Elastic diffuse scattering of neutrons was found around various Bragg-peak positions in FeNi Invar alloys. The diffuse scattering intensities depend on the temperature and Ni concentration. The intensities increase with decreasing temperature and decrease with increasing Ni concentration. The distribution of diffuse scattering intensity changes from peak to peak and is well explained by the formation of clusters with a lattice deformation consisting of a shear wave propagating along the < 1 1 0 > direction and with the < 1 - 1 0 > polarization vector. The ranges of temperature and Ni concentration, for which diffuse scattering is observed, coincide with those for which the Invar anomalies are observable. The origin of the clusters together with the lattice deformation and their role with regard to the Invar effects are discussed as well as the possibility of a precursor for the fcc-bcc martensitic transformation observed in FeNi alloys.

A kink was observed near 20 kOe in the field dependence of the magnetization in a single-grained α-Mn without a magnetic hysteresis below the Neel temperature in an accurate magnetization measurement below 80 kOe. It was observed along [1 0 0], [1 1 0] and [1 1 1] crystallographic directions. The field dependence of the magnetization above 40 kOe extrapolates to positive finite magnetization at null field. The kink suggests a weak metamagnetism induced by the external magnetic field. A small but clear anisotropy was observed between the weak-field susceptibilities along [1 0 0] and [1 1 0]/[1 1 1] directions. A previously reported large susceptibility anomaly was not affirmed between 90 and 270 kOe. © 2008 Elsevier B.V. All rights reserved.

Magnetism of simple cubic antiferromagnet Pt3Fe alloy was studied by neutron scattering under uniaxtial pressure. NW temperature while relative intensity of the (1)/(1)(2)/(2)0 Bragg peak at the low-temperature phase decreased under the uniaxial pressure. Actual nonincreased, collinear magnetic structure model at the low-temperature phase was proposed under the reasonable assumption. (c) 2006 Elsevier B.V. All rights reserved.

To determine the exchange coupling constants between spins, magnon dispersion relation in FePt alloy was studied by neutron inelastic scattering measurements. Data analysis based on the localized spin model led to the result that magnetic moments of Pt atoms couple with those of Fe atoms anti-parallel. Powder diffraction measurements were also performed to determine the sizes and the direction of magnetic moments of Fe and Pt atoms. The results were 1.93 and -0.49 mu(B) for Fe and Pt, respectively. The results are consistent with those of magnon dispersion relation. (c) 2006 Elsevier B.V. All rights reserved.

Strong inelastic scattering of neutrons extends along the first Brillouin zone boundary of FCC structure on Mn73Cu27 alloy at room temperature, indicating that Mn spins fluctuate dynamically with strong spin correlations. The fluctuation is considered to be caused by geometrical spin frustration of the octahedral antiferromagnet and suppresses the magnetic LRO. At low temperature, part of spins freezes due to the randomness of atomic arrangements, resulting in spin-glass-like behavior. (c) 2006 Elsevier B.V. All rights reserved.

The phonon dispersion relations for tetragonal PbTiO3 have been determined along the [100], [110], and [001] directions at room temperature by inelastic neutron scattering. The zone-boundary TA phonon energies for PbTiO3 are considerably lower than those for BaTiO3 and SrTiO3, indicating the dominant role of Pb atoms in TA phonons. The zone-center TO-A(1) phonon energy is higher than the zone-center TO-E phonon energy. A preliminary high-temperature experiment has revealed the gradual softening of the TO-A(1) phonons and the stability of TO-E phonons up to 643 K (0.84 T-c). The TO-A(1) phonons have an extremely broad linewidth, in marked contrast to the well-defined TO-E phonons. The TO phonons at the zone-boundary M point indicate that the energy for the rotational mode of the oxygen octahedra is approximately half of that for the distortion of the octahedra along the c axis. The X-point TO phonon energies for PbTiO3 are much higher than those for Pb(Zn1/3Nb2/3)O-3, suggesting that the B-site atoms in ABO(3) contribute largely to the TO phonons in Pb-based perovskites. Present phonon dispersion relations are generally in agreement with the first-principles calculations for the zone-center and zone-boundary phonon energies.

The phonon density of states of a pseudomorphic fcc-Fe film with similar to 3 monolayers has been investigated by nuclear resonant inelastic scattering. The fcc-Fe layers are intercalated into an interface between monolayer hexagonal boron nitride and a Ni(111) substrate with a commensurate relation. The in-plane nearest-neighbor distance of the fcc-Fe film is shorter than that of uncompressed fcc-Fe precipitates in Cu by -1.8%. The compression increases the mean force constant of the fcc-Fe film, which is higher than that of uncompressed fcc-Fe precipitates by 5.8%.

It is common knowledge that the magnetic structure of fcc Fe (gamma-Fe) can be described by means of an incommensurate spin-density wave (SDW). Previous experimental data, however, were mostly obtained for gamma-FeCo alloy precipitates in Cu in order to avoid the complexity of the structural phase transition. Since Fe is a fundamental element, reliable data on the SDW state for pure gamma-Fe are highly desired. We present here neutron scattering data for the SDW in pure gamma-Fe precipitates in Cu and discuss the particle size effect of the SDW.

Magnetic properties of ZnFe2O4 were studied for various specimens prepared by different thermal and artificial treatments using neutron scattering, Mossbauer spectroscopy and DC and AC susceptibilities. We found a strong correlation between the magnetic Bragg peak intensity and the Mossbauer absorption line-width. Comparing with the susceptibility data, it is discussed what are the intrinsic magnetic properties of ZnFe2O4 as a typical 3-D geometrical spin frustration system.

Using inelastic neutron scattering, we measured the diffuse scattering pattern of the geometrically frustrated 110CdFe2O 4. The observed pattern resembles that of ZnCr2O 4, indicative of strong nearest-neighbor antiferromagnetic correlations in contrast to the ferromagnetic nearest neighbor interactions of the isomorphic ZnFe2O4. This result demonstrates that the subtle 90° Fe3+-O-Fe3+ interaction changes its nature by chemical pressure. Meanwhile, the temperature dependence of the diffuse scattering shows hexagonal spin objects decay very gradually with increasing temperature and can be seen even at temperature as high as five times Curie-Weiss temperature. At low temperatures, spin freezing with only short-range correlations is observed associated with 13 K susceptibility anomaly. No long-range order is found down to 0.1 K with applied field of up to 9 T.

Tetragonal lattice distortion of the PtFe alloy was studied by neutron diffraction as a function of temperature. The tetragonality (1 - c/a) increases with increasing temperature up to the Curie temperature (T-C = 750 K). Data analysis based on the hard sphere model in the (1 1 1) plane leads to the shrink of the atomic volume of Fe with increasing temperature. The invar-like effect at high temperature would exert a significant influence on the magnetic anisotropy energy of this system. (C) 2004 Elsevier B.V. All rights reserved.

Mn3Pt alloy has a special magnetic structure, which is considered that one third of Mn atoms have no magnetic moment. We found that the lattice slightly distorts to a tetragonal structure and our neutron scattering data in the F-phase show inelastic diffuse scattering located along the first Brillouin zone boundary of the FCC-structure, indicating that the one third of Mn spins fluctuate dynamically with strong correlations. The Mn3Pt alloy has a partial spin frustration. Coexistence of static collinear spin structure and dynamical spins in the F-phase is a characteristic of the ordered Mn3Pt alloy. (C) 2003 Elsevier B.V. All rights reserved.

A new spin frustration system with an octahedral configuration of magnetic atoms was found. In neutron scattering measurements for an ordered Mn3Pt alloy, inelastic diffuse scattering intensity distributes along the first Brillouin zone-boundary of the fee structure in the paramagnetic and the F-phases. Within the calculations based on a RPA, the experimental data in the paramagnetic phase are reproduced using antiferromagnetic couplings between the spins up to the third-neighbor exchange interactions. In the F-phase below the Neel temperature, a part of the Mn spins still fluctuates at the special site. The existence of the F-phase is a characteristic of the octahedral spin frustration system. The effects of the chemical disorder on the spin frustration are also studied using a specimen with a small atomic LRO parameter.

Magnetic structures of Pt100-XFeX (X = 16, 18, 24 and 25) alloys were studied by means of neutron elastic and inelastic scattering. Non-collinear antiferromagnetic structure is experimentally verified for the ground state of the stoichiometric alloy Pt3Fe. The antiferromagnetic phase transition below T-N in Pt3Fe alloy is considered to be one of the crossover points of the antiferromagnetic spin correlations which show successive change towards the original point of the reciprocal lattice with increasing Fe concentration in the wide concentration range of the Pt-Fe system.

The atomic short range order of Pd-Ti and Pt-Ti alloys with a Ti concentration of about 10 at.% was studied by neutron diffraction. Temperature-independent diffuse satellite peaks were observed at incommensurate positions on the [100] axis. Due to the various properties of the diffuse satellite peaks, a concentration wave of constituent atoms appeared as a reflection of the special shape of the Fermi surfaces of the alloys. Its relationship to the Pt8Ti superlattice structure is discussed.

The phonon density of states of gamma-Fe precipitates in a Cu matrix were studied as a function of particle size by using nuclear resonant inelastic scattering of synchrotron radiation. The host metal affects the phonon density of states of the precipitates up to 30 nm in diameter. Larger precipitates are free from the influence of the host metal and show rather similar phonon density of states to those of fcc-Fe alloy bulk specimens such as stainless steel (310ss) and Fe70Ni30 at room temperature although gamma-Fe is unstable at room temperature under an atmospheric condition. Careful observation, however, yields characteristics of gamma-Fe precipitates in the phonon density of states.

Mössbauer spectra of a single crystal of LuFeCoO4 are studied in the temperature range between 4.2 K and 70 K. The Mössbauer spectra are separated into two components. We propose a model that one of three spins in a spin plane is parallel to the c-axis and other two orient to 120 to the c-axis. This model explains the experimental data satisfactory. It is concluded that the spins parallel to the c-axis are more stable than the other when temperature is increased. The Ising like character observed in susceptibility measurements can be explained by this spin arrangement in the spin planes.

Atomic short-range order and magnetism in Pt1-xCrx alloys with x=0.07, 0.10, 0.13, and 0.16 were studied by means of neutron scattering and susceptibility measurements. The latter showed a spin-glass-type anomaly at low temperature for x=0.13 and 0.16, but a monotonic increase towards the lowest temperature for x =0.07 and 0.10. In neutron scattering, broad satellite peaks with asymmetric intensities were observed for all specimens along the [1 0 0] direction, even at room temperature. These peaks are well explained as a concentration wave of constituent atoms accompanied with a periodic lattice deformation. Magnetic diffuse scattering was observed for the specimens with x=0.13 and 0.16. The origin of the spin-glass-like behavior in these alloys is ascribed to the dynamics and freezing of spin-density-wave cluster fluctuations, similar to the case of CuMn spin-glass alloys. A breakdown of the Kondo singlet state was studied for an x= 0.10 nonmagnetic alloy using neutron scattering under a magnetic field of 6 T.

Pt-V alloys with V concentrations of 7, 10, 13, and 19 at.% were studied by neutron scattering. Although an equilibrium atomic long-range order has not been reported in these concentration ranges, we observed diffuse satellite peaks around the 1+/-delta,0,0 positions at room temperature. These satellite peak positions depend on the V concentration and are incommensurate with the lattice periodicity. The diffuse satellite peaks can be explained by an atomic concentration wave, in which the impurity atoms are coupled through oscillating screening charges. Thus, the concentration wave reflects the shape of the Fermi surfaces in the Pt alloys. In order to confirm the Fermi surface effect, Pd-V alloys with V concentrations of 10, 11.5, and 13 at.% were also studied because the Fermi surfaces of Pd are very similar to those of Pt. Diffuse satellite peaks around the 100 reciprocal lattice point were again observed at room temperature in the Pd-V alloys, supporting the idea that these concentration waves are reflections of the special shape of Pt and Pd Fermi surfaces.

Due to a special shape of Fermi surfaces in Pd and Pt metals, charge and magnetic impurity potentials induce the oscillatory shielding with large amplitude and extending to long distance along the [100] direction. As a result, Pd-M and Pt-M (M = Ti, V, Cr, Mn, Fe and Co) alloys show short range order of different types, but with the same symmetry. These are an atomic concentration wave for non-magnetic alloys (M = Ti, V, Cr), a spin-density-wave for spin-glass alloys (M = Cr, Mn) and a transverse spin modulation wave for ferromagnetic alloys (M = Fe, Co) .