Ryoichi Nakatani

Exchange coupling between antiferromagnetic Mn-Ir and ferromagnetic Ni-Fe layers

Exchange couplings between antiferromagnetic Mn–Ir and ferromagnetic Ni–Fe layers have been investigated while varying the Mn–Ir composition. These exchange couplings appeared at room temperature at Ir compositions between 20 and 46 at.%. The maximum exchange coupling field of 3.2 kA/m was obtained for Mn–20 at.%Ir(59 nm)/Ni–Fe(20 nm)/Zr(10 nm). Dependence of the exchange coupling fields on each layer thickness was also investigated. The Mn–Ir/Ni–Fe bilayers maintained high exchange coupling fields at Mn–Ir layer thicknesses above 10 nm.

Magnetic properties of multilayered Fe-C film formed by dual ion beam sputtering

The magnetic properties of both single-layered and multilayered Fe-C films formed by dual ion beam sputtering are studied. When the C concentration in Fe-C films increases, the relative permeability of the film increases and the coercivity decreases. The relative permeability of single-layered Fe-9at%C film with a magnetostriction constant nearly zero, is 550 at 5 MHz, even though that of pure Fe is only 150. When a multilayered film is made by alternating 5nm thick permalloy intermediate layers with 95nm thick Fe-C films, the soft magnetic properties of the resulting film show tremendous improvement. Multilayered Fe-9at%C film shows a relative permeability of 1400 and a coercivity of 200A/m. Compressive stress up to -2 × 109N/m2exists in this film. This stress can be relieved by heat treating the film in Ar, which improves the soft magnetic properties. The Fe-9at%C/permalloy multi-layered film annealed for 1 hour at 400°C shows a saturation magnetic flux density of 2.1T, a relative permeability of 3000 and a coercivity of 80 A/m.

Giant magnetoresistance in Ni-Fe/Cu multilayers formed by ion beam sputtering

I n t r o d u u various magnetic multilayered films.1 In Fe/Cr, CO/& and Cornu multilayers, the oscillatory magnetoresistance changes were observed as the thickness of the non-magnetic layer was varied.l-4 However, Ni-Fe based multilayers to show oscillatory magnetoresistance changes have not yet been reported. This study investigates Ni-Fe/Cu multilayers formed by ion beam sputtering. Ion beam sputtering has not been used much in the formation of the multilayers to show high magnetoresistive effects. We observed magnetoresistance oscillation as the thickness of the Cu layer changes in NiFe/Cu multilayers. The Ni-Fe(1 nm) / Cu(1 nm) multilayer shows magnetoresistance of 18.8% at room temperature. Experimmd I The Ni-Fe/Cu multilayers were prepared using an ion beam sputtering I apparatus. The Ni-20at%Fe, Cu and Fe plates were used as targets. The I acceleration voltage of the ion gun was 300 V and the ion current was 30 mA.

Magnetic properties and film structures of Fe/C multilayers

The magnetic properties and film structures of Fe/C multilayers (period: 5–50 nm) formed by ion beam sputtering are studied. The coercivity in the easy axis direction is decreased from 380 A/m (=4.8 Oe) to 25 A/m (=0.3 Oe) by reducing the period from 50 to 5 n. The relative permeability increases to a maximum of approximately 3000 with increasing C layer thickness. Cross‐sectional transmission electron microscopy and Auger electron spectroscopy show that Fe layers are clearly separated by C layers, resulting in small Fe crystallites.

Oscillation of magnetoresistance in [Ni–Fe/Cu]20/Cu/Fe multilayers with thickness of Cu spacer neighboring Fe buffer layer

In [Ni–Fe (1.0 nm)/Cu(1.0 nm)]20/Cu(t nm)/Fe(5.0 nm) multilayers with giant magnetoresistance effects, oscillations of magnetoresistance ratio and preferred orientation depending on Cu spacer thickness t have been observed. Corresponding to the oscillation of the magnetoresistance ratio, the preferred orientation oscillates between <100≳ and <111≳, though the thicknesses of each Ni–Fe and Cu layer in the multilayer are fixed. Both the periods of the oscillations are about 0.6 nm. When the multilayers have stronger <100≳ and weaker <111≳ preferred orientations, they show higher magnetoresistance ratios.

Relationship between film structure and exchange coupling in MnIr/NiFe films

Abstract Exchange couplings between Mnue5f8Ir antiferromagnetic layers and Niue5f8Fe magnetic layers have been investigated in Hf (8 nm)/Mnue5f8Ir (16 nm)/Niue5f8Fe (5 nm)/Hf (7 nm)/Si(10 0) films formed by ion-beam sputtering. When the acceleration voltage of the ion gun was higher than 600 V and the ion current was 50–100 mA, the FCC-(1 1 1) texture of the Mnue5f8Ir layer became strong and the Mnue5f8Ir crystallites were relatively large. The large crystallites caused strong exchange couplings between the Mnue5f8Ir layers and the Niue5f8Fe layers. The highest exchange bias field was 14.8 kA/m. A Ta (7 nm)/Mnue5f8Ir (14 nm)/Niue5f8Fe (5 nm)/Ta (6 nm)/Si(1 0 0) film was also prepared by RF sputtering. The RF-sputtered film had the larger crystallites than the ion-beam-sputtered films. The exchange bias field was 23.1 kA/m.

Changes in soft magnetic properties of Fe multilayered films due to lattice mismatches between Fe and intermediate layers

Fe multilayered films with various intermediate layers are formed. Their magnetic properties and film structures are examined to understand the mechanism originating soft magnetic properties. The soft magnetic properties change with the lattice mismatches between Fe and intermediate layers, showing low coercive force and high relative permeability at lattice mismatches from 0.4 to 1.2%. It is thought that the lattice mismatches above 0.4% decrease Fe crystallite size and improve soft magnetic properties. Although Fe crystallite size is small at the lattice mismatches above 1.2%, the soft magnetic properties are poor. This is because the large lattice mismatch increases internal stress and magnetic anisotropy energy. This report indicates that the good soft magnetic properties are obtained when both Fe crystallite size and internal stress are small.

Magnetic properties and corrosion resistance of Fe-based sputtered films

The effects of elements added to Fe-based sputtered films are investigated to obtain magnetic thin films with a high-saturation magnetic flux density, Bs, a zero magnetostriction constant, λs, and high corrosion resistance. The Fe films, sputtered at argon pressures below 10 mTorr, have the same Bs as bulk samples. They also show high corrosion resistance. Although the λs of Fe film has a large absolute value, zero-magnetostriction films are obtained by the addition of 1 to 5at% Si, Cr, Mo, Ni, Ru or Rh. Samples containing Ni or Rh maintain a high Bs, of about 21 kG. However, the addition of Si, Mo and Cr cause a marked deterioration in corrosion resistance, while samples containing Ni, Ru or Rh show high corrosion resistance. The anodic polarization curves show that films with high corrosion resistance have high pitting potentials. This result suggests that the pitting is dominant in the corrosion of Fe-based films.

Magnetoresistive response of giant-magnetoresistive NiFe/Cu multilayer elements

Abstract The basic characteristics of giant magnetoresistive NiFe/Cu multilayer elements have been investigated for potential application to magnetic recording heads. The multilayers are formed on glass substrates by ion beam sputtering, and consist of eight bilayers of [Ni-19%Fe(1.6 nm)/Cu(2.2 nm)] on top of a 5 nm Fe buffer layer. This structure has an average magnetoresistivity of 5.7% in the sheet condition. The multilayer is divided into areas 5–20 μ m wide and 4–400 μ m long, on which Cr/Cu/Cr electrodes are grown with a separation of 2–150 μ m. The response curves in a 50 Hz ac magnetic field show hysteresis. The output voltage does not depend on the element size or aspect ratio, or on the angle between the longitudinal direction of element and the applied magnetic field. The half-width of the response curve does not depend upon the element size either, although it depends slightly on the angle between the longitudinal direction of element and the applied magnetic field. The influence of a bias field on the response curve has also been observed.

Exchange Coupling Of (Mn-Ir.Fe-Mn)/Ni-Fe-Co And Ni-Fe-Co/(Mn-Ir. Fe-Mn) Films Formed By Ion Beam Sputtering

We investigated exchange couplings between magnetic layers and antiferromagnetic layers in (Mn-Ir, Fe-Mn)/Ni-Fe-Co and Ni-Fe-Co/(Mn-Ir, Fe-Mn) films formed by ion beam sputtering. We changed a stacking order between the magnetic layers and antiferromagnetic layers, and the thickness of the antiferromagnetic layers. In both the Fe-Mn/Ni-Fe-Co and the Ni-Fe-Co/Fe-Mn films, high exchange bias fields applied to the Ni-Fe-Co layers were observed, when the thickness of the Fe-Mn layer was 10-20 nm. When the Mn-Ir layers were formed on the Ni-Fe layers, the high exchange bias fields were also observed. However, the exchange bias fields were very low when the Mn-Ir layers were formed under the Ni-Fe layers. The decrease of the exchange bias field was caused by the deterioration of the (111) texture near the top surface which faces the Ni-Fe layer in the Mn-Ir layer.