Field dependence of the electronic phase separation in Pr0.67Ca0.33MnO3 by small-angle magnetic neutron scattering (original) (raw)
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Journal of Physics: Condensed Matter, 2016
With the goal of elucidating the background of photoinduced ferromagnetism phenomena observed in the perovskite structured (Pr,Ca) manganites, the low-temperature magnetostructure of the material Pr Ca MnO 0.9 0.1 3 was revised using cold neutron powder diffraction, SQUID magnetometry and ab initio calculations. Particular emphasis was placed on determining the presence of nanoscale magnetic phase separation. Previously published results of a canted A-AFM average ground state were reproduced to a good precision both experimentally and theoretically, and complemented by investigating the effects of an applied magnetic field of 2.7 T on the magnetostructure. Explicit evidence of nanoscale magnetic clusters in the material was obtained based on high-resolution neutron diffractograms. Along with several supporting arguments, we present this finding as a justification for extending the nanoscale magnetic phase separation model of manganites to the material under discussion despite its very low Ca doping level in the context of the model. In the light of the new data, we also conclude that the low temperature magnetic moment of Pr must be ca. 300% larger than previously thought in this material, close to the high spin value of µ 2 B per formula unit.
Signature of magnetic phase separation in the ground state of Pr1−xCaxMnO3
Physical Review B, 2008
Neutron scattering has been used to investigate the evolution of the long-and short-range chargeordered (CO), ferromagnetic (FM), and antiferromagnetic (AF) correlations in single crystals of Pr1−xCaxMnO3. The existence and population of spin clusters as reflected by short-range correlations are found to drastically depend on the doping (x) and temperature (T). Concentrated spin clusters coexist with long-range canted AF order in a wide temperature range in x = 0.3 while clusters do not appear in x = 0.4 crystal. In contrast, both CO and AF order parameters in the x = 0.35 crystal show a precipitous decrease below ∼ 35 K where spin clusters form. These results provide direct evidence of magnetic phase separation and indicate that there is a critical doping xc (close to x = 0.35) that divides the phase-separated site-centered from the homogeneous bond-centered or charge-disproportionated CO ground state.
Physical Review B, 2003
The magnetic and transport properties of the Pr 1Ϫx Ca x MnO 3 system were studied at the characteristic points of the phase diagram corresponding to the ferromagnetic insulating and charge-ordered antiferromagnetic states. The magnetization M and resistivity of the ceramic samples with xϭ0.2, 0.25, 0.27, 0.29, 0.30, and 0.33 were measured at temperatures Tϭ4 -300 K and applied magnetic fields H up to 7 T. It was shown that the Curie temperature T C exhibits a nonmonotonic change with x. The maximum value of T C was achieved at xϭ0.25. The isotope substitution 16 O→ 18 O was performed for the samples with xϭ0.2,0.25, and 0.30. A pronounced isotope effect in T C was found. A noticeable drop in the activation energy E a below the Curie temperature and a decrease of resistivity in the magnetic field both in the ferromagnetic insulator phase and in the phase-separated region at xϾ0.3 were observed. Special attention is paid to the possible manifestations of the phase separation in the ferromagnetic insulating state.
Physical Review B, 2005
This article studies the intrinsic influence of hole doping ͑n = 0.5+ ␦͒ on the structural and magnetic phases of the Pr 0.5−␦ Ca 0.2+␦ Sr 0.3 MnO 3 ceramic manganite. Neutron thermodiffractograms are reported for samples with n = 0.46, 0.48, 0.50, 0.52, and 0.54 ͑␦ = −0.04, −0.02, 0.0, 0.02, 0.04͒ in the temperature range 10 K ഛ T ഛ 300 K, as well as high-resolution neutron-diffraction experiments for selected samples and temperatures. We observe structural and magnetic phase coexistence for all the studied compositions and discuss the temperature evolution of the lattice parameters, phase fractions, and magnetic moments of the observed phases. For hole dopings n Ͻ 1 2 , the ground state at low temperature is ferromagnetic, while for n Ͼ 1 2 , it is CE-type antiferromagnetic with Mn 3+ and Mn 4+ spatial order. An extra A-type antiferromagnetic phase is also observed for n Ͼ 1 2 . Our results clearly show the strong coupling between the structural phases and the macroscopic magnetic behavior of the system. The temperature dependence of the magnetization and the hole doping influence are discussed in terms of phase separation.
Small-angle neutron-scattering study of the microphase separation in the Pr0.66Ca0.33MnO3 manganite
Physica B: Condensed Matter, 2004
We report a SANS study of the microphase separation texture of a Pr 0.66 Ca 0.33 MnO 3 crystal as a function of temperature. At T C , ferromagnetic domains display elongated shapes randomly oriented with respect to the crystalline structure, which transform, at lower temperatures, in a texture of randomly oriented and polydisperse 2D sheets of 2 nm average thickness. r
Magnetocaloric effect and nature of magnetic transition in nanoscale Pr0.5Ca0.5MnO3
Journal of Applied Physics, 2012
Systematic measurements pertinent to the magnetocaloric effect and nature of magnetic transition around the transition temperature are performed in the 10 nm Pr 0.5 Ca 0.5 MnO 3 nanoparticles (PCMO10). Maxwell's relation is employed to estimate the change in magnetic entropy. At Curie temperature (T C) ~ 83.5 K, the change in magnetic entropy (-∆S M) discloses a typical variation with a value 0.57 J/kg K, and is found to be magnetic field dependent. From the area under the curve (∆S vs T), the refrigeration capacity (RC) is calculated at T C ~ 83.5 K and it is found to be 7.01 J/kg. Arrott plots infer that due to the competition between the ferromagnetic and anti-ferromagnetic interactions, the magnetic phase transition in PCMO10 is broadly spread over both in temperature as well as in magnetic field coordinates. Upon tuning the particle size, 2 size distribution, morphology, and relative fraction of magnetic phases, it may be possible to enhance the magnetocalorific effect further in PCMO10.
Phase separation effects in charge-ordered Pr 0.5 Ca 0.5 MnO 3 thin film
The European Physical Journal B - Condensed Matter, 2003
Compressed P r0.5Ca0.5M nO3 films (250nm) deposited on LaAlO3 have been studied by Electron Spin Resonance technique under high frequency and high magnetic field. We show evidences for the presence of a ferromagnetic phase (FM) embedded in the charge-order phase (CO), in form of thin layers which size depends on the strength and orientation of the magnetic field (parallel or perpendicular to the substrate plane). This FM phase presents an easy plane magnetic anisotropy with an anisotropy constant 100 times bigger than typical bulk values. When the magnetic field is applied perpendicular to the substrate plane, the FM phase is strongly coupled to the CO phase whereas for the parallel orientation it keeps an independent ferromagnetic resonance even when the CO phase becomes antiferromagnetic.
Charge-order melting and magnetic phase separation in thin films of Pr0.7Ca0.3MnO3
Physical Review B, 2009
We investigate the effect of strain on the phenomenon of charge-order melting, that is the transformation of a charge-ordered insulating state to a metallic state under the influence of a magnetic field ͑the melting field͒ in thin films of Pr 0.7 Ca 0.3 MnO 3 grown on various substrates. We find that unstrained films grown on SrLaGaO 4 behave quite similar to bulk material, but that strained films grown on SrTiO 3 and NdGaO 3 show hugely increased melting fields. Strain relaxation by postannealing again leads to bulklike behavior. In this material the antiferromagnetic charge-order phase can coexist with a ferromagnetic insulating state. Magnetization measurements, where we demonstrate the presence of exchange bias effects, show that this is also the case in the strained films. We argue that the phase mixture in the strained films is more difficult to melt than in the unstrained case.
Small angle neutron scattering study of magnetic clustering in (Pr0.55Ca0.45)(Mn1−yCry)O3 manganites
Journal of Alloys and Compounds, 2012
In the present paper we report a small angle neutron scattering (SANS) study of magnetic clusters formation in (Pr 0.55 Ca 0.45)(Mn 1Ày Cr y)O 3 (y = 0.00, 0.03, 0.06) manganites which was performed by analyzing, above and below the magnetic phase transitions, the momentum transfer q dependence of the SANS intensity on temperature and on the applied magnetic field 0 < H < 5 T. Thermal scans between 5 and 300 K in zero field, 1 and 5 T as well as isothermal field-scans at three different temperatures were collected in the suitable q range on each sample. These measurements allowed us to determine the spatial dimensions, density and distribution of the non-overlapping ferromagnetic clusters before, during and after their formation, both in the insulating high temperature and in the percolating low temperature phases. Our results indicate that the magnetic clusters formation is favoured by Mn/Cr partial substitution, thus emphasizing the importance of magnetic polarons in the natural tendency of manganites to phase separation and the possibility to tune by chemical substitution the relative weight of one phase component with respect to the other one.