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BackgroundMulti-walled carbon nanotubes (MWCNTs) constitute one of the most promising types of nanomaterials in industry today. With their increasing use, the potential toxicity and carcinogenicity of MWCNT needs to be evaluated in bioassay studies using rodents. Since humans are mainly exposed to MWCNT by inhalation, we performed a 104-week carcinogenicity study using whole-body inhalation exposure chambers with a fibrous straight type of MWCNT at concentrations of 0, 0.02, 0.2, and 2 mg/m3 using male and female F344 rats.ResultsLung carcinomas, mainly bronchiolo-alveolar carcinoma, and combined carcinomas and adenomas were significantly increased in males exposed to 0.2 and 2 mg/m3 MWNT-7 and in females exposed to 2 mg/m3 MWNT-7 compared to the clean air control group. However, no development of pleural mesothelioma was observed. Concentration-dependent toxic effects in the lung such as epithelial hyperplasia, granulomatous change, localized fibrosis, and alteration in BALF parameters were found in MWNT-7 treatment groups of both sexes. There were no MWNT-7-specific macroscopic findings in the other organs, including the pleura and peritoneum. Absolute and relative lung weights were significantly elevated in male rats exposed to 0.2 and 2 mg/m3 MWNT-7 and in all exposed female groups. The lung burdens of MWNT-7 were clearly increased in a concentration-dependent as well as a duration-dependent manner.ConclusionThere is clear evidence that MWNT-7 is carcinogenic to the lungs of male and female F344 rats, however no plural mesothelioma was observed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-016-0164-2) contains supplementary material, which is available to authorized users.

R 2 Ti 2 O 7 (R = Y and various rare earth elements) has pyrochlore type structure, which consists of two kinds of three-dimensional networks individually formed by the corner-sharing R 4 -and Ti 4 -tetrahedra, respectively. Due to this structural characteristic, magnetic moments at the R sites are expected to be frustrated, if their nearest neighbor interaction is antiferromagnetic.For R = Tb, the value of Weiss temperature w is À19 K, indicating the Tb 3þ moments have antiferromagnetic nearest neighbor interaction and the system does not exhibit clear evidence for magnetic ordering. Previously, we investigated both the dynamical and static magnetic properties of Tb 2 Ti 2 O 7 by means of neutron scattering on a single crystal. 1-3) Based on results of measurements of the specific heat C and ac magnetic susceptibility , low temperature state of Tb 2 Ti 2 O 7 was discussed in ref. 4, too.The frustration is also expected even for the system with the ferromagnetic nearest neighbor interaction, if the moments have strong uniaxial anisotropy, where each moment lies along the local principal axis corresponding to the line which connects the site with the center of gravity of the tetrahedron. (There are four principal axes along [111] and other crystallographically equivalent directions.) Such the situation can be found in R 2 Ti 2 O 7 with R = Dy 5) and Ho, 6) which are called ''spin ice''.For Yb 2 Ti 2 O 7 , w is equal to be $0:53 K as shown in the inset of Fig. 1, indicating the nearest neighbor interaction between the Yb 3þ moments is ferromagnetic. The electronic ground state of Yb 3þ ion was reported to be a Kramers doublet with relatively small planar anisotropy, g ? ¼ 4:27 and g k ¼ 1:70, where g ? and g k are the g-values perpendicular to and along the local principal axis, respectively. 7) Sengupta et al. reported that the system has uniaxial anisotropy, g ? ¼ 0 and g k ¼ 3:4. 8) A sharp peak of C-T curve was reported at 0.24 K, indicating the existence of the phase transition. 9) However, Hodges et al. did not observe magnetic reflection except the small angle diffuse scattring. 7) In order to identify the specific heat anomaly at 0.24 K, we have carried out neutron diffraction and other magnetic measurements on a single crystal of Yb 2 Ti 2 O 7 down to 0.03 K by using dilution refrigerator. Here, we report that the system exhibits ferromagnetic transition at T C ¼ 0:24 K. We also discuss the low temperature behavior of the moments.A single crystal of Yb 2 Ti 2 O 7 was grown by a floating zone (FZ) method. The magnetization M was measured by using a SQUID magnetometer. The method of the ac magnetic susceptibility is described in ref. 4. Neutron measurements were carried out by using the triple axis spectrometer HQR (T1-1) installed at the thermal guide of JRR-3 of JAERI in Tokai. The crystal was oriented with [hh0] and [00l] axes in the scattering plane. Figure 1 shows the M-H curves of Yb 2 Ti 2 O 7 obtained at 5 K with the magnetic fields along [001], [110] and [111], where the anisotropy of the curves is ...

We studied the magnetic properties in a non-magnetic heavy-fermion compound CeIrIn 5 and an antiferromagnetic compound CeRhIn 5 with the tetragonal structure. High-field magnetization of CeIrIn 5 shows a weak metamagnetic transition around 420 kOe for the field along the [001] direction, while the magnetization gradually increases up to 500 kOe for [110]. On the other hand, we observed a two-step metamagnetic transition for the field perpendicular to [001] at 20 and 500 kOe in CeRhIn 5 . The magnetization is of the x-y type. The former transition indicates a 1/ cos θ dependence, where the θ means a tilted angle of the field direction from the (001) plane. From the magnetic susceptibility and high-field magnetization measurements, we formed a magnetic phase diagram in CeRhIn 5 . The temperature dependences of the magnetic susceptibility and thermal expansion coefficient of both compounds were analyzed on the basis of the crystalline electric field model.

Neutron scattering experiments have been carried out on the heavy fermion antiferromagnetic (AFM) superconductor CePt 3 Si with T N = 2.2 K and T SC = 0.75 K. We observed clear AFM Bragg reflections with Q 0 = (001/2) below and above T SC , indicating microscopic coexistence of AFM order and heavy fermion superconductivity. The AFM structure, of two interleaved ferromagnetic sublattices of local Ce 4f moments, has inversion symmetry under simultaneous space-time reversal. However, hybridization with Pt and Si breaks this degeneracy and a combination of these two competing effects may be relevant to an understanding of the simultaneous occurrence of superconductivity and AFM order. The observed magnetic moment 0.16(1) µ B /Ce is strongly reduced from the Curie-Weiss effective moment 2.54 µ B /Ce. Clear crystal field excitations at 1 and 24 meV were observed. The magnetic susceptibility can be well explained in a level scheme assuming the 7 ground state, 6 and 7 first and second excited states, respectively.

We present the recent advances in Ce-based heavy fermion superconductivity. Heavy fermions are formed by the competition between the Ruderman-Kittel-Kasuya-Yosida interaction and the Kondo effect. The application of pressure is useful for controlling the electronic states in antiferromagnets such as CeRh 2 Si 2 , Ce 2 Ni 3 Ge 5 , CeIn 3 , CeRhIn 5 , and CeIrSi 3 . For these compounds, the Néel temperature T N decreases with increasing pressure and reaches zero at the quantum critical pressure P c . Superconductivity appears around P c . In CeRu 2 , CeCoIn 5 , and CePt 3 Si, superconductivity is realized at ambient pressure. For these pressure-induced and ambient-pressure superconductors, we clarified their unconventional characteristics of superconductivity, the close relationship between superconductivity and the dimensionality of the electronic states, and a new aspect of superconductivity in the noncentrosymmetric crystal structure, together with its Fermi surface instability at P c .

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