与では奏効しなかったプレドニゾロンの内服を併用したところ皮疹は消退した。寛解後亜鉛補充療法もステロイドも必要としなかった。自験例が本症の好発犬種ではないことから，病因として食餌による一時的な亜鉛吸収傷害が予想された。

We prepared two YbFe4Sb12 samples (#1 and #2) and a LaFe4Sb12 sample. Mossbauer and magnetization measurements were performed on the samples at various temperatures and in applied magnetic fields. The experimental results indicate that #1 is in a weakly ferromagnetic state below 13 K, while #2 is in an itinerant paramagnetic state even at 2 K, and that quadrupole splitting for #1 at each temperature is slightly less than that for #2. Therefore, we conclude that YbFe4Sb12 is an intermediate material between a nearly ferromagnetic material and a weakly ferromagnetic material.

To explain the results of magnetization measurements and Mössbauer measurements on interacting iron oxide nanocrystals which have been produced by leaving iron nanoparticles in air of 1atm for 10 years, we propose the following model. Several tens of the oxide nanocrystals randomly cohere to form a cluster. As a result, we assume that each nanocrystal within a cluster has random unidirectional magnetic anisotropy, and that the clusters are weakly interacting each other at random. The super-spin-glass model is used for analyzing the random interaction among the clusters.

The Mossbauer effect in CeFe2Al8 was measured at temperatures from 8 to 306 K and in applied magnetic fields up to 1.05 T. For comparison, the Mossbauer effect in LaFe2Al8 was also measured at temperatures from 78 to 300 K and in applied magnetic fields up to 1.05 T. Each Mossbauer spectrum of CeFe2Al8 and LaFe2Al8 consists of two doublers with almost the same area, indicating that both the compounds have no magnetic order in those temperature ranges. Moreover, careful consideration to the experimental results (i.e. the magnetic susceptibility and the Mossbauer spectra) suggests that Fe atoms on both the sites (1 and 2) of CeFe2Al8 and LaFe2Al8 do not have a local magnetic moment, and the comparison of the experimental results of CeFe2Al8 with those of LaFe2Al8 suggests that each Ce atom in CeFe2Al8 is in an intermediate valence state between Ce3+ and Ce4+. (C) 2000 Elsevier Science B.V. All rights reserved.

Néel temperature (Tm N of α-Fe2SiO4 (fayalite) was measured as a function of pressure by means of Mössbauer spectroscopy in the pressure range 0–16 Gpa. High pressure was generated using a clamp-type miniature diamond anvil cell which was inserted into a cryostat. The Néel temperature increased linearly with increasing pressure at a rate of dT N /dp=2.2±0.2 K/GPa. The result is discussed on the basis of the model proposed for the magnetic structure of fayalite by Santoro et al. (1966). The observed dT N /dp suggests that the superexchange interactions vary as the −10/3 power of the volume while the volume dependence of the direct exchange interactions is positive and small.