Search

Abstract: Systematic studies of X-ray, magnetic, electronic transport, and elastic properties have been performed on polycrystalline Bi0.5Ca0.4Sr0.1MnO3 sample. The sample exhibits charge ordering (CO) state below T CO (=304K), accompanied by a distinct maximum in magnetization. The softening of Young''s modulus in the vicinity of T CO indicates that there is a strong coupling of electron–phonon due to Jahn–Teller (JT) effect. The dynamic ferromagnetic spin correlations are observed at high temperatures above T CO, which are replaced by antiferromagnetic (AFM) spin fluctuations at a concomitant CO transition. Below 32K, a spin-glass (SG) state dominates at low temperatures. The voltage–current (V–I) characteristics measurement results indicate that the non-linear conduction starts above a threshold current, giving rise to a region of negative differential resistance (NDR). The origin of the non-linear conduction is discussed in view of current induced collapse of CO state associated with phase-separation mechanism. [Copyright &y& Elsevier]

Abstract: The structural study of Sr0.9Ce0.1Mn1–y Cr y O3 (, 0.05, and 0.10) has been carried out by X-ray diffraction. For undoped sample Sr0.9Ce0.1MnO3, it undergoes a first-order structural transition accompanied by Jahn–Teller (JT) transition at . The JT transition temperature is reduced in Cr-doped samples, becoming for . The tetragonal structure is characterized by the JT distortion in MnO6 octahedra with the distortion mode . With increasing Cr doping content, the deformation of MnO6 octahedra is weakened, showing that Cr doping destabilizes the JT effect. In addition, elastic properties measurement indicates that a large softening of Young''s modulus occurs in the vicinity of , which has been interpreted in terms of the strong electron–phonon coupling originating from the JT effect. [Copyright &y& Elsevier]

Abstract: Cr-doped manganites Sr0.9Ce0.1Mn1−y Cr y O3 (y=0, 0.05, and 0.10) have been systematically investigated by X-ray, magnetic, transport, and elastic properties measurements. For parent compound Sr0.9Ce0.1MnO3, it undergoes a metal–insulator (M–I) transition at 318K, which is suggested to originate from a first-order structural transition accompanied by Jahn–Teller (JT) transition. With increasing Cr doping content, the JT transition temperature decreases. The Cr doping suppresses the antiferromagnetic (AFM) state and makes the system spin-glass (SG) behavior at low temperatures. In the vicinity of JT transition temperatures, the softening of Young''s modulus originating from the coupling of the orbital (quadrupolar) moment of the eg orbital of Mn3+ ion to the elastic strain has been observed. The anomalous Young''s modulus properties imply the electron–phonon coupling due to the JT effect may play an important role in the system. [Copyright &y& Elsevier]

Abstract: The role of vibrational anisotropy of Mn3+O6 octahedron in the phase separation behavior of La0.67−y Pr y Ca0.33MnO3 (x=0, 0.15, 0.25 and 0.30) has been investigated by means of magnetization M, internal friction Q −1, Young''s modulus E along with the X-ray powder diffraction measurements. For the samples with y=0 and 0.15, the Q −1 exhibits three peaks in the ferromagnetic region, which are attributed to the intrinsic inhomogeneity of ferromagnetic phase, i.e. the electronic phase separation with the coexistence of insulating and conducting phases. However, both the samples with y=0.25 and 0.30 undergo a magnetic phase separation with the coexistence of the antiferromagnetic and ferromagnetic phases, and the Q −1 peaks related to the electronic phase separation have not been observed. In addition, the Q −1 exhibits a peak in the paramagnetic region for all samples, which may result from the formation of magnetic clusters. We observed that the evolution from electronic to magnetic phase separation is close related to the rapid increase in the ratio of two kinds of Jahn–Teller distortion modes Q 3 and Q 2, i.e. Q 3/Q 2. A schematic phase diagram is given in the text, and it is suggested that the enhancement of vibrational anisotropy of Mn3+O6 octahedron plays a key role in the evolution from electronic to magnetic phase separation. [Copyright &y& Elsevier]