Floating zone crystal growth and magnetic properties of bilayer manganites Pr(Sr1−xCax)2Mn2O7

Deng, Guochu; Thiyagarajan, R.; Radheep, D. Mohan; Pomjakushina, E.; Medarde, M.; Krztoń‐Maziopa, A.; Wang, Shuang; Arumugam, S.; Conder, K.

doi:10.1016/j.jcrysgro.2012.04.024

Cited by 6 publications

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“…13 The thermally induced rotation of orbital stripes between these two ordering phases has attracted extensive interest. [14][15][16][17][18] However, the limited information about its microstructures has obstructed a better understanding of the macro properties and physics underneath. Therefore, we carried out a transmission electron microscopy (TEM) study on PrCa 2 Mn 2 O 7 to reveal the different aspects of the microstructure.…”

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“…17,18 Powdered samples, deposited on a Cu grid coated with a holey carbon film, as well as Ar-ion milled TEM samples were used for TEM investigation. A Tecnai G 2 electron microscope equipped with a Gatan cooling and heating holder operated at 200 kV was used to record electron diffraction (ED) patterns, high resolution TEM (HRTEM) images, and carry out in situ TEM observations.…”

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Microstructure of bilayer manganite PrCa2Mn2O7 showing charge/orbital ordering

Tian

Deng

et al. 2013

Applied Physics Letters

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The microstructure of the charge/orbital ordering Ruddleden-Popper phase PrCa 2 Mn 2 O 7 was studied by transmission electron microscopy along both the [001] and the [110] orientation. Three coexisting charge/orbital ordering phases CO1, CO2, and CO3 were observed along the [001] orientation at room temperature. Different from the one-dimensional modulation in the CO1 and CO2 phase, the CO3 phase is characterized by two sets of mutually perpendicular structural modulations. From [110] high angle annular dark field-scanning transmission electron microscopy, we found that the Pr atoms locate in-between the bilayer MnO 6 octahedra, which is different from the previous reports. The strongly correlated electronic systems of perovskite manganites have received great attention because of their fascinating physical properties such as colossal magnetoresistance and high spin polarity, which could find potential applications in spintronics or magnetic tunnel junction. [1][2][3][4][5][6][7][8][9] The physical mechanism of these properties was ascribed to the complicated interplays between the four degrees of freedom of lattice, charge, orbital, and spin, and the consequent ordering as well as possible phase separation. 6,[10][11][12] Recently, two distinct charge/orbital ordering (CO/OO) states were found in the Ruddlesden-Popper (RP) compound Pr(Sr 1Àx Ca x ) 2 Mn 2 O 7 . 13 Pr(Sr 1Àx Ca x ) 2 Mn 2 O 7 has a layer structure (AO) (ABO 3 ) n (n ¼ 2), where two (ABO 3 ) perovskite layers are separated by a AO rock salt layer along the long axis. The two reported CO/OO phases in Pr(Sr 0.1 Ca 0.9 ) 2 Mn 2 O 7 are the high-temperature phase CO1 phase at 330 K > T > 295 K (lattice parameters a ¼ 0.5412, b ¼ 1.0921, c ¼ 1.9234 nm, and space group Pbnm) and the lower-temperature CO2 phase at T < 295 K (a ¼ 1.0812, b ¼ 0.5475, c ¼ 1.9203 nm, and space group Am2m, Ref. 13). The CO1 phase is centrosymmetric without any spontaneous electric polarization, but the CO2 phase is a noncentrosymmetric phase with spontaneous electric polarization. 13 The thermally induced rotation of orbital stripes between these two ordering phases has attracted extensive interest. [14][15][16][17][18] However, the limited information about its microstructures has obstructed a better understanding of the macro properties and physics underneath. Therefore, we carried out a transmission electron microscopy (TEM) study on PrCa 2 Mn 2 O 7 to reveal the different aspects of the microstructure. The phases and micro domains viewed along the [001] zone axis are discussed. The heavy Pr atoms were found to locate inbetween the bilayer MnO 6 octahedra.Bulk PrCa 2 Mn 2 O 7 samples were synthesized using a traveling solvent floating zone method with high oxygen background pressure. 17,18 Powdered samples, deposited on a Cu grid coated with a holey carbon film, as well as Ar-ion milled TEM samples were used for TEM investigation. A Tecnai G 2 electron microscope equipped with a Gatan cooling and heating holder operated at 200 kV was used to record electron diffractio...

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Microstructure of bilayer manganite PrCa2Mn2O7 showing charge/orbital ordering

Tian

Deng

et al. 2013

Applied Physics Letters

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“…The crystal sample of PCMO was successfully synthesized by introducing high oxygen partial pressure during the growth in a floating-zone furnace. 15 Thus, for the convenience of comparison, we prepared both the PSMO and PCMO powder samples for the neutron powder-diffraction experiments by pulverizing the crystal rods grown from the floating-zone method. 15 The high-resolution neutron powder diffraction experiments were carried out on the high-resolution neutron diffractometer HRPT 21 at the SINQ spallation source at the Paul Scherrer Institute at both room and low temperature with a wavelength of 1.494 Å .…”

Section: Methodsmentioning

confidence: 99%

“…This is mainly due to the difficulties to synthesize the phase-pure samples of Pr(Sr 1Ày Ca y ) 2 Mn 2 O 7 , especially those with high Ca-doping. 15 This problem has been recently overcome by introducing high oxygen partial pressure in the crystal-growth procedure. 15 Using single-crystal samples, surprisingly, Tokunaga et al 7 discovered rotation of the charge-ordering and orbital-ordering stripes in Pr(Sr 0.1 Ca 0.9 ) 2 Mn 2 O 7 .…”

Section: Introductionmentioning

confidence: 99%

“…15 This problem has been recently overcome by introducing high oxygen partial pressure in the crystal-growth procedure. 15 Using single-crystal samples, surprisingly, Tokunaga et al 7 discovered rotation of the charge-ordering and orbital-ordering stripes in Pr(Sr 0.1 Ca 0.9 ) 2 Mn 2 O 7 . On cooling, the sample shows two different charge-ordering phases: CO1 and CO2, which correspond to the charge-ordering stripes aligning along the a and b axes, respectively.…”

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Chemical pressure effects on crystal and magnetic structures of bilayer manganites PrA2Mn2O7 (A = Sr or Ca)

Deng

Sheptyakov

Pomjakushin

et al. 2016

Journal of Applied Physics

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The crystal and magnetic structures of the bilayer manganites PrSr 2 Mn 2 O 7 (PSMO) and PrCa 2 Mn 2 O 7 (PCMO) have been studied by neutron powder diffraction. It was found that PSMO crystallizes in space group I4/mmm, while PCMO adopts space group Cmc2 1 at room temperature. The difference in the structure arises from chemical pressure induced by the Ca substitution for Sr on the A sites, which causes different Jahn-Teller distortions. In PSMO, the MnO 6 octahedra suffer a small elongated distortion, while those in PCMO adopt strong compressed distortion along the axial direction. In addition, the octahedra in PCMO show a þ b 0 c 0 rotation and a 0 b þ c þ tilting in the Glazer notation in comparison to PSMO. As a result, these two compounds adopt very different magnetic structures: The magnetic structure of PSMO is an A-type magnetic structure (Im'm'm) with propagation vector k ¼ (0, 0, 1) and magnetic moments in the ab plane. In contrast, a C-type antiferromagnetic magnetic structure (Cm'c2 0 1) with the multiple propagation vectors (k ¼ (0, 1 2 , 1 2) and (0, 1 2 , 0)) and magnetic moments mainly along the b axis is found in PCMO. The critical exponent of the magnetic phase transition is around 0.345 for PSMO and 0.235 for PCMO, indicating 3D and 2D XY transitions, respectively. The strong Jahn-Teller distortion induced by the chemical pressure is believed to suppress the double exchange and favour super-exchange in PCMO, leading to the dramatic difference in the magnetic structure. Published by AIP Publishing.

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