Eric S. Linville

Paramagnetic to antiferromagnetic phase transformation in sputter deposited Pt-Mn thin films

Sputter-deposited, equiatomic Ni-Mn thin films were observed to possess a metastable, nanocrystalline, chemically disordered, fcc (A1) structure. Grain growth and a phase change to a chemically ordered, antiferromagnetic L10 structure were identified by x-ray diffraction (XRD) and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) experiments revealed exothermic signals that correspond to the grain growth and phase transformation reactions. The enthalpy of transformation for the A1 to L10 phase change was calculated as −3.5 kJ/mol, which agress with thermodynamic modeling. An activation energy of 139 kJ/mol was calculated for the phase transformation by the Kissinger method.

Spin tunneling heads above 20 Gb/in/sup 2/

Spin tunneling recording heads above 20 Gb/in/sup 2/ have been fabricated using a bottom tunneling junction stack. The spin tunneling stack is made of Ta/PtMn/CoFe/Ru/CoFe/AlO/NiFe/Ta and stabilized by a permanent magnet abutted junction. The effective junction width is about 0.4 /spl mu/m wide and lapped to the junction with an optimum stripe height. The barrier has resistance area product of 15-20 /spl Omega//spl mu/m/sup 2/, leading to a typical head resistance of around 50 /spl Omega/. Isolated pulses during the spin-stand test shows large signal up to 10 mV. On track error rate floor is better than 10/sup -9/ and the head signal-to-noise ratio is also better than that of. a conventional spin valve GMR head. The areal density estimated (using BER of 10/sup -5/) is above 20 Gb/in/sup 2/.

Exchange anisotropy and micromagnetic properties of PtMn/NiFe bilayers

Magnetic microstructure, exchange induced uniaxial and unidirectional anisotropy and structural transformation have been studied in PtMn/NiFe bilayer films and small elements as a function of annealing time. The relationship between the fcc-fct ordering phase transformation in PtMn and the development of exchange induced magnetic properties in PtMn/NiFe bilayers is complicated by the fact that the transformation occurs throughout the entire volume of the PtMn film, while the exchange between the layers is predominantly an interface effect. Consequently, the development of the exchange anisotropy should depend primarily on the character of the structural transformation at the interface between PtMn and NiFe. The purpose of this article is to correlate the volume phase transformation in PtMn to the development of exchange anisotropy and micromagnetic behavior in PtMn/NiFe bilayers. The interface structure can be inferred from the anisotropy and micromagnetic measurements, leading to a model that explains th...

Magnetic force microscope study of antiferromagnet–ferromagnet exchange coupled films

Magnetic microstructure in micron and submicron size elements made of bilayer antiferromagnet–ferromagnet (AFM/FM) (AFM: NiMn, PtMn, and IrMn; FM: NiFe and CoFe) exchange coupled polycrystalline films have been studied using a magnetic force microscope. AFM/FM elements with various thickness of FM layer (50–500 A) have been examined and compared with nonexchange biased FM elements of the same size, shape, and thickness. Micromagnetic structures observed in AFM/FM elements with thick (>200 A) FM layer indicated that, in addition to unidirectional anisotropy, the AFM layer induces uniaxial anisotropy in a FM layer. Bilayers with a NiMn or PtMn AFM layer exhibited higher induced uniaxial anisotropy than ones with IrMn. In the elements with a thin (<100 A) FM layer and NiMn or PtMn as an AFM layer, a local switching of the magnetization direction under an external applied field has been observed. The size of the “switched” areas depends on the material and thickness of the FM and AFM layers. No local switchin...