40 research outputs found
Low-temperature giant coercivity in CoGaGe (=2.4 to 3.2)
The observation of giant coercivity exceeding 20 kOe at low temperatures in
several transition-metal-based compounds has attracted significant attention
from a fundamental perspective. This research is also relevant to developing
rare-earth-free permanent magnets, wherein cobalt is one of the primary
elements used. To facilitate easy fabrication, rare-earth-free and Co-based
inorganic bulk magnets that exhibit giant coercivity are highly demanded but
rarely reported. Herein, we report the observation of low-temperature giant
coercivity in polycrystalline metallic CoGaGe (=2.4
to 3.2) with the hexagonal FeGe-type structure composed of Kagome
and triangular lattices. As the Ge content decreases from 3.2, the magnetic
ground state changes from ferrimagnetism to ferromagnetism at =2.6. In the
ferrimagnetic state, we observed a signature of spin frustration arising from
the Kagome and/or triangular lattices of Co atoms. The ferromagnetic ordering
temperatures for the =2.6 and 2.4 samples are 46 K and 60 K, respectively.
The coercive fields rapidly increase upon cooling and reach values of 26 kOe
and 44 kOe in the =2.6 and 2.4 samples, respectively, at 2 K.Comment: to appear in Materials Research Expres
Density-of-states fluctuation-induced negative out-of-plane magnetoresistance in overdoped Bi-2212
We analyzed the in-plane and out-of-plane magnetoresistance (MR) for
overdoped BiPbSrCaCuO (Bi-2212) single
crystals using superconductive fluctuation theory, which considers the
density-of-states (DOS) contribution in layered superconductors with the
conventional s-wave pairing state. The out-of-plane results are well reproduced
by the theory, implying that the large, negative out-of-plane MR as well as the
sharp increase in the zero-field out-of-plane resistivity near the
superconducting transition temperature originate from the superconductive
DOS fluctuation effect. On the other hand, the in-plane results are better
reproduced without the DOS contribution (i.e., using only the Aslamazov-Larkin
(AL) contribution), which may be explained in terms of the d-wave
superconductivity of the layered superconductors.Comment: 4 pages, 3 figures, 27th International Symposium on
Superconductivity, ISS 2014, to appear in Physics Procedi
High-entropy effect at rare-earth site in DyNi
We report the structural and magnetic properties of RNi (R=Dy,
TbDyHo, and
GdTbDyHoEr) to investigate the
high-entropy effect at the rare-earth site. The lattice parameters are almost
unchanged by the increase of configurational entropy, which is due to the
successive partial substitution of Dy by pair of rare earth elements located on
both sides of Dy in the periodic table. All compounds exhibit ferromagnetic
ground states. The replacement of Dy with Tb+Ho, which does not have magnetic
interactions in competition with Dy, does not affect the magnetic ordering
temperature. Although (GdTbDyHoEr)Ni
shows the Curie temperature close to that of DyNi, an additional magnetic
anomaly, which would be a spin reorientation, is observed probably due to the
introduction of competing magnetic interactions between R=Gd and Er compounds
and R=Tb, Dy, and Ho ones. We have also assessed the magnetocaloric effect, and
the configurational entropy dependence of the magnetic entropy change reflects
that of the temperature derivative of the magnetic susceptibility. Our analysis
suggests the possibility of enhancing magnetocaloric properties by designing
the anisotropy of rare-earth magnetic moments in the high-entropy state.Comment: to be published in AIP Advance
Fourfold symmetry in the ab plane of the upper critical field for single-crystal Pb2Sr2Y0.62Ca0.38Cu3O8: Evidence for dx2-y2 pairing in a high-Tc superconductor
Pseudogap Phase Boundary in Overdoped Bi_2Sr_2CaCu_2O_8 Studied by Measuring Out-of-plane Resistivity under the Magnetic Fields
The characteristic pseudogap temperature T* in Bi2Sr2CaCu2O8 system has been
systematically evaluated as a function of doping, especially focusing on its
overdoped region, by measuring the out-of-plane resistivity under the magnetic
fields. Overdoped samples have been prepared by annealing TSFZ-grown
Bi2Sr2CaCu2O8 single crystals under the high oxygen pressures (990 kgf/cm2). At
a zero field, the out-of-plane resistivity showed a metallic behavior down to
Tc (= 62 K), while under the magnetic fields of over 3 T,it showed typical
upturn behavior from around 65 K upon decreasing temperature. This result
suggests that the pseudogap and superconductivity are different phenomena.Comment: 2 pages, 2 figures. Final version accepted for the Proceedings of the
M2S-IX Conference (Tokyo, September 2009
Magnetic field effect on Fe-induced short-range magnetic correlation and electrical conductivity in BiPbSrCuFeO
We report electrical resistivity measurements and neutron diffraction studies
under magnetic fields of
BiPbSrCuFeO, in which hole
carriers are overdoped. This compound shows short-range incommensurate magnetic
correlation with incommensurability , whereas a Fe-free compound
shows no magnetic correlation. Resistivity shows an up turn at low temperature
in the form of and shows no superconductivity. We observe reduction
of resistivity by applying magnetic fields (i.e., a negative magnetoresistive
effect) at temperatures below the onset of short-range magnetic correlation.
Application of magnetic fields also suppresses the Fe induced incommensurate
magnetic correlation. We compare and contrast these observations with two
different models: 1) stripe order, and 2) dilute magnetic moments in a metallic
alloy, with associated Kondo behavior. The latter picture appears to be more
relevant to the present results.Comment: 7 pages, 5 figure