| 1. |
- Grechnev, G. E., et al.
(författare)
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Anisotropy of magnetic properties of Fe1+y Te
- 2014
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:43, s. 436003-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of Fe1+y Te single crystals (y similar or equal to 0.1 divided by 0.18) were studied at temperatures 4.2 divided by 300 K. At an ambient pressure, with decreasing temperature a drastic drop in chi(T) was confirmed at T similar or equal to 60 divided by 65 K, which appears to be closely related to the antiferromagnetic (AFM) ordering. It is found that the magnitudes of the anisotropy of magnetic susceptibility Delta chi. in the AFM phase are close in the studied samples, whereas the sign of the anisotropy apparently depends on the small variations of the excess iron y in Fe1+y Te samples. The performed DFT calculations of the electronic structure and magnetic properties for the stoichiometric FeTe compound indicate the presence of frustrated AFM ground states. There are very close energies and magnetic moments for the double stripe configurations, with the AFM axes oriented either on the basal plane or along the [0 0 1] direction. Presumably, both these configurations can be realized in Fe1+y Te single crystals, depending on the variations of the excess iron. This can provide different signs of magnetic anisotropy in the AFM phase, presently observed in the Fe1+y Te samples. For these types of AFM configuration, the calculations for the FeTe values of Delta chi are consistent with our experimental data.
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| 2. |
- Noël, Maxime, et al.
(författare)
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Effects of non-hydrostatic pressure on electrical resistance of bundled single-wall carbon nanotubes
- 2013
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Ingår i: 7th EEIGM International Conference on Advanced Materials Research. - : IOP Publishing Ltd.
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Konferensbidrag (refereegranskat)abstract
- Recent studies have shown that single wall carbon nanotubes (SWCNT) exhibit a sequence of phase transitions and demonstrate a high structural stability up to 35 GPa of quasi-hydrostatic pressure [1] beyond which an irreversible structural transformation occurs. Here we report on the study of electrical resistance of SWCNTs at pressures up to 34 GPa in the temperature range of 293 – 395 K. In the pressure range 10–25 GPathe rate of resistance change decreases considerably. We associate such behavior of the resistance with a structural modification of the SWCNTs or/and change of the conductivity character at high pressure. Raman spectra of the samples recovered after 30 GPa exhibit a large increase of defect concentration in the CNTs. Isobaric temperature dependences of the CNT resistance R(T) measured in the temperature range 300–400 K reveal some changes with pressure whereas the semiconducting character of the R(T) remains unaltered.
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| 3. |
- Noël, Maxime, et al.
(författare)
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Electrical transport in bundled single-wall carbon nanotubes under high pressure
- 2013
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Konferensbidrag (refereegranskat)abstract
- According to recent experimental data single wall carbon nanotubes (SWCNT) exhibit a sequence of phase transitions and demonstrate a high structural stability up to 35 GPa of non-hydrostatic pressure beyond which an irreversible transformation occurs. Here we report a study of electrical transport in SWCNTs at pressures up to 45 GPa in the temperature range of 300 - 400K. High pressure was generated in diamond anvil cell. The anvils are made of electrically conducting "carbonado"-type synthetic diamond. In the pressure range 10-25 GPa the CNT electrical resistance decreases considerably, whereas above 25 GPa it remains essentially unchanged. Such behaviour of the resistance can be connected to a structural modification of the SWCNTs accompanied by change of the conductivity character at high pressure. Raman spectra of the samples recovered after 30 GPa exhibit a large increase of D/G band intensity ratio. The Radial Breathing Mode part of the spectra remains essentially unaltered which testifies for structural integrity of the nanotubes after exposure to high non-hydrostatic pressure and lack of covalent interlinking between the tubes. Pressure dependences of resistance, activation energy for conductivity and charge carriers mobility were determined and discussed.
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| 4. |
- Svensson, Gunnar, 1960-, et al.
(författare)
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Synthesis and characterisation of the novel double perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu
- 2012
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Ingår i: Materials Research Bulletin. - : Elsevier BV. - 0025-5408 .- 1873-4227. ; 47:9, s. 2449-2454
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Tidskriftsartikel (refereegranskat)abstract
- The novel perovskites La2CrB2/3Nb1/3O6, B = Mg, Ni, and Cu have been synthesised at 1350 degrees C in air via the citrate route. Rietveld refinements using neutron powder diffraction (NPD) data showed that the compounds adopt the GdFeO3 type structure with space group Pbnm, and unit cell parameters a approximate to b approximate to root 2 x a(p) and c approximate to 2 x a(p), where a(p) approximate to 3.8 angstrom. Selected area electron diffraction (SAED) of B = Ni and Cu samples confirmed space group Pbnm. However, distinct reflections forbidden in Pbnm symmetry, but allowed in the monoclinic sub-group P2(1)/n and unit cell parameters a approximate to b approximate to root 2 x a(p) and c approximate to 2 x a(p), beta approximate to 90 degrees were present in SAED patterns of B = Mg sample. This indicates an ordering of the B-cations within the crystal structure of La2CrMg2/3Nb1/3O6. High-resolution electron microscopy (HREM) study indicating uniform, without formation of clusters, ordering of B-cations in the crystallites of La2CrMg2/3Nb1/3O6. Magnetic susceptibility measurements show that the compounds are antiferromagnetic (with some glass or spin clustering effects due to additional ferromagnetic interactions between the B-cations) with T-N for La2CrB2/3Nb1/3O6, B = Mg, Ni, Cu being 90, 125 and 140K, respectively.
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