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Register a new userPossible Magnetic separation in Ru doped La0.67Ca0.33MnO3
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X-ray diffraction, resistivity, ac susceptibility and magnetization studies on La0.67Ca0.33Mn1-xRuxO3 (0 x < 0.1) were carried out. A significant increase in the lattice parameters indicated the presence of mixed valance state of Ru: Ru3+ and Ru4+. The resistivity of the doped compounds exhibited two features: a broad maximum and a relatively sharp peak. While a para to ferromagnetic transition could be observed for the latter peak, no magnetic signal either in ac susceptibility or in magnetization measurements could be observed for the broad maximum. The magnetic moment decreases non linearly from 3.55 to 3 mB over the Ru composition from 0 to 8.5 at.%. Based on the results of the present studies and on existing literature on the Mn-site substituted systems, we argue that a magnetic phase separation occurs in the Ru doped system. While the sharp peak in the resistivity corresponds to Ru4+ enriched region with a ferromagnetic coupling with neighboring Mn ions, the broad peak corresponds to a Ru3+ rich regions, with an antiferromagnetic coupling with neighboring Mn ions.
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This paper is in continuation of our previous work on the structural, electrical and magnetic properties of Ru doped La(0.67)Ca(0.33)MnO(3) compounds (Ref.: L.Seetha Lakshmi et.al, J. Magn. Magn. Mater. 257, 195 (2003)). Here we report the results of magnetotransport measurements on La(0.67)Ca(0.33)Mn(1-x)Ru(x)O(3) (0<x< 0.1) compounds in the light of proposed magnetic phase separation.
In this report we show that in the perovskite manganite La_{1-x}Ca_{x}MnO_3 for a fixed x approx 0.33, the magnetic transition changes over from first order to second order on reducing the particle size to nearly few tens of a nanometer. The change-over is brought about only by reducing the size and with no change in the stoichiometry. The size reduction to an average size of about 15 nm retains the ferromagnetic state albeit with somewhat smaller saturation magnetization and the ferromagnetic transition temperature T_{C} is suppressed by a small amount (4%). The magnetization of the nanoparticles near T_{C} follow the scaling equation $M/|epsilon|^beta = f_pm(H/|epsilon|^{gamma+beta})$, where, $epsilon = |T-T_C|/T_C$. The critical exponents, associated with the transition have been obtained from modified Arrott plots and they are found to be $beta=0.47pm 0.01$ and $gamma=1.06pm 0.03$. From a plot of M vs H at T_{C} we find the exponent $delta=3.10 pm 0.13$. All the exponents are close to the mean field values. The change-over of the order of the transition has been attributed to a lowering of the value of the derivative dT_{C}/dP due to an increased pressure in the nanoparticles arising due to size reduction. This effect acts in tandem with the rounding off effect due to random strain in the nanoparticles.
The solid solution between the ferromagnetic metal SrRuO$_3$ and the enhanced paramagnetic metal SrRhO$_3$ was recently reported [K. Yamaura et al., Phys. Rev. B 69 (2004) 024410], and an unexpected feature was found in the specific heat data at $x$=0.9 of SrRu$_{1-x}$Rh$_x$O$_3$. The feature was reinvestigated further by characterizing additional samples with various Ru concentrations in the vicinity of $x$=0.9. Specific heat and magnetic susceptibility data indicate that the feature reflects a peculiar magnetism of the doped perovskite, which appears only in the very narrow composition range 0.85$<$$x$$le$0.95.
Using pulsed laser deposition and a unique fast quenching method, we have prepared SrCoOx epitaxial films on SiTiO3 substrates. As electrochemical oxidation increases the oxygen content from x = 2.75 to 3.0, the films tend to favor the discrete magnetic phases seen in bulk samples for the homologous series SrCoO(3-n/8) (n = 0, 1, 2). Unlike bulk samples, 200nm thick films remain single phase throughout the oxidation cycle. 300 nm films can show two simultaneous phases during deoxidation. These results are attributed to finite thickness effects and imply the formation of ordered regions larger than approximately 300 nm.
A series of manganites Tb1-xHoxMnO3 (0<=x<=0.6) with orthorhombic structure are synthesized and detailed investigations on their multiferroicity are performed. Successive magnetic transitions upon temperature variation are evidenced for all samples, and both the Mn3+ spiral spin ordering and rare-earth spin ordering are suppressed with increasing x. Significant enhancement of both the polarization and magnetoelectric response within 0.2<x<0.4 is observed, which may be ascribed to the competition possibly existing between spiral and E-type spin orders. Theoretical calculation is given based on two eg-orbital double-exchange model, and the result supports the scenario of the multiferroic phase separation.
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