Search

Laminated [([Fe.sub.0.7][Co.sub.0.3]).sub.88][Zr.sub.7][B.sub.4][Cu.sub.1] amorphous HITPERM/Si[O.sub.2] multilayer thin films have been studied by room-temperature (RT) pulsed inductive microwave magnetometry (PIMM) in single, bilayer, and trilayer films. Switching has been measured in a multilayer film with six (50 nm) HITPERM layers, separated by five (2 nm) Si[O.sub.2] layers. Films were investigated by conventional transmission electron microscopy (TEM), high-resolution TEM (HREM), and superconducting quantum interference device (SQUID) magnetometry. HREM and TEM show BCC FeCo nanocrystals to nucleate on top of Si[O.sub.2] layers. Plan view TEM on the top layer reveals FCC nanocrystals that align in chains with spacing of ~50-100 nm. SQUID magnetometry shows reversal to begin by rotation in a single layer for H < 14.4 kA/m (180 Oe) followed by nearly simultaneous reversal of several layers. A final switching event is thermally activated, requiring fields in excess of 8 kA/m (100 Oe) to switch at 2 K, but switching at the same field as other layers for elevated temperatures (RT). Index Terms--Multilayers, PIMM, soft magnet, thermally activated switching.

We detail crystal growth and characterization of Ni-Mn--Ga ferromagnetic shape-memory alloys (FSMA). Structural characterization includes x-ray Laue diffraction and x-ray diffraction (XRD) using [Theta]-2[Theta] scans. Differential scanning calorimetry (DSC) and DC magnetization measurements have been used to probe structural and magnetic phase transformations in these materials. For the first time, the temperature dependence of magnetic torque reveals a variation of the magnetic anisotropy in stoichiometric [Ni.sub.2] MnGa crystals. We also report on the effect of post-annealing on the martensitic phase transition (MPT) temperature. A [Ni.sub.52.7][Mn.sub.22.6][Ga.sub.24.7] crystal exhibits an onset of the transformation at 304 K. The temperature hysteresis during a heating-cooling process and the full width of the transition are observed to be 2 and 10 K, respectively, for this crystal.

Cast alloys and melt-spun ribbons with nominal compositions of Sm(CobalFe0.31Zr0.05CU0.04Bx)z (x = 0.02-0.04, z = 7.5-12) have been synthesized and characterized in a temperature range of 10-1273 K and at fields up to 51. The main phase in the as-cast alloys exhibited a Th2 Ni17 type structure, with a strong uniaxial anisotropy. Minor phases with a TbCu7 and/or CaCu5 structure emerged as z (3d/R) decreased. As a result, the anisotropy field (HA) increased from 67 to 120 kOe, while 4πM8 fell from 12.8 to 10.5 kG at 300 K when z was decreased from 12 to 7.5. For melt-spun ribbons, they are nano-structured in nature and magnetically hard, even in the as-spun state. By lowering the value of z(3d/R) and raising the B content, a finer microstructure and a higher Hci were obtained. Hard magnetic properties of Hci = 4.9-12 kOe, 4πM8 = 9.0-12.0 kG at 300 K have been obtained from ribbon samples. Among them, Sm(CobalFe0.31Zr0.05Cu0.04B0.02)10 ribbon showed the highest (BH)max of 10.8 MGOe at 300 K. A Henkel plot analysis suggested the existence of exchange-coupling interaction between the magnetically hard and soft phases in the ribbon materials. [ABSTRACT FROM AUTHOR]

Laminated (Fe0.7 Co0.3)88 Zrγ B4 Cu1 amorphous HITPERM/SiO2 multilayer thin films have been studied by room-temperature (RT) pulsed inductive microwave magnetometry (PIMM) in single, bilayer, and trilayer films. Switching has been measured in a multilayer film with six (50 nm) HITPERM layers, separated by five (2 um) SiO2 layers. Films were investigated by conventional transmission electron microscopy (TEM), high-resolution TEM (HREM), and superconducting quantum hi reference device (SQUID) magnetometry. HREM and TEM show BCC FeCo nanocrystals to nucleate on top of SiO2 layers. Plan view TEM on the top layer reveals FCC nanocrystals that align in chains with spacing of ∼ 50-100 nm. SQUID magnetometry shows reversal to begin by rotation in a single layer for H < 14.4 kA/m (180 Oe) followed by nearly simultaneous reversal of several layers. A final switching event is thermally activated, requiring fields in excess of 8 kA/m (100 Oe) to switch at 2 K, but switching at the same field as other layers for elevated temperatures (RT). [ABSTRACT FROM AUTHOR]