PtMn-based Spin Valves Research Articles

Irradiation-controlled giant magnetoresistance of PtMn-based spin valve

He + -ion irradiation resulted in the direct ordering of PtMn without postannealing. Samples were irradiated with 2MeV He+ ions and a beam current of 1.08μA∕cm2 such that the corresponding surface temperature was 190°C. The exchange bias direction was set in situ during irradiation in a field of 900Oe. A high giant magnetoresistance (GMR) ratio of 11% was obtained in PtMn-based spin valves after He+ irradiation. The GMR is completely eliminated after it is irradiated with oxygen ions at 42keV. Combining He+ with oxygen-ion irradiation can provide magnetic patterning for GMR sensors.

Effect of Ni100−xCrx seedlayer on transport and magnetic properties in PtMn-based spin valves

The effect of cosputtered Ni100−xCrx seedlayer on transport and magnetic properties in PtMn-based synthetic spin valves has been studied. We found that magnetoresistance (MR) ratio increases with increasing Cr content, and reached over 15% when the Cr content is in the range of 38–41at.%. The MR ratio drastically decreases to less than 2% when the Cr content is higher than 41at.%. We found that the dependence of transport and magnetic properties on the Cr content of the NiCr seed layer is strongly correlated with the crystallographic orientation of the PtMn and CoFe∕Ru∕CoFe∕Cu∕CoFe∕NiFe∕Cu layers grown on the seedlayer.

Effects of ion-beam irradiation on the L10 phase transformation and their magnetic properties of FePt and PtMn films (Invited)

ABSTRACTIon-beam irradiation shows enhancement or degradation of magnetic properties on L10 phase of FePt and PtMn films. A highly ordered L10 FePt phase was directly achieved by using 2 MeV He-ion irradiation without conventional postannealing. The in-plane coercivity greater than 5700 Oe can be obtained after disordered FePt films were irradiated at the beam current of several μA/cm2 with the ion does of 2.4×1016 ions/cm2. The high beam-current-density results in direct beam heating on samples. In addition, the irradiation-induced heating process provides efficient microscopic energy transfer and creates excess point defects, which significantly enhances the diffusion and promotes the formation of the ordered phase. Consequently, the direct ordering of FePt took place by using ion-irradiation heating at temperature as low as 230°C. The comparison has been made on the [Fe/Pt]10/C films by RTA and high current-density He irradiation. Although RTA and ion irradiation both reach high coercivity, ion irradiation seems to suppress the (001) texture, leading to isotropic Hc. Ion-beam irradiation can also be applied to the transformation of PtMn. An ordered PtMn phase, a large exchange field and a high GMR ratio (11%) were obtained in PtMn-based spin valves by using 1.25 μA/cm2 He-ions. On the other hand, Ge-ion and O-ion irradiation completely destroyed the ferromagnetism of FePt and GMR of PtMn-based spin valves, respectively. We propose a novel approach to achieve magnetic patterning by using ion irradiation, which can be applied for patterned media and magnetic sensors.

Influence of carbon ion dose on exchange field and GMR of irradiated PtMn-based spin valves

The effects were investigated of carbon ion dose on the exchange field and GMR ratio of irradiated PtMn-based spin valves. The exchange field increases with increasing dose in the low ion-dose-regime, which is attributed to the increase in PtMn(C) formation. The maximum enhancement of the exchange field can be as large as 50% for the ion dose of 2.0/spl times/10/sup 14/ ions/cm/sup 2/. The reduction of the exchange field in the high-dose regime is probably due to the intermixing or carbon residue at the interface. The giant magnetoresistance (GMR) ratio monotonically decreases with increasing carbon dose. Ion irradiation shows different effects on fcc and fct PtMn samples. By proper annealing prior to irradiation, we can obtain a large enhanced exchange field and a reasonably good MR ratio.

Antiferromagnetically coupled hard/Ru/soft layers and their applications in spin valves

Antiferromagnetically coupled hard/Ru/soft triple layers have been fabricated using ultrahigh vacuum sputtering. A series of experiments has been carried out to study the dependence of the exchange-coupling field on the thickness of the soft layer which is either CoFe or NiFe, while the hard layer is CoCrPt. It was found that this type of synthetic structure exhibits a significantly higher exchange coupling field as compared to the conventional antiferromagnet/ferromagnet exchange coupled structures. The use of these synthetic structures as the pinned and pinning layers has resulted in spin valves with a magnetoresistance ratio in the range of 5%–7% and a thermal stability that is better than those of IrMn-based and comparable to those of PtMn-based spin valves.

Enhancement of exchange field and reduction of GMR in PtMn-based spin valves by ion irradiation

C-ion irradiation was performed on PtMn-based spin valves and the effects of ion irradiation on magnetoresistance (MR) and on the exchange field were investigated. When ion irradiation was performed prior to post-annealing, the exchange field was substantially enhanced after annealing, especially for an annealing temperature below 240 °C. The enhancement could be related to the formation of PtMn(C) phase, which might accelerate the formation of ordered PtMn phase and might increase the anisotropy of PtMn. Although the majority of C ions located in capping layers Ta and PtMn, small amounts of C ions may go into the interface of CoFe/Cu/CoFe, leading to a small MR.

Nano-oxide layers and PtMn-based specular spin valves and heads

Nano-oxide layers and relevant spin valves have been investigated. Morphology observation shows that the nano-oxide layers are adequate for current spin valves as thin, dense, and uniform specular reflection layers to enhance scattering of electrons at interfaces. Large enhancement of /spl Delta/R/R (/spl sim/16% with a /spl Delta/R/spl sim/3.7 /spl Omega//sq) has been achieved with the help of specular reflection. Both full film and read heads data demonstrated thermally stable magnetic performance. Addition of nano-oxide layers does not compromise head ESD robustness. Readers with nano-oxide layers show amplitude sensitivity of up to 10 mV//spl mu/m and are suitable for >50 Gb/in/sup 2/ recording applications.

Track width definition of giant magnetoresistive sensors by ion irradiation

We describe the concept of using irradiation with light energetic ions in conjunction with a mask to define the edges of giant magnetoresistive sensors without milling. The irradiated material undergoes substantial interfacial mixing, and consequent loss of magnetoresistance (MR), accompanied by small changes in resistivity, and no significant change in magnetic moment. The ion species and energy may be chosen to minimize lateral scattering as they pass through the sensor film. Modeling of a perfect mask edge above a sensor film of thickness /spl sim/240 /spl Aring/ irradiated with a well-collimated ion beam indicates that sensor edge definition of /spl plusmn/20 /spl Aring/ is achievable-a vast improvement over sensor edges generated using ion milling, which may run to hundreds of Angstroms in width. Experimental data from irradiation of typical NiO, IrMn, NiMn and PtMn-based spin valves using 700 keV N/sup +/ ions indicate that doses between 10/sup 15/ and 10/sup 17/ ions/cm/sup 2/ are sufficient to diminish the MR of the films to below 5% of the as-grown value. Changes in MR caused by the irradiation are stable against annealing at temperatures typical for setting these sensors.

Reliability of PtMn-based spin valves

This paper addresses the lifetime characteristics of standard and synthetic spin valves of different PtMn antiferromagnet (AFM) thicknesses and compositions. It shows that loss of magnetoresistance with time at elevated temperature is less pronounced for synthetic structures, for thinner PtMn AFM films exchange-annealed for relatively longer times, and Pt-rich compositions of PtMn. The lifetime temperature T/sub max/ is defined as the maximum operating temperature for the spin valve that results in less than a 10% drop in output for a five-year 50% duty cycle. The generalized prediction of lifetime temperature T/sub max/ from the more usable unblocked ratio (UBR) point on the UBR-versus-temperature curve is complicated by test conditions and initial Hex values. For Hex values and reverse field magnitudes for the sheet film spin valve samples tested here, the tolerable UBR was in the 6-8% range, and T/sub max/ values in the 170/spl deg/-205/spl deg/C range. Choosing the correct reverse field for /spl Delta/T/sub b/ measurements was important for synthetic structures because of the interaction between the applied field and the coupling field between the inner and outer pinned layers in the synthetic structure. Finished heads show T/sub max/ values that are lower by 40/spl deg/-55/spl deg/ for the five-year 50% duty cycle criterion compared to sheet films. This highlights the importance of processing environments, especially in slider fabrication, and imposes a further restriction on the acceptable sheet film tolerable UBR, reducing it to 3-4%. Activation energies from lifetime tests are in the range 2.2 to 2.6 eV for all samples including finished sliders, which indicates that differences in lifetimes are not associated with large variability in the activation energy of depinning within the PtMn system. The time-dependence of magnetic properties such as interlayer coupling (H/sub ilc/) and coercivity (H/sub c/) of the free layer is very important and exhibits runaway behavior with time. It must be monitored for deleterious effects.

Microstructural evolution in PtMn-based spin-valves induced by heat treatment

Annealing time effect on the magnetotransport properties was investigated for Si/alumina/Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta samples having different PtMn thickness (10–30 nm). Post-deposition heat treatment was performed using a vacuum furnace with 3 kOe field at 270°C up to 35 h. The thermally activated atoms diffused to other layers through grain boundaries during the heat treatment with longer annealing hours resulting in deteriorating Δ R/ R. This effect is more profound in films with thicker PtMn layers where interface became rougher after annealing.

Enhancement of MR ratios using thin oxide layers in PtMn and α-Fe 2O 3-based spin valves

Spin valves having thin oxide layers in the pinned and/or free layers were prepared by sputtering. MR ratios of the spin valves were increased from 8.1 to 11.9% by inserting the oxide layer into the pinned layer in Ta/PtMn/CoFe/Cu/CoFe/Ta spin valves. MR ratio of 13.9% and considerably large sheet Δ R of 2.55 Ω were obtained in the PtMn-based spin valves having the oxide layer in the pinned and free layer. Larger MR ratio of 17.3% and the sheet Δ R of 1.3 Ω were obtained in the PtMn-based dual-type spin valves having the oxide layer in both pinned layers. α-Fe 2O 3 based spin valves having thin oxide layers were also prepared. MR ratios of the spin valves were increased from 11.9 to 14.3% by inserting the oxide layer into the free layer in α-Fe 2O 3/CoFe/Cu/CoFe/Ta spin valves. The enhancement of the MR ratios may be attributed to the specular scattering effect of the conduction electrons by the thin oxide layers.

Enhanced GMR in PtMn-based spin valves with specular reflective thin oxide layers

PtMn based Spin-valves with or without specular reflective thin oxide layers, OL, were prepared by sputtering. The MR ratios and /spl Delta/Rs of the spin-valves without OL were about 8% and 1.2 /spl Omega/. The values were increased up to 12-15% and /spl supe/2.6 /spl Omega/ by inserting an OL into the pinned and free layers. PtMn based spin-valves with synthetic AF and OL as the pinning layers were also studied. The MR ratio and /spl Delta/Rs were about 11% and 2.9 /spl Omega/. These PtMn based spin-valves showed better thermal stability than IrMn based spin-valves.

RuRhMn and PtMn specular spin-valve with magnetic oxide layer

In this paper, RuRhMn-based and PtMn-based spin valves with magnetic oxide layer (MOL) inserted in the free layer, pinned layer, or both layers were studied. Both magnetoresistance (MR) ratio and /spl Delta/R/sub sq/ were increased in these spin valves, due to the insertion of MOL. Theoretical calculation based on semi-classical Boltzmann equation for transport indicated that the enhancement of MR ratio can be attributed to the strong specular scattering at interface with MOL. PtMn specular spin valves are more thermally stable than RuRhMn spin valves. Their thermal stability can be further improved by using a synthetic pinned layer with MOL, where the effective exchange field degrades less than 20% when the temperature is increased up to 350/spl deg/C.

Exchange coupling and stability of PtMn-based spin valves

The exchange coupling and stability of spin valves with antiferromagnetic (AF) PtMn films were investigated through the correlation between the magnetic properties and their microstructures. The exchange coupling field (H/sub ex/) decreases during iterative MR measurements and this decrease associates closely with the changes in the rotational hysteresis loss (W/sub r/), exchange anisotropy energy (K/sub e/) and blocking temperature (T/sub b/) distribution. The ordering of PtMn films, featuring an antiphase configuration, is found to play a significant role in determining the exchange coupling properties and stability of these spin valves.