Interplay between the Crystalline and Magnetic Structures in BiOCu_0.94S

Abstract

We report on the results of neutron diffraction studies made on a slightly Cu-deficient BiOCu 0.94 S sample. The sample BiOCu 0.94 S crystallizes into a tetragonal P4/nmm symmetry with cell parameters of a=b=3.8591 Å and c=8.5540 Å at 250 K. The magnetic order parameter measurements reveal an inflection point at 250 K, signaling the ferromagetic ordering of the Cu spins. An antiferromagnetic component develops below 180 K, when the crystalline unit cell experiences a sharp thermal contraction upon cooling. This results in a canted ferromagnetic spin arrangement at low temperatures, with a saturated moment of < Z >=0.61(2) B at 3.7K.KEYWORDS: oxysulphide, neutron diffraction, magnetic structureThe strong interplay between the lattice, charge and spin has generated a great variety of intriguing properties in manganese containing compounds with a perovskite structure. [1][2][3][4][5][6] Concurrent transitions from a paramagnetic tetragonal phase to an antiferromagnetic orthorhombic phase have been observed in AFe 2 As 2 , where A is Ba or Sr or Ca. [7][8][9] On the other hand, the antiferromagnetic ordering of the Fe ions and the tetragonal-to-orthorhombic structural transition observed in RFeAsO, where R is La or Nd or Sm or Pr, can be suppressed by F-doping onto the O sites. Interestingly, the kink observed 10) in the resistivity of LaFeAsO has been identified to be associated with the lowering of the crystalline symmetry and the antiferromagnetic ordering of the Fe ions. It has also been shown 11) that CeFeAsO undergoes a lattice distortion from a tetragonal to an orthorhombic structure near 155 K, followed by the formation of an antiferromagnetic ordering on the Fe ions below 140 K. In these iron-based superconducting systems, it is the structural phase transitions that accompany the onset of magnetic ordering. Here, we present the results of investigations made using neutron diffraction measurements on a polycrystalline BiOCu 0.94 S sample. We focus on the interplay between the crystalline and magnetic structures. A change in the magnetic structure appeared when the crystalline experience a sharp thermal contraction upon cooling to below 180 K. No superconductivity is found from the resistivity and magnetization measurements upon cooling to 1.8 K.A polycrystalline sample with a nominal composition of BiOCuS was synthesized by the conventional solid-state reaction technique. The stoichiometric precursor and well mixed powders of Bi, Bi 2 S 3 , and CuO were pelletized and sealed in an evacuated quartz tube with an atmospheric pressure of 10 3 torr. The sealed quartz tubes containing the pellets were heated at 550°C for 15 hours. This was followed by furnace-cooling to room temperature at a rate of 150 °C/h. The resultant compounds were in dark black and very brittle. X-ray diffraction was first used to check the sample, pellet by pellet. No obvious differences were found in the x-ray diffraction patterns taken from different portions of the sample. The sample thus obtained was characterized by neutron diffractio...

Spin, charge and lattice couplings in Cu-deficient oxysulphide BiOCu0.94S

“…It can be seen that the magnetic intensity of the {102} + {003} reflection drops noticeably upon cooling from 180 to 100 K; while the thermal variation rate of the {112} + {103} intensity exhibits a noticeable change at 150 K. The thermal characteristics of the magnetic intensities, as seen in figures 6 and 11, reflect the occurrence of a moment reorientation. A canted ferromagnetic spin arrangement, with a saturated moment of µ Z = 0.61 µ B at 3.7 K, has been reported [27]. The low temperature magnetic phase can be viewed as consisting of a ferromagnetic (FM) component that points 30 • and 60 • away from the crystallographic c-axis and b-axis directions, respectively, and an antiferromagnetic (AFM) component that points in the crystallographic [ 110] direction, with the AFM moment being 58% the strength of the FM moment.…”

“…The low temperature magnetic phase can be viewed as consisting of a ferromagnetic (FM) component that points 30 • and 60 • away from the crystallographic c-axis and b-axis directions, respectively, and an antiferromagnetic (AFM) component that points in the crystallographic [ 110] direction, with the AFM moment being 58% the strength of the FM moment. The AFM component disappears above 180 K, leaving a simple ferromagnetic structure with a magnetic moment of µ Z = 0.31 µ B for the Cu ions at 180 K [27].…”

Large magnetoresistance and charge transfer between the conduction and magnetic electrons in layered oxyselenide BiOCu0.96Se

“…11 Superconductivity has been found in Cu-deficient BiOCu 1−x S. 10 However, superconductivity appears in some but not all of the BiOCuS compounds fabricated using different chemical routes. [12][13][14][15][16] It is now believed that copper deficiency plays a key role in supporting superconductivity in this class of materials. On the other hand, relatively high Seebeck coefficients have been observed in the Sr-doped Bi 1−x Sr x OCuSe, 17 but the physical properties reported for the parent compound BiOCuSe are still limited.…”