Kazuko Inoue

Magnetic-Field-Induced Martensitic Transformation in Ni2MnGa-Based Alloys.

The magnetic controllability of the thermoelastic martensitic transformation, which is the origin of the shape-memory effect, has been investigated. We have carried out neutron diffraction measurem...

Magnetic Properties of C14-Laves Phase RMn2

The temperature dependence of magnetic susceptibility and magnetization of metastable C14-RMn 2 (R=Y, Gd, Tb, Dy and Yb), synthesized at high pressures, has been measured. YMn 2 is an itinerant paramagnet over the whole range of temperatures. GdMn 2 , TbMn 2 and DyMn 2 are ferromagnetic at low temperatures, while their susceptibilities beyond T C obey the Curie-Weiss law. YbMn 2 is a paramagnet down to 4.2 K whose susceptibility suggests antiferromagnetic interactions. These magnetic properties are discussed together with those of other stable C14-RMn 2 . Similary to stable C14- and C15-RMn 2 , the appearance of local magnetic moments of itinerant 3d Mn electrons of C14-RMn 2 at low temperatures are determined by the Mn–Mn distance. The Mn atom has a magnetic moment for light rare earths, whereas no moment for heavy rare earths. The critical substance for the onset of Mn moments is TbMn 2 .

Neutron diffraction study of Sr2Mn2O5

Abstract The crystal and magnetic structure of SrMnO 2.5 has been investigated by neutron power diffraction from 20 to 425 K. The compound has orthorhombic crystal structure with the unit cell dimensions a =0.55307(4), b =1.07829(8), c =0.38145(3) nm at 425 K, where space group is Pbam and Z =4. Below T N =375 K, an antiferromagnetic order occurs and the magnetic unit cell is orthorhombic with the dimensions a m = a c , b m = b c , c m =2 c c , where a c , b c and c c are the parameters of the crystallographic unit cell. The ferromagnetic and antiferromagnetic coupling coexist in the c-plane according to the difference of Mn–O–Mn angle and the coupling between adjacent planes is antiferromagnetic. The direction of the magnetic moments is along the crystallographic b-axis. The magnitude of magnetic moment at 20 K is 3.44 μ B /Mn.

Phase behavior in the system LaxSr1−xMnO(5+x)/2 (x=0.8–1.0) with trivalent state of manganese ion

Abstract The oxygen defect perovskite La x Sr 1− x MnO (5+ x )/2 phases ( x =0.8–1.0) with valence state adjusted to trivalent manganese ion have been prepared by reducing oxygen content from the series of La x Sr 1− x MnO 3 solid solutions. These phases have been characterized by powder X-ray diffractometry and magnetization measurement. The crystal systems of La x Sr 1− x MnO (5+ x )/2 are orthorhombic ( x =1.0–0.9) and rhombohedral ( x =0.8). The phase of La x Sr 1− x MnO 3+ δ for x =0.9 shows structural change from rhombohedral to orthorhombic symmetry by degree of oxygen nonstoichiometry, while the compounds for x =1.0 and 0.8 do not show structural change by oxygen nonstoichiometry. The random distribution of the oxygen vacancies are assumed in each structure. For x =0.8, the behavior of the temperature dependence of gram magnetization is quite different for finite-field cooling and for zero-field cooling, whereas the magnetic transition temperature exists at around 138 K for both cases. It seems that the magnetic ordered state of this sample is weak ferromagnetic.

Paramagnetic Properties of C15-Laves Phase RMn2 (R = Gd, Tb, Dy and Ho).

The temperature dependence of magnetization and magnetic susceptibility of stable C15-Laves phase RMn 2 ( R=Tb, Dy and Ho) has been measured from 77 K to about 750 K. It obeys the Curie-Weiss law. However, there is a change of the slope of inverse susceptibility near 400∼500 K. The effective magnetic moments, especially those above the change of the slope, are nearly equal to \(g\sqrt {J(J+1)}\) of R 3+ . The paramagnetic Curie temperatures at low temperatures are positive and change systematically with the lattice spacing, ascribed to the ferromagnetic R–R interaction like those of C14-RMn 2 . On the other hand, the paramagnetic Curie temperatures at high temperatures are negative. The temperature dependence of the susceptibility of C15-GdMn 2 has also been measured and is discussed.

Thermal expansion of C14-laves phase RMn2 (R=Y, Gd, Dy and Yb)

The temperature dependence of lattice spacing of metastable C14-Laves phase RMn 2 (R=Y, Gd, Dy and Yb) has been measured up to 300 K by X-ray diffraction. Large thermal expansion was observed especially for R=Y and Dy. GdMn 2 shows a structural transition from hexagonal to orthorhombic below 80 K accompanied with a volume expansion. This indicates the appearance of a local magnetic moment of Mn 3d electrons with an antiferromagnetic order. The results are discussed together with the data on other stable C14-RMn 2 and metastable C14-TbMn 2 . It is shown that the appearance of local magnetic moment of itinerant Mn 3d electrons of C14-RMn 2 at low temperatures is mainly determined by the Mn-Mn distance. C14-YMn 2 , TbMn 2 and DyMn 2 are the critical substances for the onset of Mn moment.

Magnetism of C14-RMn2 (R Y, Gd, Tb, Dy and Yb)

Abstract Magnetic properties of metastable C14-RMn 2 Laves phase (R  Y, Gd, Tb, Dy and Yb), have been measured. YMn 2 and YbMn 2 are paramagnetic down to 4.2 K. GdMn 2 , TbMn 2 and DyMn 2 are ferromagnetic at low temperatures and the temperature dependence of their susceptibilities obeys the Curie-Weiss law at high temperatures. An antiferromagnetic order of Mn local moments for GdMn 2 and TbMn 2 has been suggested. These properties are discussed together with those of other stable C14-RMn 2 (R  Pr, Nd, Sm, Ho, Er, Tm and Lu). The onset of local moments of itinerant Mn 3d electrons are mainly determined by the MnMn distance.

Electrical Resistivity of Gold-Chromium Alloys with High Concentration of Chromium

The electrical resistivity and the magnetic susceptibility of Au-Cr alloys with high concentration of chromium up to 26 atomic percent have been measured from 4 to 1000°K. The electrical resistivity shows no sharp anomaly but a broad peak above the Neel temperature. In the paramagnetic region, the resistivity decreases with increasing temperature. In order to analyze this anomalous temperature dependence of the resistivity, the magnetic part of the resistivity was estimated by subtracting the resistivity of gold as a phonon contribution from the observed one. It was found that the magnetic resistivity is proportional to - c log T , where c is the chromium concentration and T the temperature. This result seems to be explaind by an extended Kondo effect. On the other hand, a modification of Blatts theory is also discussed to explain the decrease of the resistivity. A similar decrease in the resistivity with temperature in several noble metal alloys with high concentration of 3 d metals and in other alloys ...

55Mn nuclear magnetic resonance study of high-pressure synthesized hexagonal DyMn2, TbMn2 and GdMn2

Abstract The ground state magnetic properties of high-pressure synthesized Laves phase compounds with the hexagonal C14 structure, DyMn 2 , TbMn 2 and GdMn 2 , were investigated by 55 Mn nuclear magnetic resonance technique and compared with those of the equilibrium phases with the cubic C15 structure. We observed two different signals in zero field for DyMn 2 , which are just the same as those for the C15 phase, indicating the coexistence of magnetic and non-magnetic manganese sites. For TbMn 2 , a zero-field spectrum with two peaks was observed in the frequency range below 80 MHz, suggesting that the manganese moment becomes unstable and that manganese atoms are partially non-magnetic, which is in contrast to large and stable magnetic moments in the C15 phase. For GdMn 2 , a broad zero-field spectrum was observed just in the same frequency range as that of the C15 phase, indicating that all manganese atoms have stable large moments.

Kondo Effect in Cu and Ag Alloys with High Concentration of Mn

The electrical resistivities of Gu-Mn and Ag-Mn alloys with Mn concentration from 1 to 25 and 22 atomic percents, respectively, have been measured from 4 to 1000 K. The temperature dependence of the resistivity in both alloys shows no sharp anomaly but a broad maximum above the Neel temperature. Above this maximum temperature, the resistivity decreases with increasing temperature. The magnetic part of the resistivity is estimated by subtracting the resistivity of pure Cu or Ag from the observed one. For all the Mn concentrations studied, the temperature dependence of the magnetic resistivity is well expressed as R mag ( T )=- c (X+Y c )ln ( T 2 + Z 2 c 2 ) 1/2 + R 0 , the where c is the concentration of Mn, T the temperature and X, Y, Z and R 0 constants. This fact suggests that in concentrated alloys the RKKY interaction between Mn impurities plays an important role in the s - d exchange scattering of conduction electrons.