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Large thermal hysteresis in the (Mn,Fe)2(P,Si) system hinders an efficient heat exchange and thus limits the magnetocaloric applications. Substitution of manganese by vanadium in the Mn1-x1Vx1Fe0.95P0.593Si0.33B0.077 and Mn1-x2Vx2Fe0.95P0.563Si0.36B0.077 compounds enable a significant reduction in the thermal hysteresis without losing the giant magnetocaloric effect. For the composition closest to the critical one, where first-order crossovers to second-order phase transition in the series of x2 = 0.02, Mn0.98V0.02Fe0.95P0.563Si0.36B0.077 exhibits a thermal hysteresis that is reduced from 1.5 to 0.5 K by 67%, yielding an adiabatic temperature change of 2.3 K and magnetic entropy change of 5.6 J/kgK for an applied field of 1 T, which demonstrates its potential for highly efficient magnetic heat pumps utilizing low-cost permanent magnets.

Magnetite microinclusions in metamorphic harzburgites, derived from the deserpentinization of the subducted hydrated oceanic lithospheric mantle, were examined by synchrotron Mössbauer spectroscopy to investigate the chemical and magnetic environments of the Fe nuclei. The data reveal a critical susceptibility of the octahedral sites of the cubic structure of magnetite to chemical variations, which, in turn, influences their magnetic properties in terms of hyperfine magnetic field intensity and direction. Micromagnetites display substantial remanent magnetization; however, the magnetic moment direction can be significantly different among inclusions, even for those in close spatial proximity. This evidence points to a kinetic control of the composition of microcavities at mantle depths, implying that the use of the remanent magnetic field of included magnetic phases to infer large-scale implications on the Earth's magnetic field requires the development of complex geochemical and geodynamical models.

Spin-Crossover nanomaterials have been actively studied in the past decade for their potential technological applications in sensing, actuating, and information processing devices. Unfortunately, an increasing number of the metallic centers become inactive at reduced sizes, presumably due to surface effects, limiting their switching ability and thus the scope of applications. Here we report on the investigation of "frozen" metallic centers in nanoparticles (2-80 nm size) of the spin-crossover compound Fe(pyrazine)[Ni(CN) 4 ]. Magnetic measurements reveal both high-spin and low-spin residual fractions at atmospheric pressure. A pressure-induced transition of the high-spin residue is observed at around 1.5 GPa by synchrotron Mössbauer spectroscopy. We show that it is equivalent to a downshift of the transition temperature by ca. 400 K due to the size reduction. Unexpectedly, small-angle neutron scattering experiments demonstrate that these high-spin residual centers are not confined to the surface, which contradicts general theoretical considerations.

Polarization analysis of the reflected radiation has been performed in Mossbauer reflectivity measurements with a Synchrotron Mossbauer Source (SMS). Effective pi ->sigma' polarization selection is attained with LiF crystal ((6 2 2) 90 degrees-reflection for 14.4 keV radiation, angular acceptance similar to 100 '') capable of high pi ->pi' suppression. Basic features of the reflectivity with the rotated pi ->sigma' polarization are revealed in the experiment with the [Fe-57(10 ML)/V(20 ML)](20) multilayer. Selection of pi ->sigma' polarization component in Mossbauer reflectivity allows to exclude nonresonant electronic scattering, besides Mossbauer pi ->sigma' reflectivity spectra (R-spectra) contain only contributions from magnetized along the beam ferromagnetic phases. The antiferromagnetic iron oxides do not contribute to pi ->sigma' R-spectra (dichroic component is compensated). Therefore, in the Mossbauer reflectivity experiment supplemented by polarization analysis the data interpretation becomes more certain and gives information about depth position for ferromagnetic layers selectively. With this new technique we locate antiferromagnetic iron phases in the very top layer of [Fe-57(10 ML)/V(20 ML)](20) multilayer and ascertain the ferromagnetic ordered iron layers in the remaining part of the structure. This new approach in Mossbauer reflectivity has interesting perspectives for investigations of hyperfine interactions for iron complexes on the surface, ultrathin layers and multilayers with complicated magnetic structures.

The high pressure structural phase diagram of EuTiO3 is revisited by means of single crystal x-ray diffraction at pressures below 30GPa. We report a transition at about 3GPa with a surprisingly small lattice distortion. At 23GPa we have detected a yet unknown transition into a new orthorhombic phase (space group Ibam). Combining our observations on structures obtained on single crystals and polycrystalline samples with complementary methods, such as electrical resistivity and nuclear forward scattering of synchrotron radiation measured on polycrystalline samples, we address issues relevant to chemistry and disorder.

Mossbauer reflectivity experiment with polarization selection are reported. The use of the LiF polarization analyzer allows us to get the pi ->sigma' peak on the reflectivity curve at the critical angle and Mossbauer pi ->sigma' reflectivity spectra of reasonable quality at the critical angle and also at the Bragg angles of superlattice. The impressive difference of the reflectivity spectra measured near the critical angle with and without polarizations analysis is observed for [Fe-57(10)/V-10](20) multilayer characterizing by the ferromagnetic interlayer coupling. The combined fit of the whole set of spectra measured at different angles reveals the existence of antiferromagnetic Fe oxide phases in the top three bilayers. The experiment demonstrates benefits of the Mossbauer reflectivity with polarization analysis in ultrathin surface layer investigations.

Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mössbauer transition of Ni61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to ∼24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa.

The lattice dynamics in MnFe0.95Si0.50P0.50 were investigated experimentally using Fe57 nuclear inelastic scattering and inelastic x-ray scattering across the first-order magnetic transition which occurs close to room temperature. The lattice dynamics characterization was supported by a macroscopic magnetic characterization, an x-ray diffraction study, and a hyperfine interactions characterization using Mössbauer spectroscopy. The Fe specific and the x-ray generalized density of phonon states were obtained both in the ferromagnetic and in the paramagnetic state. A prominent shift, 2meV at 20meV, in the x-ray generalized density of phonon states across the first-order magnetic transition, that involves vibrations with essentially Fe character, is revealed corroborated by a change in the local environment quantified in the isomer shift and the quadrupole splitting. Above 35meV the vibrational modes are practically insensitive to the magnetic transition. The entropy change induced by a 1T magnetic field across the magnetic transition, ∼10J/K/kg, is only a fraction of the Fe vibrational entropy change, 62(21)J/K/kg., RST/Fundamental Aspects of Materials and Energy

The assembly of a Lock-In digital Amplifier (LIdA) from widely accessible ready-made modules is presented. This equipment, which does not require any advanced knowledge of electronics or programming, may introduce the experimenter to resonant techniques by registering mechanical resonances. The freely available control program allows for general data acquisition and further data processing. The apparatus is versatile and may corroborate the science and engineering laboratory in elasticity measurements or in a series of experiments where a modulated signal is a prerequisite., Accepted Author Manuscript, RST/Fundamental Aspects of Materials and Energy

Magnetic properties of NiO have been studied in the multimegabar pressure range by nuclear forward scattering of synchrotron radiation using the 67.4 keV Mossbauer transition of Ni-61. The observed magnetic hyperfine splitting confirms the antiferromagnetic state of NiO up to 280 GPa, the highest pressure where magnetism has been observed so far, in any material. Remarkably, the hyperfine field increases from 8.47 T at ambient pressure to similar to 24 T at the highest pressure, ruling out the possibility of a magnetic collapse. A joint x-ray diffraction and extended x-ray-absorption fine structure investigation reveals that NiO remains in a distorted sodium chloride structure in the entire studied pressure range. Ab initio calculations support the experimental observations, and further indicate a complete absence of Mott transition in NiO up to at least 280 GPa., Funding Agencies|National Science Foundation-Earth Sciences [EAR-1128799]; Department of Energy-GeoSciences [DE-FG02-94ER14466]; DOE Office of Science [DE-AC02-06CH11357]; Helmholtz Association; Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy; Swedish Government Strategic Research Area Grants Swedish e-Science Research Center (SeRC) and in Materials Science on Functional Materials at Linkoping University [2009 00971]; Knut and Alice Wallenbergs Foundation project Strong Field Physics and New States of Matter; Swedish Foundation for Strategic Research program SRL Grant [10-0026]; Swedish Research Council (VR) [2015-04391]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D.I. Mendeleev Fund Program