Weissenberg-type neutron diffraction camera and its application to the structural and magnetic phase transitions of KMnF3

Watanabe, Shinji; Yoshimura, M.; Hidaka, M.; Yoshizawa, H.

doi:10.1007/s00339-006-3599-8

Cited by 3 publications

(7 citation statements)

References 17 publications

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“…At this temperature, characteristic of a first-order phase transition, an abrupt jump and a large hysteresis of approximately 2 K appear in various measurements. 21,30,34,37 These results are consistent with the neutron diffraction measurements, 36 which demonstrate that this transition is structurally of the first order and magnetically of the second order.…”

Section: Introductionsupporting

confidence: 88%

“…Three structural phase transitions were observed at 186.5, 88, and 82 K through x-ray diffraction 34 and at 185, 90, and 83 K through neutron diffraction. 36 Furthermore, three anomalies associated with phase transitions at 186.2, 86.6, and 80.5 K were reported through thermal measurements. 37 The first transition occurs at T c1 = 186 K and corresponds to the softening of the R zone-boundary mode located at the R(1/2,1/2,1/2) corner of the cubic Brillouin zone.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast dynamics of soft phonon modes in perovskite dielectrics observed by coherent phonon spectroscopy

et al. 2011

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Coherent phonons were observed in perovskite dielectrics LaAlO 3 and KMnF 3 using ultrafast polarization spectroscopy. Ultrafast dynamics and softening of phonon modes, which contribute to structural phase transitions, were studied. The temperature dependences of the phonon frequency and relaxation rate were obtained from the observed damped oscillation of coherent phonons. In LaAlO 3 , typical softening of the phonon frequency was observed toward the phase-transition temperature T c (∼ 750 K). The observed relaxation for the soft-mode phonons is explained well by a population decay due to anharmonic phonon-phonon coupling. In KMnF 3 , two structural phase-transition temperatures, T c1 (= 187 K) and T cm (∼ 81 K), were found through birefringence measurement. At temperatures below T cm , three modes of coherent phonons were observed and the phonon modes were found to undergo softening toward T cm . The observed dependences of the coherent phonon signal on the pumping polarization and the temperature suggest an orthorhombic structure, instead of a monoclinic structure, at temperatures below T cm . The sudden decrease in the phonon frequency at T cm indicates the first-order character of the phase transition at T cm . Notable changes in birefringence and phonon frequency were observed at around 90 K, but no distinct anomaly is found, which suggests that the structure undergoes continuous change. Above 100 K, the E g mode in the tetragonal symmetry is found to undergo softening toward T c1 . A coherent phonon signal of relaxation type appears at around T c1 and survives even at near room temperature, which suggests the existence of structural disorder even in the cubic symmetry above T c1 .

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Section: Introductionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Ultrafast dynamics of soft phonon modes in perovskite dielectrics observed by coherent phonon spectroscopy

et al. 2011

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“…T n2 values are essentially the same (81, 82, and 83 K) in almost all the published data (Table I), with the same characteristic hysteresis of 1 to 2 K between heating and cooling as observed in measurements of structural properties (e.g., Refs. 12,16,21,22,25,28,29,and 33). There seems to be no doubt that this is coincident with the III → IV transition (T n2 = T c3 ), and the transition temperatures from both magnetic and structural measurements are therefore listed simply under T c3 in Table I.…”

Section: Sourcementioning

confidence: 93%

“…5 Hidaka et al (1975) 25 81 88 91 Benard and Walker (1976) 26 80 89 184 Holt and Fossheim (1981) 27 187. 2 Stokka et al (1981) 4 186.9 Sakashita et al (1981) 5 186.7 28 83/84 87.7 ± 0.1 95 188 Hidaka et al (1986) 29 83 88 88 Hidaka et al (1989) 30 83 92 83 88.0 Sakashita et al (1990) 6 186 * Gibaud et al (1991) 1 82 88 186.5 Ratuszna and Kachel (1992) 31 91 186 Kapusta et al (1999) 32 96 195 * Hayward et al (2000) 11 186.0 Watanabe et al (2006) 33 81-84 Salazar et al (2007) 34 79. 35 91.0 186.7 * Salje et al (2009) 36 186.0 * Salje and Zhang (2009) 37 184 Kizhaev and Markova (2011) 38 82 phase IV as it is the typical low-temperature structure of most perovskites with both Rand M-point tilting, including NaMnF 3 and NH 4 MnF 3 for example.…”

Section: Sourcementioning

confidence: 99%

“…The space groups of phases III and IV have not been determined, but single-crystal diffraction patterns from phase III reveal the presence of both R-point and M-point reflections. 1,2,29,30,33 Thus, it appears that phase II arises by condensation of an R-point soft mode and phase III by condensation of an M-point soft mode, 2,39,40 in the classical manner of octahedral tilting transitions in perovskites. In some diffraction data the II → III transition looks first order (Table I).…”

Section: Introductionmentioning

confidence: 99%

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Magnetoelastic coupling and multiferroic ferroelastic/magnetic phase transitions in the perovskite KMnF3

2012

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The magnetic, elastic, and anelastic behavior of single-crystal KMnF 3 have been investigated by superconducting quantum interference device (SQUID) magnetometry and resonant ultrasound spectroscopy (RUS) through the sequence of phase transitions: phase I, P m3m → (T c1 = 185 K) → phase II, I 4/mcm → (T c2 = T N = 87 K) → phase III, antiferromagnetic, Cmcm → (T c3 = 82 K) → phase IV, canted ferromagnet, Pnma. It is concluded that observed changes in the elastic properties can be explained simply in terms of strain/order parameter coupling for the octahedral tilting transitions. There appears to be no evidence in the present data or in data from the literature for coupling between the magnetic order parameter and shear strains. Any coupling between the magnetic and structural transitions is therefore weak, probably occurring only biquadratically through a small common volume strain. The combined data show unambiguously that, for the crystal used, the Néel point and the structural transition at 87 K are coincident. In other crystals, with slightly different stoichiometries and defect contents, this need not be the case, however, and the overlap of transition temperatures in KMnF 3 is essentially accidental. Strong acoustic dissipation at ∼0.1-1 MHz in the stability field of phase II is attributed to the local mobility of transformation twin walls under externally applied stress. A Debye-like loss peak near 130 K is attributed to pinning of at least some twin walls by defects, but relatively high levels of acoustic dissipation below this freezing temperature imply that some of the twin walls remain mobile due to weak pinning or the absence of any pinning. Acoustic losses continue in the stability field of phase III (Cmcm) but diminish substantially in the stability field of phase IV (Pnma), implying quite different twin mobilities in the different structure types. Overlap of the structural and magnetic instabilities in KMnF 3 opens up possibilities for manipulation of ferroelastic twinning by application of a magnetic field and for creation of materials in which the ferroelastic twin walls have quite different magnetic properties from the matrix in which they lie.

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Critical behavior of the thermal properties ofKMnF3

et al. 2007

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An ac photopyroelectric calorimeter has been used to measure simultaneously the specific heat, thermal conductivity and thermal diffusivity around the antiferromagnetic to paramagnetic phase transition in KMnF 3 . It has been found that the critical exponent and the amplitude ratio of the thermal diffusivity are the same as those of the specific heat. Both values agree with the predictions of the three-dimensional Heisenberg model for isotropic magnets, although this transition is not only magnetic but structural as well. The thermal conductivity shows a broad peak at the Néel temperature that could be related to a reduction of the phonon scattering by the spin fluctuation as the transition temperature is approached.

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Weissenberg-type neutron diffraction camera and its application to the structural and magnetic phase transitions of KMnF3

Cited by 3 publications

References 17 publications

Ultrafast dynamics of soft phonon modes in perovskite dielectrics observed by coherent phonon spectroscopy

Ultrafast dynamics of soft phonon modes in perovskite dielectrics observed by coherent phonon spectroscopy

Magnetoelastic coupling and multiferroic ferroelastic/magnetic phase transitions in the perovskite KMnF3

Critical behavior of the thermal properties ofKMnF3

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