Long-scale phase separation versus homogeneous magnetic state in (La_ {1-y} Pr_ {y}) _ {0.7} Ca_ {0.3} MnO_ {3}: A neutron diffraction study (original) (raw)
Related papers
2008
The crystal and magnetic structure of (La 0.70 Ca 0.30 )(Cr y Mn 1-y )O 3 for y = 0.70, 0.50 and 0.15 has been investigated using neutron powder diffraction. The three samples crystallize in the Pnma space group at both 290 K and 5 K and exhibit different magnetic structures at low temperature. In (La 0.70 Ca 0.30 )(Cr 0.70 Mn 0.30 )O 3 , antiferromagnetic order with a propagation vector k = 0 sets in. The magnetic structure is G x , i.e. of the G-type with spins parallel to the a-axis. On the basis of our Rietveld refinement and the available magnetisation data, we speculate that only Cr 3+ spins order, whereas Mn 4+ act as a random magnetic impurity. In (La 0.70 Ca 0.30 )(Cr 0.50 Mn 0.50 )O 3 the spin order is still of type G x , although the net magnetic moment is smaller. No evidence for magnetic order of the Mn ions is observed. Finally, in (La 0.70 Ca 0.30 )(Cr 0.15 Mn 0.85 )O 3 a ferromagnetic ordering of the Mn spins takes place, whereas the Cr 3+ ions act as random magnetic impurities with randomly oriented spins.
Phase coexistence and magnetocaloric effect in La_{5/8−y}Pr_{y}Ca_{3/8}MnO_{3} (y=0.275)
Physical Review B, 2010
The magnetocaloric effect ͑MCE͒ was measured to probe the nature of phase coexistence of structurally different ferromagnetic metallic ͑FMM͒ and charge-ordered insulating phases in La 5/8−y Pr y Ca 3/8 MnO 3 ͑y = 0.275͒ single crystals. The MCE peaks with both positive and negative values are observed in the vicinity of the multiple-phase transitions in the system. Strain associated with the phase coexistence has been known to stabilize a strain-glass state as well as a strain-liquid state. The large MCE is observed in the "dynamic" strain liquid state, while it is relatively small in the "frozen" strain-glass state. The MCE data reveal that the sharp increase in the magnetization below the Curie temperature in the strain-liquid region is attributed to the enhancement of the FM domain regions that are already present in the material. MCE is also shown to be a useful method to probe the subtle balance of coexisting phases in mixed-phase manganites.
THE STRUCTURAL AND MAGNETIC PROPERTIES OF La 1-X Ca X MnO 3 WITH X = 0.27 AND 0.47
2012
THE STRUCTURAL AND MAGNETIC PROPERTIES OF La 1-x Ca x MnO 3 WITH x = 0.27 AND 0.47. We have studied the structural and magnetic properties for La 1-x Ca x MnO 3 with x = 0.27 and 0.47 using neutron powder diffraction and magnetization measurements. At room and low temperature, all samples have the orthorhombic structure with space group Pnma. The sample x = 0.47 shows the antiferromagnetic mix a ferromagnetic with the magnetic moment and the Curie temperature are 1.30 μ B and 260K, respectivelywhile the sample x = 0.27 is a ferromagnetic with the magnetic momentand the Curie temperature are 3.10 μ B and 197K, respectively.
Physical Review B, 2003
The influence of the 16 O-18 O isotope substitutions on magnetic state of perovskite-type manganite (La 0.25 Pr 0.75) 0.7 Ca 0.3 MnO 3 is studied by 55 Mn NMR. Successive cycling with an isochronal exposure at different magnetic fields up to Hϭ8T is used to study the field-induced transition from antiferromagnetic insulating ͑AFI͒ state to the ferromagnetic metal ͑FMM͒ one in the 18 O-enriched sample. After exposure at H ϾH cr ϳ 5.3T the NMR spectrum of the 18 O sample provides evidence for a magnetic phase separation ͑PS͒ into the coexisting AFI and FMM domains. Further increase of exposing field leads to a progressive growth of the FMM phase at the expense of AFI domains. Its relative fraction can be controlled by external magnetic field and the resulting magnetic structure in the PS region is discussed. Anomalous T dependence of the 55 Mn nuclear spin-lattice relaxation rate is revealed in the FMM state of both 16 O-and 18 O-enriched samples. The possible influence of the Pr magnetic ordering at Tϳ40 K on the spin-lattice relaxation is considered.
Physical Review B, 2012
Bulk manganites of the form La 5/8−y Pr y Ca 3/8 MnO 3 (LPCMO) exhibit a complex phase diagram due to coexisting charge-ordered antiferromagnetic (CO/AFM), charge-disordered paramagnetic (PM), and ferromagnetic (FM) phases. Because phase separation in LPCMO occurs on the microscale, reducing particle size to below this characteristic length is expected to have a strong impact on the magnetic properties of the system. Through a comparative study of the magnetic and magnetocaloric properties of single-crystalline (bulk) and nanocrystalline LPCMO (y = 3/8) we show that the AFM, CO, and FM transitions seen in the single crystal can also be observed in the large particle sizes (400 and 150 nm), while only a single PM to FM transition is found for the small particles (55 nm). Magnetic and magnetocaloric measurements reveal that decreasing particle size affects the balance of competing phases in LPCMO and narrows the range of fields over which PM, FM, and CO phases coexist. The FM volume fraction increases with size reduction, until CO is suppressed below some critical size, ∼100 nm. With size reduction, the saturation magnetization and field sensitivity first increase as long-range CO is inhibited, then decrease as surface effects become increasingly important. The trend that the FM phase is stabilized on the nanoscale is contrasted with the stabilization of the charge-disordered PM phase occurring on the microscale, demonstrating that in terms of the characteristic phase separation length, a few microns and several hundred nanometers represent very different regimes in LPCMO.
The European Physical Journal B, 2001
The atomic structure of (La1−yPry)0.7Ca0.3MnO3 compound with 0.5 ≤ y ≤ 1 has been systematically studied by neutron powder diffraction in the temperature range from 15 to 293 K. For composition with y = 0.75, the structural analysis was performed on two samples, one containing the natural mixture of oxygen isotopes and the other one 75% enriched by 18 O. The room temperature structural characteristics of the series, including cell volume, average Mn-O bond distance, and average Mn-O-Mn bond angle, are the linear functions of the rA . Temperature dependencies of these parameters are quite smooth, except for the point T = TFM, where a jump like changes occur. The isotope enriched samples have been found identical in crystal and magnetic structure down to the temperature of transition of the sample with 16 O into the metallic ferromagnetic phase. It confirms that different transport and magnetic properties of the samples with 16 O and 18 O at low temperature are driven by the different oxygen atoms dynamics solely. Temperature dependencies of the CO and AFM diffraction peak intensities and of the peak widths for compositions close to the metal-insulator boundary (y ≈ 0.75) indicate the macroscopically phase separated AFM-dielectric + FM-metallic state below TFM. PACS. 75.30.Vn Colossal magnetoresistance -61.12.Ld Single-crystal and powder diffraction
Unconventional Ferromagnetic Transition in La_ {1-x} Ca_ {x} MnO_ {3}
Physical review letters, 1996
Neutron scattering has been used to study the magnetic correlations and long wavelength spin dynamics of La 1-x Ca x MnO 3 in the ferromagnetic regime (0≤x<1 / 2). For x = 1 / 3 (T C = 250 K) where the magnetoresistance effects are largest the system behaves as an ideal ...
Imaging the First-Order Magnetic Transition in La_{0.35}Pr_{0.275}Ca_{0.375}MnO_{3}
Physical Review Letters, 2012
The nature of the ferromagnetic, charge, orbital, and antiferromagnetic order in La 0:35 Pr 0:275 Ca 0:375 MnO 3 on the nano-and microscale was investigated by photoemission electron microscopy (PEEM) and resonant elastic soft x-ray scattering (RSXS). The structure of the ferromagnetic domains around the Curie temperature T C indicates that they nucleate under a high degree of lattice strain, which is brought about by the charge, orbital, and antiferromagnetic order. The combined temperaturedependent PEEM and RSXS measurements suggest that the lattice distortions associated with charge and orbital order are glassy in nature and that phase separation is driven by the interplay between it and the more itinerant charge carriers associated with ferromagnetic metallic order, even well below T C .
Phase separations in La0.7−xDyxCa0.3Mn(Fe)O3
Mössbauer spectroscopy of La 0.7−x Dy x Ca 0.3 Mn͑Fe͒O 3 shows phase separation, both above and below T C . The behavior in the two regions are independent and related to different phenomena. Above T C , the phase splitting is due to different lattice distortions. In one of the phases, Jahn-Teller distortion is significant. Below T C , the spin orderings in the two phases are ferromagnetic ͑FM͒ and spin glass ͑SG͒ orderings, respectively. At low temperatures, SG phase converts into FM phase when the applied magnetic field increases, but only partially. We find a drastic increase in magnetoresistivity ͑MR͒ as x is increased beyond 0.07. It attains a maximum value for x Ϸ 0.12 ͑greater than 750 000%͒ and decreases again rapidly as x increases. We have provided an explanation for the high MR in x = 0.12 phase. Other differences between the compositions studied here can also be identified. First, the phase with Jahn-Teller distortion disappears when the temperature is lowered to T C in a composition with x ജ 0.12. This is not the case when x = 0.07. Second, we observe anomalous hysteresis loop when x = 0.12. The anomaly is less pronounced in other compositions. Third, in composition x = 0.07, the hyperfine magnetic fields ͑H int ͒ in FM and SG components are distinctly different. This is not so when x = 0.12.