Showing papers by "M. R. Ibarra published in 2002"
TL;DR: In this article, the composition dependence of magnetic and structural transformations, as well as the temperature and composition of the magnetocrystalline anisotropy, were studied in the martensitic Ni2+xMn1+yGa1+z (x+y+z=0) Heusler alloys.
Abstract: The composition dependence of magnetic and structural transformations, as well as the temperature and composition dependence of the magnetocrystalline anisotropy, were studied in the martensitic Ni2+xMn1+yGa1+z (x+y+z=0) Heusler alloys. Moving away from the stoichiometric composition, a slight variation, a large reduction, and a marked enhancement, were, respectively, observed for the Curie temperature, the magnetic anisotropy, and the structural (martensitic–austenitic) transformation temperatures.
93 citations
TL;DR: In this paper, double perovskites (Ba0.8Sr0.2)2−xLaxFeMoO6 (0⩽x0.4) were investigated to optimize low-field magnetoresistance (LFMR) together with high Curie temperatures (TC).
Abstract: Large low-field magnetoresistance (LFMR) together with high Curie temperatures (TC) are requirements for some applications in magnetoelectronics. In order to optimize both parameters, we have investigated double perovskites (Ba0.8Sr0.2)2−xLaxFeMoO6 (0⩽x⩽0.4). High-temperature neutron diffraction measurements indicate a strong increase in TC with La doping (from ≈345 K for x=0 to ≈405 K for x=0.4). The LFMR is very large for x=0 (at 10 KOe≈27% at 10 K and ≈7% at 290 K) and decreases with La doping. This decrease cannot be attributed to a substantial enhancement of Fe/Mo antisite disorder, which is small as tracked by means of x-ray and high-resolution neutron diffraction, but to grain boundaries modifications.
87 citations
TL;DR: In this article, the paramagnetic ground state of the colossal magnetoresistance (CMR) compound was investigated using a wide set of techniques, including magnetoreduction, magnetization, high-resolution neutron diffraction, small-angle neutron diffusion, and muon spin relaxation.
Abstract: In order to investigate the paramagnetic ground state of the colossal magnetoresistance (CMR) Sm 0 . 5 5 Sr 0 . 4 5 MnO 3 compound we have used a wide set of techniques magnetoresistance, magnetization, high-resolution neutron diffraction, small-angle neutron diffraction, and muon spin relaxation. According to these measurements the paramagnetic ground state would consist of ∼0.8 nm ferromagnetic clusters embedded in a short-range charge/orbital ordered matrix. The CMR effect occurs due to percolation of these ferromagnetic clusters.
85 citations
TL;DR: In this paper, the magnetic-crystallographic temperature-composition phase diagram has been determined over the whole temperature range (2 -300 K) by means of macroscopic (ac magnetic susceptibility, linear thermal expansion, and resistivity) and microscopic neutron powder diffraction experiments.
Abstract: The different magnetic and crystallographic structures in the series of ${\mathrm{Tb}}_{5}({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{)}_{4}$ compounds have been studied by means of macroscopic (ac magnetic susceptibility, linear thermal expansion, and resistivity) and microscopic neutron powder diffraction experiments. As a result, the magnetic-crystallographic temperature-composition phase diagram has been determined over the whole temperature range (2--300 K). We have described in detail the origin of the low-temperature magnetic transitions in pure ${\mathrm{Tb}}_{5}{\mathrm{Ge}}_{4}$ and ${\mathrm{Tb}}_{5}{\mathrm{Si}}_{4}$ alloys. Compounds with $x=0.4,$ 0.5, and 0.6 present a monoclinic ${(P112}_{1}/a)$ structure at room temperature. On cooling down, these materials exhibit a first-order crystallographic-magnetic transformation to an orthorhombic (Pnma) canted-ferromagnetic structure. These results constitute an experimental evidence of the strong coupling between crystallographic and magnetic degrees of freedom in the ${\mathrm{Tb}}_{5}({\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}{)}_{4}$ compounds.
72 citations
TL;DR: In this article, a series of A 2 BB′O 6 double perovskites with a ferrimagnetic ground state was synthesized and studied by means of a wide set of experimental techniques.
55 citations
TL;DR: In this paper, the effects of Mn substitution on the magnetic properties of Er2Fe17−xMnx compounds have been investigated by different experimental techniques, and an unusual composition dependence of the unit cell volume at room temperature occurs due to a strong magnetovolume effect, which has been confirmed by high temperature linear thermal expansion measurements.
Abstract: The effects of Mn substitution on the magnetic properties of Er2Fe17−xMnx compounds have been investigated by different experimental techniques. An unusual composition dependence of the unit cell volume at room temperature occurs due to a strong magnetovolume effect, which has been confirmed by high temperature linear thermal expansion measurements. From magnetization measurements the composition dependence of the spontaneous magnetization of the 3d-sublattice magnetic moment and of the Curie temperature has been determined. Spin reorientation has been detected for compounds with 3⩽x⩽5.5, as well as remarkable magnetic history effects.
39 citations
TL;DR: In this paper, the NMR spin-echo spectra measured on a powder sample of Sr2FeMoO6 at 3 and 77 K at zero field and in an applied magnetic field are reported.
33 citations
TL;DR: In this paper, the existence of nano-and microscopic phase segregation above and below T N 112 K in the electron-doped region of the Sm-Ca phase diagram of manganites can he found in the unique compound Sm 0. 1 5 Ca 0. 8 5 MnO 3.
Abstract: The rich and peculiar macro- and microscopic phenomenology observed in the electron-doped region of the Sm-Ca phase diagram of manganites can he found in the unique and fascinating compound Sm 0 . 1 5 Ca 0 . 8 5 MnO 3 . We report the existence of nano- and microscopic phase segregation above and below T N 112 K. The very different nature of the coexisting phases and the field and temperature dependencies are explained considering the interplay of magnetic and structural correlations, which give rise to different structural and magnetic ground states, close in energies (P-Pnma, G+F-Pnma, G-Pnma, C-P2 1 /m).
23 citations
TL;DR: In this article, the authors measured the thermal expansion of several Fe-rich compounds with the ThMn12 structure, including RFe11.3Nb0.7, YFe11Ti and YFe10Mo2 in the temperature range 150-800 K. The effect of Ni substitution for Fe on the volume effect and on the Curie temperature was analyzed studying the Ho(Fe1� xNix)11.7 compounds.
Abstract: We have measured the thermal expansion of several Fe-rich compounds with the ThMn12 structure. The series RFe11.3Nb0.7 (R=Y, Sm, Gd, Tb, Dy, Ho and Er), Ho(Fe1� xNix)11.3Nb0.7 with x ¼ 020:3; YFe11Ti and YFe10Mo2 have been investigated in the temperature range 150–800 K. In the Fe-rich compounds with stabilizing element T=Nb and Ti, a pronounced positive spontaneous volume magnetostriction has been observed below the Curie temperature. The effect of Ni substitution for Fe on the volume effect and on the Curie temperature has been analyzed studying the Ho(Fe1� xNix)11.3Nb0.7 compounds. The different magnitude of the magnetovolume effect observed in YFe11.3Nb0.7, YFe11Ti and YFe10Mo2 is explained in terms of the classical model for itinerant ferromagnets. r 2002 Elsevier Science
22 citations
TL;DR: In this paper, the authors investigated the magnetic properties of YFe11−xCoxTi compounds and found that the largest spontaneous volume magnetostriction occurs at x=3, close to the concentration in which a maximum in saturation magnetization was found.
Abstract: Thermal expansion and magnetic properties of the YFe11−xCoxTi compounds have been investigated by various experimental methods. A large magnetovolume effect has been clearly observed below TC for the Fe-rich compounds. When the transition metal concentration changes from Fe to Co rich, the invar-like effect becomes less pronounced and almost disappears close to the pure-Co compound. The dependence of the spontaneous volume magnetostriction on temperature and Co concentration has been estimated from the thermal expansion measurements. It has been found that, for the YFe11−xCoxTi compounds, the largest spontaneous volume magnetostriction (about 2.1%) occurs at x=3, close to the concentration in which a maximum in saturation magnetization was found. The anomalous thermal expansion can be attributed to the volume dependence of the magnetic energy, which is very sensitive to the distance between first-neighbors transition-metal atoms for Fe-rich compounds.
13 citations
Journal Article•
TL;DR: In this paper, the magnetic and crystallographic properties of Tb 5 (Si x Ge 1 - x ) 4 compounds have been studied by means of macroscopic (ac magnetic susceptibility, linear thermal expansion and resistivity) and microscopic neutron powder diffraction experiments.
Abstract: The different magnetic and crystallographic structures in the series of Tb 5 (Si x Ge 1 - x ) 4 compounds have been studied by means of macroscopic (ac magnetic susceptibility, linear thermal expansion, and resistivity) and microscopic neutron powder diffraction experiments. As a result, the magnetic-crystallographic temperature-composition phase diagram has been determined over the whole temperature range (2-300 K). We have described in detail the origin of the low-temperature magnetic transitions in pure Tb 5 Ge 4 and Tb 5 Si 4 alloys. Compounds with x = 0.4, 0.5, and 0.6 present a monoclinic (P112 1 /a) structure at room temperature. On cooling down, these materials exhibit a first-order crystallographic-magnetic transformation to an orthorhombic (Pnma) canted-ferromagnetic structure. These results constitute an experimental evidence of the strong coupling between crystallographic and magnetic degrees of freedom in the Tb 5 (Si x Ge 1 - x ) 4 compounds.
TL;DR: In this article, the phonon frequency and width are different for the ferromagnetic (FM) metallic and charge-order (CO) phases due to a difference in the local structure of each phase.
07 Aug 2002
TL;DR: In this article, the authors used Singular Point Detection (SPD) to determine the magnetocrystalline anisotropy field (HA) of a single crystalline Ni/sub 2/MnGa.
Abstract: Summary form only given. Magnetic-field-induced strains of the order of 5% have been recently observed in single crystalline Ni/sub 2/MnGa, under the application of relatively low fields. This ferromagnetic Heusler alloy, which exists in a wide compositional range, crystallizes in the L2/sub 1/ cubic structure. On cooling from high temperatures, it undergoes a martensitic transformation to a complex uniaxial structure, that is magnetically hard. The magnetocrystalline anisotropy of this phase plays an important role in the occurrence of the observed magnetic-field-induced strains. In the present study the samples Ni/sub 2+x/Mn/sub 1-x/Ga with x=0, 0.1, 0.15 and Ni/sub 2/Mn/sub 1+y/Ga/sub 1-y/ with y = 0.06 and 0.12 were prepared. The composition dependence of their magnetic and structural transition temperatures as well as the composition and temperature dependence of the magnetocrystalline anisotropy were studied. The determination of the anisotropy field (HA) values was done by using the Singular Point Detection (SPD) technique, that is a straightforward method applied to polycrystalline materials.