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A monoclinic Y0.7Er0.3Fe2D4.2 compound exhibits unusual magnetic properties with different field induced magnetic transitions. The deuteride is ferrimagnetic at low temperature, and the Er and Fe sublattices present magnetic transitions at different temperatures. The Er moments are ordered below TEr = 55 K, whereas the Fe moments remain ferromagnetically coupled up to TM0 = 66 K. At TM0, the Fe moments display a sharp ferromagnetic–antiferromagnetic transition (FM–AFM) through itinerant electron metamagnetic behavior very sensitive to any volume change. Y0.7Er0.3Fe2D4.2 becomes paramagnetic above TN = 125 K. The pressure dependence of TEr and TM0 has been extracted from magnetic measurements under hydrostatic pressure up to 0.49 GPa. Both temperatures decrease linearly upon applied pressure with dTEr/dP = −126 and dTM0/dP = −140 K GPa−1 for a field of B = 0.03 T. Both magnetic Er and ferromagnetic Fe orders disappear at P = 0.44(4) GPa. However, under a larger applied field B = 5 T, dTM0/dP = −156 K GPa−1, whereas dTEr/dP = −134 K GPa−1 showing weaker sensitivity to pressure and magnetic field. At 2 K, the decrease of the saturation magnetization under pressure can be attributed to a reduction of the mean Er moment due to canting and/or a crystal field effect. Above TM0, the magnetization curves display metamagnetic behavior from an AFM to FM state, which is also very sensitive to the applied pressure. The transition field Btrans, which increases linearly upon heating, is shifted to a lower temperature upon applied pressure with ΔT = −17 K between 0 and 0.11 GPa. These results show strong decoupling of the Er and Fe magnetic sublattices vs temperature, applied field, and pressure. [ABSTRACT FROM AUTHOR]

A versatile type of non-magnetic uniaxial pressure cell has been designed for magnetic measurements in SQUID magnetometer. An advanced technology of machining of miniature parts of the cell was used to make new type of an internal squeezer module, where a sample can be compressed by force up to 3 kN in direction perpendicular to external magnetic field. A correct operation of the cell was tested by study of magnetic behaviour of the Heusler off-stoichiometric Ni2MnSn alloy under uniaxial compression. An unexpected significant difference between reversible effects of uniaxial compression on magnetization of the austenite and martensite phases of the alloy is discussed. The uniaxial compression effects are compared with the effects of hydrostatic pressure on a coupling between magnetization and structural transformation of the alloy. [ABSTRACT FROM AUTHOR]

Substitution of Mn for Fe in Ce2Fe17 strongly suppresses the ferromagnetic ground state, changing it into an antiferromagnetic one. However, a state of spontaneous magnetization is re-entered in the Ce2Fe17-xMnx compounds when the Mn content reaches x=1.3. Magnetic structures and magnetic interactions in the re-entrant ferromagnetic Ce2Fe15.3Mn1.7 compound have been studied using both microscopic (neutron powder diffraction in magnetic fields of up to 0.7 T) and macroscopic (ac susceptibility and magnetization measurements under high pressures of up to 8 kbar in magnetic fields of up to 5 T) techniques. A spiral magnetic structure distorted by the presence of an in-plane ferromagnetic component is found below TN=182 K. Enhancement of the ferromagnetic interactions leads to a steep transformation of the magnetic spiral to a magnetic structure with nonzero spontaneous magnetization below ΘT=59 K. This structure is described by a distorted elliptical spiral model with an incommensurate propagation vector along the c axis. Magnetic field significantly expands the range of stability of this re-entrant ferromagnetic phase. In contrast to the magnetic field, application of pressure does not change ΘT within the achieved pressure range. It leads to a moderate reduction of the Néel temperature, dTN/dP=-2.3 K/kbar. The preferential placement of Mn on some crystallographic sites in Ce2Fe17-xMnx and the related changes of volume and internal magnetic field will be discussed as possible reasons of the peculiar magnetic behavior of this compound. [ABSTRACT FROM AUTHOR]

Substitution of Mn for Fe in Ce2Fe17 strongly suppresses the ferromagnetic ground state, changing it into an antiferromagnetic one. However, a state of spontaneous magnetization is re-entered in the Ce2Fe17-xMnx compounds when the Mn content reaches x=1.3. Magnetic structures and magnetic interactions in the re-entrant ferromagnetic Ce2Fe15.3Mn1.7 compound have been studied using both microscopic (neutron powder diffraction in magnetic fields of up to 0.7 T) and macroscopic (ac susceptibility and magnetization measurements under high pressures of up to 8 kbar in magnetic fields of up to 5 T) techniques. A spiral magnetic structure distorted by the presence of an in-plane ferromagnetic component is found below TN=182 K. Enhancement of the ferromagnetic interactions leads to a steep transformation of the magnetic spiral to a magnetic structure with nonzero spontaneous magnetization below ΘT=59 K. This structure is described by a distorted elliptical spiral model with an incommensurate propagation vector along the c axis. Magnetic field significantly expands the range of stability of this re-entrant ferromagnetic phase. In contrast to the magnetic field, application of pressure does not change ΘT within the achieved pressure range. It leads to a moderate reduction of the Néel temperature, dTN/dP=-2.3 K/kbar. The preferential placement of Mn on some crystallographic sites in Ce2Fe17-xMnx and the related changes of volume and internal magnetic field will be discussed as possible reasons of the peculiar magnetic behavior of this compound. [ABSTRACT FROM AUTHOR]

Linear thermal expansion and magnetostriction measurements under a magnetic field up to 20 kOe, applied parallel and perpendicular to the measuring direction and in the temperature range of 10-300 K, have been performed on a Ni[sub 2]MnGa polycrystal. The effects of zero-field cooling and field cooling on both the self-strain (H=0) and the magnetic-field-induced strain (MFIS) have been studied. We have found that the MFIS strongly depends on whether a magnetic field was applied during the cooling process. The applied magnetic field facilitates the growth of specific orientation variants along the field direction as the sample is cooled down through martensitic transformation. However, the application of a field in the martensitic phase induces a negligible motion of twin boundaries. On this basis, the singular point detection technique performed on polycrystalline specimens results in being the easiest and most direct way by which to determine the anisotropy field in this class of materials. The temperature behavior of the anisotropy constant and field has been determined for Ni[sub 2]MnGa. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highlights • Effect of volume change on anisotropy. • Spin reorientation transition. • High volume stability of the magnetic properties. • Moderate decrease of the Curie temperature with increasing pressure. Abstract The magnetic properties of HoCo 12 B 6 ferrimagnetic compound are investigated versus the magnetic field, temperature and pressure. The magnetic phase diagram exhibits three remarkable temperatures: the ordering temperature T C , the spin reorientation temperature T SR and the compensation temperature T COMP at 147 K, 76 K and 47 K respectively. In HoCo 12 B 6 intermetallic system the spontaneous magnetization resulting from the antiparallel coupling of the magnetic moments of Ho and Co sublattices is pressure insensitive at lowest temperatures whereas it decreases with pressure at temperature range above T SR. The mean Co magnetic moment is small (<0.5 µ B) in the studied compound and exhibits a weak pressure dependence. In addition, significant pressure effects have been observed on both the spin reorientation transition and the Curie temperatures. A value of dT C /dp = −3.5 ± 0.4 K GPa−1 is dominated by the Co sublattice contribution. The spin reorientation transition temperature is also found to decrease versus pressure dT SR /dp = −4.2 ± 0.4 K GPa−1. The compensation temperature where the Ho and Co sublattices have the same magnitude but opposite direction does not vary significantly with applied pressure in the investigated pressure range (up to 1 GPa). The results of pressure dependence of the magnetic properties are compared to earlier results on other R-Co-B borides. HoCo 12 B 6 compound confirmed the remarkably high volume stability of the magnetic properties of the RCo 12 B 6 compounds with the itinerant character of magnetism and low values of both the T C and magnetization. [ABSTRACT FROM AUTHOR]

A system for direct measurements of the magneto-caloric effect (MCE) exploits a rapid transport of a sample into or from magnetic field in permanent Halbach-type (1 T) or superconducting (4.7 T) magnets. Time dependence of induced changes of the sample temperature, ΔT(t), is detected directly by the differential Cu-Constantan-Cu micro-thermocouples with time steps of 300 ms. A sample placed inside an evacuated simple LN2 cryostat is either totally isolated (adiabatic conditions) or partly connected with the copper sample holder (non-adiabatic conditions). The last arrangement (a model of the Brayton cycle) is used to simulate an application of MCE in refrigeration techniques. The relations describing ΔT(t) that allow an analysis of MCE of the studied materials are based on the general cooling law. The effect of the first-order magnetic transition on MCE of selected sample is also demonstrated by non-standard ΔT(t) curves measured in the last mentioned experimental arrangements. [ABSTRACT FROM AUTHOR]

Two miniature uniaxial high-pressure CuBe cells have been designed for magnetic and neutron-diffraction studies of single crystals in a SQUID magnetometer and in a neutron diffractometer, respectively. Uniaxial elastic compression can be applied along or crosswise of the magnetic field direction or the diffractometer axis. Oriented single crystals are smoothly squeezed-up to a sample yield stress by a force of up to 20 kN produced by Bellville springs. The cell was successfully used for the study of huge anisotropy of magnetic interactions in the NdRhSn single crystal. [ABSTRACT FROM AUTHOR]

Abstract: The experimental study of the pressure effect on magnetization and compensation temperature of ferrimagnetic GdCo2Fe2B in a magnetic field up to 7 T under hydrostatic pressures up to 10 kbar is presented. Due to the mutual antiparallel arrangement of Gd and 3d sublattices and the negligible pressure effect on localized Gd magnetic moment, the observed increase of with pressure can be attributed to the pressure induced decrease of 3d magnetic moments, predominately to the decrease of Fe moment, . The pressure induced increase of is also responsible for the remarkable increase of under pressure . This opens the field to tunablibilty of the . [ABSTRACT FROM AUTHOR]

We report a study of the effect of hydrostatic pressure on the magnetocaloric effect in a La0.69Ca0.31MnO3 single crystal. The single crystal exhibits a much larger magnetic entropy change (ΔSm) than the corresponding polycrystalline samples, reaching 5.2 J/kg K and 8.5 J/kg K for a magnetic field variation of 1 T and 5 T, respectively. Under hydrostatic pressure, the peak position of ΔSm significantly moves to higher temperatures due to the shift of the magnetic phase transition, from 213.5 K under ambient pressure up to 236.5 K under a pressure of 1.1 GPa, while the maximum value of ΔSm remains nearly the same. These exceptional results demonstrate that the magnetocaloric effect in magnetic materials with strong spin-lattice coupling can be effectively tuned by pressure. [ABSTRACT FROM AUTHOR]

Pulsed magnetic fields up to 68 Tesla have been used to determine the intersublattice coupling strength and its temperature dependence of GdCo12B6 compound. This compound exhibits ferrimagnetic behaviour below 163 ± 2 K. Two antiferromagnetically coupled sublattices cancel out at compensation temperature at about 48 K. They are carrying magnetization of typically 0.42 μB/Co atom and 7 μB/Gd. The intrinsic magnetic properties of the GdCo12B6 compound have been determined by combining low temperature magnetic measurements in both steady and pulsed magnetic field, as well as isofield studies in steady field. At 4.2 K, the magnetization curve of GdCo12B6 is found to reach the full saturation with sum of both sublattice magnetizations for an applied magnetic field of about 68 T. In addition a detailed study is presented in the whole ordered temperature range on the basis of magnetization curves recorded using pulsed magnetic field up to 60 T. This has enabled to investigate the intersublattice coupling strength and its temperature dependence, a value JCo-Gd/kB = -5.3 ± 0.3 K is derived from the magnetization curves whereas one gets much larger value for JCo-Co/kB = 108 K. [ABSTRACT FROM AUTHOR]

The magnetic properties of polycrystalline Lu2Fe16.5Mn0.5 and Lu2Fe16.3Mn0.7 compounds have been studied under hydrostatic pressure up to 10 kbar in the temperature range of 5-300 K and at magnetic fields up to 5 T. The Lu2Fe16.3Mn0.7 compound is in the ferromagnetic (FM) state, and the Lu2Fe16.5Mn0.5 is in the FM state at low temperatures and in the antiferromagnetic state at high temperatures at ambient pressure. We have revealed that the FM state is very sensitive to volume changes and even moderate pressure is sufficient to complete its suppression. The critical pressures are 4 kbar for Lu2Fe16.5Mn0.5 and 7 kbar for Lu2Fe16.3Mn0.7. The suppression of the FM ground state is observed at practically the same volume of the elementary cell. The pressure induced Néel temperature, TN, of both compounds decreases with increasing pressure, dTN/dp = -2.5 K/kbar and dTN/dp = -3.4 K/kbar, for Lu2Fe16.5Mn0.5 and Lu2Fe16.3Mn0.7, respectively. The remarkable strengthening of the FM ground state by the Mn substitution and its total suppression by external pressure can mainly be attributed to a subtle competition of positive and negative local direct exchange interactions between Fe atoms located at inequivalent structural sites. These interactions are strongly dependent on the interatomic Fe-Fe distances. [ABSTRACT FROM AUTHOR]

Effect of pressure on magnetic properties of a bulk fluoro-metal complex (NH3OH)2MF4 was studied. Magnetization measurements suggest that a ferromagnetic transition at TC1 = 47 K is followed by a ferrimagnetic one at TC2 = 3 K. Both transition temperatures are pressure dependent with the pressure coefficients dTC1/ dp = - 2.6 K/GPa and dTC2/ dp = 0.26 K/GPa. The opposite sign of the coefficients is an additional indication of a different nature (ferromagnetic/antiferromagnetic) of these two transitions. The effect of pressure on low field magnetization and exchange bias phenomena is small but still visible. [ABSTRACT FROM AUTHOR]

The effect of external hydrostatic pressure on magnetic properties is studied for the UCo 0.995 Os 0.005 Al single crystal. At ambient pressure, the ground state is ferromagnetic. Even lowest applied pressure 0.11 GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition is observed only in magnetic fields along the c axis of the crystal, similar to previously studied itinerant electron metamagnet UCoAl. Temperature dependence of the susceptibility for various pressures shows a broad maximum at T max ~ 20 K. The experimental data are analyzed with the theory of itinerant electron metamagnetism, which considers anisotropic thermal fluctuations of the uranium magnetic moment. The observed pressure dependence of the susceptibility at T max and the temperature for the disappearance of the first-order metamagnetic transition are explained with the theory. [ABSTRACT FROM AUTHOR]

The atomic and magnetic structures of Ce[sub 2]Fe[sub 17-x]Mn[sub x] compounds with x = 0.5 and 1.0 were investigated using neutron diffraction under magnetic fields up to 5.0 T over the temperature range 2-300 K. The magnetic reflexes observed at temperatures 2-208 K and µ[sub 0] H = 0 T correspond to an incommensurate antiferromagnetic structure with wave vector [0, 0, 0 ± τ] at 2 K. This structure is suppressed in an external magnetic field and a ferromagnetic phase is induced in fields higher than 0.6 T. The complex transformation of the magnetic structures under magnetic field and temperature is analyzed and discussed. [ABSTRACT FROM AUTHOR]

investigation of properties of powders of the Heusler Ni 2 MnSn-based alloys revealed the extreme suppression of both, the magnetization and the exchange-bias and exchange spring effects in powders of the alloys. Furthermore, the structural transformation between austenite and martensite phases of the alloys is hindered in the powders, hysteresis curves do not exhibit saturation and observed cluster-glass behavior of the powders at low temperature is almost independent on magnetic field and on composition of the alloys. A complex conjunction of exchange-bias effect and frozen magnetization contribution has been revealed in the case of the powders. All the mentioned phenomena are strongly dependent on the size and the shape of particles of the powders prepared either in an agate mortar or in a ball mill. Temperature treatment of the powders and the compressed pellets at temperature 1173 K under argon led to a recovery of the applicable properties that are characteristic for the bulk alloys. Results of the earlier quantum mechanical calculations of effects of different arrangement of Mn and Sn atoms in crystal structure of the alloys have been used to discuss the observed properties of the powders and to assess a formation of clusters in magneto-crystalline structure of the alloys. [Display omitted] • The suppression of magnetization and exchange-bias effects has been observed in powders of the Ni 2 MnSn-based alloys. • A non-standard exchange-bias effect has been revealed in the case of the powders. • Results of our earlier quantum mechanical calculations have been used to discuss the observed properties of the powders. • The properties of the powders are identical with properties of the bulk alloys after a treatment of the powders at 1173 K. [ABSTRACT FROM AUTHOR]

Complex study of magnetic, magnetocaloric and structural properties of the Ni 2 MnSn and Ni 1.92 Mn 1.56 Sn 0.52 compounds was performed. The stoichiometric single-crystal of Ni 2 MnSn was prepared by Czochralski method. The remarkable pressure effect on the martensitic magnetization and the martensite-austenite transition temperature T M–A was observed in the Ni 1.92 Mn 1.56 Sn 0.52 compound. The coefficient dT M–A /dp reached value of 18 K/GPa. The already low value of martensite magnetization of Ni 1.92 Mn 1.56 Sn 0.52 was further substantially decreased by external pressure, in contrast with pressure almost insensitive magnetization of the stoichiometric Ni 2 MnSn single-crystal. The pulse magnetic field of 58 T invoked the structural transition at temperature 180 K that is of about 100 K below T M–A of Ni 1.92 Mn 1.56 Sn 0.52 at zero field. An anomalous increase of resistivity of the compound has been observed at temperature range below T M–A , however, it does not copy the sharp change of magnetization at T M–A . The obtained results indicate the important role of interatomic distances on the magnetic ordering and electronic structure of the studied Heusler alloys and are in agreement with the Jahn-Teller mechanism of the martensitic transition in these compounds. [ABSTRACT FROM AUTHOR]

Magnetic and magnetocaloric properties of TbFeAl and GdFeAl were studied in a wide temperature region in magnetic field up to 10 T. They order magnetically below Tc = 196 K and 259 K for TbFeAl and GdFeAl, respectively. The temperature change of ΔT = 1.4 K and 1.6 K was observed in GdFeAl and TbFeAl respectively for a field change of 4 T. Interestingly wide temperature region of significant magnetocaloric effect was observed in both compounds which give rise to relative cooling power of 350 J kg-1 for TbFeAl and 348 J kg-1 for GdFeAl for 4 T field span. [ABSTRACT FROM AUTHOR]

Abstract: The helimagnetic ground state was induced in the hexagonal Y2Fe17 and Lu2Fe17 intermetallics by hydrostatic pressure above 1.05 and 0.3GPa, respectively. The observed incommensurate helical structure was characterized by a propagation vector (00 τz ) and by a metamagnetic transition at the critical field H c. The new incommensurate magnetic structure has been revealed now in Lu2Fe17 at magnetic fields above H c at low temperatures. A detailed pressure-temperature-field evolution of the magnetic structures in Y2Fe17 and Lu2Fe17 is presented. [Copyright &y& Elsevier]