Search

Highlights • The magnetic properties of ordered double perovskite Pb 2 FeSbO 6 were studied in details. • Unexpected long-range antiferromagnetic ordering in Pb 2 FeSbO 6 compound was found. • The antiferromagnetic phase in Pb 2 FeSbO 6 formed on the cation disordering structural domains. • The propagation vector of the antiferromagnetic phase is q = (½, ½, 0). • Under cooling, the structural phase transition in Pb 2 FeSbO 6 occurs. Abstract The structural and magnetic ordering of Pb 2 FeSbO 6 was studied by means of Mössbauer spectroscopy and neutron powder diffraction in the temperature range from 5 to 300 K. The structural phase transition from the initial cubic phase Fm 3 ¯ m to the tetragonal I 4 / m phase was observed in temperature range 170–190 K. The antiferromagnetic order with a propagation vector q = (½, ½, 0) was found at temperature T < T N = 30 K. The temperature dependences of the hyperfine parameters of Mössbauer spectra and magnetic moments for Pb 2 FeSbO 6 at low temperatures were obtained. The relationships between the short-range cation ordering observed by Mossbauer spectroscopy and the long-range cation ordering observed by neutron powder diffraction are discussed. [ABSTRACT FROM AUTHOR]

• Suppression of the low temperature cone structure under pressure. • Rapid pressure-induced increase of the lock-in transition temperature. • Significant increase of commensurate q z component of the helical structure up to ¼ c * below the lock-in transition. • Magnetic P-T phase diagram of elemental Ho. The pressure response of the magnetic and structural properties of elemental holmium was explored by means of neutron powder diffraction in the pressure range up to 8.7 GPa and the temperature range 7 – 290 K. At ambient pressure, below T N = 127 K the incommensurate helical state with a propagation vector q = (0 0 q z) is evidenced. On temperature lowering, the q z value decreases from 0.270 c * (at 125 K) to 5/26 c * at T L = 20 K. Below the lock-in transition temperature T L , a commensurate cone structure is formed due to canting of magnetic moments towards the c axis. Upon lattice compression, a gradual suppression of the low temperature cone structure was found and just a helical state was observed above 4 GPa. This state is incommensurate in the temperature range T L < T < T N and becomes commensurate below T L. At T = 7 K, the q z component evolves towards ¼ c * value at 8.7 GPa. The Néel temperature decreases to 108 K with a pressure increase up to 8.7 GPa with a pressure coefficient dT N /dP ≈ −2.2 K/GPa, while the lock-in transition temperature exhibits opposite behavior and grows up to about 50 K with a coefficient of dT L /dP ≈ 3.4 K/GPa. The magnetic P - T phase diagram of Ho is constructed. The compression of Ho lattice at T = 7 K is nearly isotropic, as found from about the same compressibilities of the a and c axes. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of doped ferrite Zn 0.3 Cu 0.7 Fe 1.5 Ga 0.5 O 4 have been studied by means of the neutron diffraction method at high pressures up to 4.7 GPa and in temperature range 300–425 K. By increasing the temperature and the pressure, a gradual suppression of the magnetic moments of iron ions in both A and B crystallographic sites was observed. This effect corresponds to a magnetic phase transition from the ferrimagnetic state to paramagnetic one. The lattice parameters, interatomic bond lengths and angles, magnetic moments of iron ions as functions of temperature and pressure were obtained. Upon compression, the magnetic ordering temperature of studied ferrite decreases with a large pressure coefficient dT c / dP  = −19(1) K × GPa −1 . [ABSTRACT FROM AUTHOR]

• A significant suppression of the ordered magnetic moment at high pressure is observed, associated with enhancement of spin fluctuations. • The pressure increase of Neel temperature is more pronounced with respect to other hexagonal RMnO 3 compounds. • A change of the ground magnetic state symmetry from mixed Г 1 + Г 2 to pure Г 1 irreducible representation is expected at pressure of about 6 GPa. The crystal and magnetic structures of hexagonal manganite ScMnO 3 have been studied by means of neutron diffraction at high pressures up to 2 GPa in the temperature range 10–300 К. At ambient pressure below T N = 130 K the triangular antiferromagnetic (AFM) state of mixed Г 1 + Г 2 irreducible representation is formed. Upon application of high pressure, the symmetry of magnetic structure persists up to 2 GPa. A significant suppression of the ordered magnetic moment and gradual spin reorientation were revealed under pressure. The baric dependence of Neel temperatures T N was obtained with the average linear pressure coefficient dT N / d P = 6.9 K/GPa, which is significantly larger with respect to related compounds like YMnO 3. For the data obtained, one may expect modification of the magnetic ground state symmetry to the pure Г 1 representation at pressures about 6 GPa. [ABSTRACT FROM AUTHOR]

• Formation of complex modulated commensurate states under pressure. • Suppression of temperature range of intermediate incommensurate magnetic states under pressure. • Positive pressure coefficients of Néel and lock-in transition temperatures. The magnetic and structural properties of elemental thulium were studied by means of neutron powder diffraction at pressures up to 5.5 GPa in the temperature range 7 – 290 K. At ambient pressure below T N = 52 K, the incommensurate magnetic state with a longitudinal sinusoidal modulation and propagation vector q = (0, 0, q z) was formed. The q z value increases on cooling from 0.279(2) and reaches the commensurate value of 2/7 at the temperature T 1 = 24 K. The new magnetic arrangement is of an antiphase domain structure, composed of structural blocks involving three or four hexagonal layers with magnetic moment directions parallel within a given block and oppositely alternating from block to block along the c axis. Under high pressure, the T N value increases slightly up to 57 K at 5.5 GPa with a pressure coefficient dT N /dP = 0.9 K/GPa. The pressure dependence of the T 1 temperature is more pronounced with a pressure coefficient dT 1 /dP = 2.9 K/GPa. The arrangement of commensurate magnetic structures formed below T 1 is strongly pressure dependent. A formation of the complex magnetic states composed of structural blocks involving three or four hexagonal layers with magnetic moment signs alternating from block to block along the c axis with q z = 7/23 at 2 GPa and q z = 7/22 at 5.5 GPa was observed. The lattice compression of Tm at T = 7 K demonstrates a weak anisotropy with the most compressible c axis. [ABSTRACT FROM AUTHOR]

• A phase coexistence of hcp and Sm-type phases is found in 160Gd at ambient conditions. • The hcp phase and FM order are rapidly suppressed under pressure. • In the Sm-type phase, stabilized by pressure, the AFM order is formed. Structural and magnetic properties of the isotopically substituted 160Gd metal (97.5 % enrichment) were studied by means of neutron powder diffraction at pressures up to 9 GPa in the temperature range 7 – 290 K. At ambient conditions, a coexistence of hexagonal close packed (hcp) and Sm-type rhombohedral phases was observed. Under high pressure, the hcp phase was suppressed gradually and above 6 GPa only the Sm-type phase is observed. The long range ferromagnetic order formed in the hcp phase is also suppressed rapidly with a pressure coefficient of the Curie temperature dT C /dP = -6.3(1) K/GPa. In the Sm-type phase below the Néel temperature of about 100 K (evaluated for 9 GPa), the long range antiferromagnetic order with a propagation vector k AF = (0 0 1/2) is formed. The lattice parameters and unit cell volume as functions of pressure in the hcp and Sm-type phases were determined. A partial phase transformation of the Sm-type phase to the double hexagonal close packed (dhcp) phase was observed at 9 GPa. [ABSTRACT FROM AUTHOR]

The crystal and magnetic structures of the orthoperovskite Pr0.8Na0.2MnO3 with non-integral mean valence (Mn3+/Mn4+) have been studied by means of powder neutron diffraction up to high-quasi-hydrostatic pressure of 4.6 GPa. At normal conditions, the system undergoes a charge ordering transition at TCO=215 K, followed by an antiferromagnetic arrangement of the pseudo-CE type at TN=175 K. Under high external pressures, a microscopically separated state is formed, consisting of a mixture of the A-type AFM phase (TN∼155 K) and metastable FM regions (TC∼175 K). A possible reason for the appearance of the A-type AFM phase is the compression anisotropy which leads to marked apical contraction of MnO6 octahedra under high pressure and creates favorable conditions for appearance of the d(x2−y2) orbital polarization, prerequisite for the A-type AFM order. It is argued that the pressure-induced structural changes in Pr0.8Na0.2MnO3 are accompanied by an insulator–metal transition. [Copyright &y& Elsevier]

• Magnetically disordered phase is suppressed under pressure. • The Néel temperature increases substantially under pressure. • The mechanism of next nearest neighbor superexchange interactions of A-O-O-A type is proposed. The crystal and magnetic structures of the frustrated Co 3 O 4 spinel oxide have been studied by means of neutron diffraction at high pressures up to 8.7 GPa in the temperature range 5–300 K. At ambient pressure, a coexistence of the long range ordered antiferromagnetic (AFM) phase and short range disordered phase below T N = 33 K was observed. At pressures above 2 GPa, a suppression of the magnetically disordered phase and stabilization of the AFM phase, characterized by rapid increase of the Néel temperature in 1.5 times from 33 to 51 K with a pressure coefficient dT N /dP = 2.1 K/GPa occur. The observed phenomena are analyzed in terms of the competing nearest neighbor and next nearest neighbor magnetic interactions. In addition to the A-O-B-O-A nearest neighbor superexchange, an important role of the A-O-O-A next nearest neighbor superexchange interactions in magnetic behavior of Co 3 O 4 is pointed out. [ABSTRACT FROM AUTHOR]

• Structural anomalies at 20 GPa bring indirect evidence of insulator-metal transition. • The Néel temperature of TbBaCo 1.91 Fe 0.09 O 5.5 is reduced substantially under pressure. • The ferromagnetic component of the magnetic structure is suppressed under pressure. • A tendency towards decrease of the ordered Co/Fe magnetic moments is observed. The crystal and magnetic structures of the perovskite-like, oxygen deficient layered cobalt oxide TbBaCo 1.91 Fe 0.09 O 5.5 have been studied by means of neutron diffraction at high pressures up to 6.2 GPa in the temperature range 5–300 K and X-ray diffraction at high pressures up to 30 GPa and ambient temperature. The structural anomalies in lattice compression at P = 20–25 GPa were revealed, which could be associated with the insulator-metal transition. At ambient pressure below T N = 300 K a formation of the complex magnetic structure on the Co/Fe sublattice, comprising the G-type antiferromagnetic (AFM) and ferromagnetic (FM) components, was observed. Below T ≈ 150 K the FM component vanished. At T = 5 K a presence of the long range AFM order on the Tb sublattice was also revealed. At high pressures, the FM component has become suppressed and the only G-type AFM order was found for the Co/Fe sublattice. The Néel temperature decreased noticeably down to 275 K at P = 6.2 GPa with a pressure coefficient dT N / dP = −4 K/GPa. The intrinsic mechanisms of the observed pressure-induced magnetic phenomena are discussed. [ABSTRACT FROM AUTHOR]