Using different Mn-oxides to influence the magnetic anisotropy of FePt in bilayers with little change of the exchange bias field

We have investigated the exchange coupling between a bottom FePt thin film layer capped withdifferent Mn-oxides. Results have shown that the magnetization reversal of the soft FePt layer isinfluenced strongly by the capped Mn-oxide layer (Mn, MnO, and Mn3O4), as revealed by theenhanced coercivities. Typical temperature dependent magnetization between zero-field cooled(ZFC) and field cooled (FC) scans was observed in the Mn-oxide (8%O2/Ar)/FePt bilayer thatexhibited a blocking temperature (TB 120 K) close to the Ne`el temperature, TN, of MnO.However, the Mn/FePt bilayer exhibited unusual temperature dependent of M vs. T, implying thatintermixing between Mn and FePt interfaces formed an AF FeMn that may have enabled a highirreversibility temperature (Tirr. 400 K) compared to almost identical ZFC and FC curves fromweaker exchange coupling between FePt and the Mn3O4 created with 21 and 30%O2/Ar depositionconditions

Modulating the magneto-crystalline anisotropy and the exchange bias field in CoFe/(Co,Fe)O bilayers using ion-beam bombardment and single crystalline substrates

We report the effects of ion-beam bombardment on the room temperature and low temperature magnetic properties of ferromagnetic CoFe/antiferromagnetic (Co,Fe)O thin film bilayers. The films were deposited onto amorphous SiO(2) and single crystalline MgO(110)/(100) substrates. Magnetometry showed that ion-beam bombardment was capable of modifying the coercivity and loop shape for the thin film system at room temperature, corresponding to alteration of the effective magneto-crystalline anisotropy field. After field cooling to 50 K, a shifted hysteresis loop was seen for those films containing a proportion of the antiferromagnetic rock-salt (Co,Fe)O phase, with an exchange bias magnitude that depended on the ion-beam bombardment conditions. Our results indicate that matching the substrate with appropriate ion-bombardment conditions provides a promising way to engineer selectively two important types of magnetic anisotropy in ferromagnetic/antiferromagnetic bilayers: magneto-crystalline and exchange bias. © 2012, Institute of Electrical and Electronics Engineers (IEEE)

Altering the exchange bias in Co90Fe10/(Co,Fe)O bilayers by changing the antiferromagnet's magnetism via interfacial ion-beam bombardment and different single crystalline MgO substrates

In this study, we investigated the exchange bias (coupling) effects in CoFe/(Co,Fe)O bilayers byusing different single crystal substrates of MgO(100) and MgO(110) and Ar ion-beambombardment on the surface of the bottom antiferromagnet (Co,Fe)O layer before capping withferromagnet CoFe. In the CoFe/(Co,Fe)O/MgO(110) bilayer, above the irreversibility temperature(Tirr. 170 K), there was a rapid decrease in M(T) with increasing temperature, unlike the CoFe/(Co,Fe)O/MgO(100) film that showed an increased Tirr. 300K and no observable decrease inM(T) above Tirr. The different M vs T zero-field-cooled/field-cooled behavior of the CoFe/(Co,Fe)O bilayers on MgO(100) and MgO(110) indicated that the FM CoFe spin orientationswere affected by the different substrates used via exchange coupling to the AF (Co,Fe)O layeraltered by MgO

The effects of single crystalline substrates and ion-beam bombardment of exchange-biased NiO/NiFe bilayers

Session RC: Structured Material

Exchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry

We investigated a hematite α-Fe2O3/permalloy Ni80Fe20 bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the Néel temperature of bulk α-Fe2O3 is known to be very high (860 K), we attribute the low-temperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5–1.0 μB per Fe atom within a depth of 1–2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains

Effect of ion-beam bombardment on microstructural and magnetic properties of Ni80Fe20/α-Fe2O3 thin films

This journal issue entitled: Microprocesses and NanotechnologyIon-beam bombardment has been established as an effective way to tune the microstructure and thus modify the magnetic anisotropy of thin film materials, leading to certain remarkable magnetic properties. In this work, we investigated a Ni80Fe20/α-Fe2O3 bilayer deposited with a dual ion-beam deposition technique. Low-energy argon ion-beam bombardment during the α-Fe2O3 deposition led to a decline of crystallinity and interfacial roughness of the bilayer, whereas the grain size distribution remained essentially unchanged. At low temperature, the coercivity exhibited a pronounced decrease after the bombardment, indicating that the effective uniaxial anisotropy in the ferromagnetic layer was dramatically reduced. Such reduction in uniaxial anisotropy was likely attributed to the irreversible transition in the α-Fe2O3 grains caused by the ion-beam bombardment, which subsequently modified the anisotropy in the Ni80Fe20 layer. The bombarded bilayer also exhibited a larger ΔMFC–ZFC compared to the un-bombarded bilayer, which indicated a stronger exchange coupling between the ferromagnetic layer and the antiferromagnetic layer

Modulating the magneto-crystalline anisotropy and the exchange bias field in CoFe/(Co,Fe)O bilayers using ion-beam bombardment and single crystalline substrates

We report the effects of ion-beam bombardment on the room temperature and low temperature magnetic properties of ferromagnetic CoFe/antiferromagnetic (Co,Fe)O thin film bilayers. The films were deposited onto amorphous SiO2 and single crystalline MgO (110)/(100) substrates. Magnetometry showed that ion-beam bombardment was capable of modifying the coercivity and loop shape for the thin film system at room temperature, corresponding to alteration of the effective magneto-crystalline anisotropy field. After field cooling to 50 K, a shifted hysteresis loop was seen for those films containing a proportion of the antiferromagnetic rock-salt (Co,Fe)O phase, with an exchange bias magnitude that depended on the ion-beam bombardment conditions. Our results indicate that matching the substrate with appropriate ion-bombardment conditions provides a promising way to engineer selectively two important types of magnetic anisotropy in ferromagnetic/antiferromagnetic bilayers: magneto-crystalline and exchange bias

Tailoring interfacial exchange coupling with low-energy ion beam bombardment: Tuning the interface roughness

By ascertaining NiO surface roughness in a Ni80Fe20/NiO film system, we were able to correlate the effects of altered interface roughness from low-energy ion-beam bombardment of the NiO layer and the different thermal instabilities in the NiO nanocrystallites. From experiment and by modelling the temperature dependence of the exchange bias field and coercivity, we have found that reducing the interface roughness and changing the interface texture from an irregular to striped conformation enhanced the exchange coupling strength. Our results were in good agreement with recent simulations using the domain state model that incorporated interface mixing. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3697405