We have studied the magnetic properties of an off-stoichiometric Heusler shape memory alloy Ni51.9Mn23.2Ga24.9 with near room temperature martensitic transition at 306 K. The temperature dependence of magnetization revealed a thermal hysteresis and a ∼10% decrease in spontaneous magnetization across the martensitic transition. In-situ X-ray diffraction measurements at different temperatures revealed a negative shape strain of 4.8%. Heat absorptions measurements indicated that the martensitic structural transition may take place in multiple steps.

Magnetic properties of Ni81Fe19/Al2O3/Ni81Fe19 tunneling junctions are studied for different Al thicknesses and plasma oxidation times. A maximal magnetoresistance of 34% is obtained with Al thickness of 20 Å. Magnetometry reveals large exchange bias fields (∼400 Oe) over a wide range of barrier thicknesses, indicating junctions of high quality. Transport measurements conducted on junctions before and after thermal annealing show a dramatic improvement in barrier quality after annealing. Interlayer coupling fields have been measured as a function of barrier thickness for different oxidation times.

We report on structural, magnetic, transport, and spin-polarization measurements of the Heusler alloys Co2MnSi and NiMnSb. Laue diffraction patterns confirm the single-crystal nature of Co2MnSi. Room-temperature transport measurements show a negative magnetoresistance in NiMnSb. Point-contact Andreev reflection measurements of the spin polarization yield polarization values for Co2MnSi and NiMnSb of 56% and 45%, respectively. Temperature dependence of resistivity for Co2MnSi reveals a relatively large residual resistivity ratio (rho(293 K)/rho(5 K)) typical of single-crystal Heusler alloys. In NiMnSb, resistivity and magnetization as a function of temperature show evidence of a magnetic phase transition near 90 K.

The exchange bias and crystalline texture of the multilayer structure (Ta/Al/seed/Fe50Mn50/Ni81Fe19/Al2O3/Ni81Fe19/Al/Ta with seed=Ni81Fe19 or Ni81Fe19/Cu) has been characterized. Measurements indicate an abrupt decrease in exchange bias of the Ni81Fe19 pinned layer for samples with very thin seed layers, and exchange bias as high as 325 Oe for thicker seed layers. Fluctuation of exchange bias with thickness was greatly reduced for the Ni81Fe19/Cu seed configuration. X-ray diffraction measurements demonstrate a correlation between exchange bias and strong (1 1 1) texture of FeMn. The results suggest a high sensitivity of Ni81Fe19 roughness and texture on deposition conditions, and corroborate previous observations of roughness in ultrathin NiFe films.

We observe a strong correlation between magnetization relaxation and electrical resistivity in thin Permalloy (Ni$_{81}$Fe$_{19}$, ``Py'') films. Electron scattering rates in the films were affected by varying film thickness and deposition conditions. This shows that the magnetization relaxation mechanism is analogous to ``bulk'' relaxation, where phonon scattering in bulk is replaced by surface and defect scattering in thin films. Another interesting finding is the increased magnetization damping with Pt layers adjacent to the Py films. This is attributed to the strong spin-orbit coupling in Pt, resulting in spin-flip scattering of electrons that enter from the Py.