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15 May 2002

Volume 91, Issue 10, pp. 6227-8917

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Monte Carlo simulations of ordering in ferromagnetic–antiferromagnetic bilayers

Shan-Ho Tsai, D. P. Landau, and Thomas C. Schulthess

J. Appl. Phys. 91, 6884 (2002); http://dx.doi.org/10.1063/1.1447868 (3 pages) | Cited 9 times

Online Publication Date: 13 May 2002

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Monte Carlo simulations have been used to study phase transitions on coupled anisotropic ferro/antiferromagnetic (FM/AFM) films of classical Heisenberg spins. We consider films of different thicknesses, with fully compensated exchange across the FM/AFM interface. We find indications of a phase transition on each film, occuring at different temperatures. It appears that both transition temperatures depend on the film thickness. © 2002 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions
75.10.Jm Quantized spin models, including quantum spin frustration

Magnetic force microscope study of antiferromagnet–ferromagnet exchange coupled films

Taras Pokhil, Dian Song, and Eric Linville

J. Appl. Phys. 91, 6887 (2002); http://dx.doi.org/10.1063/1.1452225 (3 pages) | Cited 9 times

Online Publication Date: 13 May 2002

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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 switching, just slight rippling of magnetization in the FM, was observed in the samples with an IrMn AFM layer. The results can be explained using either the model of thermally activated switching of AFM grains or the model of induced uniaxial anisotropy at the AFM/FM interface suggesting local variations of induced uniaxial anisotropy. In both models, the in-plane exchange in the FM layer has to be taken into account. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys

Magnetization reversal of exchange coupled CoFe/IrMn bilayers

Tong Zhao, Kunliang Zhang, and Hideo Fujiwara

J. Appl. Phys. 91, 6890 (2002); http://dx.doi.org/10.1063/1.1447185 (3 pages) | Cited 3 times

Online Publication Date: 13 May 2002

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The magnetization reversals of circular elements of CoFe/IrMn bilayers were studied using magnetic force microscopy. Drastic changes of domain structures and the nature of the reversal processes were observed with varying thickness of the CoFe layer. The localized incoherent rotation dominates in the reversal process when the CoFe layer is relatively thin while the domain wall motion dominates when the CoFe layer is thick. The effect of the competition between the distributed interfacial ferromagnet/antiferromagnet coupling and the coupling inside the ferromagnetic layer on the nature of the reversal process of the bilayers was investigated. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions

Investigation of exchange bias in FeMnC/FeMn bilayers

Hong-Wu Zhao, W. N. Wang, Y. J. Wang, W. S. Zhan, and J. Q. Xiao

J. Appl. Phys. 91, 6893 (2002); http://dx.doi.org/10.1063/1.1447186 (3 pages) | Cited 15 times

Online Publication Date: 13 May 2002

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The exchange bias (EB) effect and magnetic domain structures of FeMnC/FeMn bilayers prepared by a facing target sputtering system were studied. Unusual doubly shifted hysteresis loops were observed in a series of FeMnC/FeMn bilayers when different magnetic fields were applied to induce the exchange bias. The temperature dependences of the double shifted loops were measured and the ferromagnetic resonance measurement reveals the existence of EB. The correlation between the microscopic domain structures and the magnetization reversal processes was discussed, which suggests that the domain structure distribution of the antiferromagnetic layer is responsible for the loop shift. © 2002 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.70.Kw Domain structure (including magnetic bubbles and vortices)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Tuning exchange bias and coercive fields in ferromagnet/antiferromagnet bilayers with ion irradiation

J. Juraszek, J. Fassbender, S. Poppe, T. Mewes, B. Hillebrands, D. Engel, A. Kronenberger, A. Ehresmann, and H. Schmoranzer

J. Appl. Phys. 91, 6896 (2002); http://dx.doi.org/10.1063/1.1447187 (3 pages) | Cited 14 times

Online Publication Date: 13 May 2002

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The effect of He ion irradiation on the magnetic properties of NiFe exchange coupled to different antiferromagnetic alloys (FeMn, CrMn, and PtMn) with the same layer thickness is investigated. All systems exhibit an enhanced coercivity prior to irradiation. An exchange bias field is only observed for FeMn and PtMn. Upon ion irradiation the FeMn-based system shows with increasing ion dose an enhancement followed by a decrease and finally a full suppression of the exchange bias field. For systems exchange coupled to PtMn only a decrease and suppression of the bias field is found. This can be attributed to the ion induced chemical disordering of the antiferromagnetic phase in the latter case. In the case of CrMn the antiferromagnetic layer thickness is too small to induce an exchange bias field, but an enhanced coercivity is observed which is caused by the exchange coupling between the antiferromagnetic and ferromagnetic layers. For all systems, this enhanced coercivity of the exchange coupled bilayer system is modified by ion irradiation. © 2002 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
75.50.Ee Antiferromagnetics
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys

Exchange coupling in FeTaN/IrMn/FeTaN and NiFe/IrMn/NiFe trilayer films

H. S. Jung, W. D. Doyle, H. Fujiwara, J. E. Wittig, J. F. Al-Sharab, J. Bentley, and N. D. Evans

J. Appl. Phys. 91, 6899 (2002); http://dx.doi.org/10.1063/1.1447212 (3 pages) | Cited 12 times

Online Publication Date: 13 May 2002

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The dependence of the exchange bias field Heb in FeTaN/IrMn and NiFe/IrMn systems on the microstructure has been investigated. Bilayer and trilayer films of 50 nm thick FeTaN and NiFe and 10 nm thick IrMn were prepared by dc magnetron sputtering. The glass/FeTaN/IrMn/FeTaN trilayer showed that the top FeTaN did not influence Heb in the bottom FeTaN, closest to the substrate, during deposition and annealing. High-resolution transmission electron microscopy results showed limited evidence of epitaxial growth with both columnar single IrMn grains and multiple IrMn grains. In contrast, in the glass/NiFe/IrMn/NiFe trilayer, the top NiFe significantly influenced Heb in the bottom NiFe during deposition and annealing. X-ray diffraction data for both systems showed no detectable changes in either the crystallinity or (111) texture of the IrMn layer during annealing. In the NiFe system, the trend in Heb in the as-deposited and annealed states may be explained by assuming single columnar grains in the IrMn which couple the top and bottom NiFe layers. In the FeTaN system, the trend in Heb in the as-deposited state may be explained by assuming multiple IrMn grains which decouple the top and bottom FeTaN layers. However, the behavior on annealing is a mystery. © 2002 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology

Training effect in ferro (F)/antiferromagnetic (AF) exchange coupled systems: Dependence on AF thickness

K. Zhang, T. Zhao, and H. Fujiwara

J. Appl. Phys. 91, 6902 (2002); http://dx.doi.org/10.1063/1.1447869 (3 pages) | Cited 15 times

Online Publication Date: 13 May 2002

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Systematic investigation on the training effect in polycrystalline ferro (F)/antiferromagnetic (AF) exchange coupled systems using sputtered NiFe/IrMn bilayers has revealed that the type of the training effect changes from one type (Type I) to another (Type II) with increasing the AF layer thickness. In Type I the hysteresis loop in the pinned direction shrinks from both sides with the cycle of the applied field, while in Type II it shifts toward the positive pinned direction accompanied by loop shrinkage. This phenomenon can be understood as the stabilization of both AF grains contributing to the enhancement of coercivity and to the exchange biasing with cycles of applied field. This conclusion is based on our recently proposed extended Fulcomer and Charap’s model in which direct positive and negative exchange coupling between the AF grains is incorporated. © 2002 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys
68.65.Ac Multilayers

Exchange bias in (Pt/Co0.9Fe0.1)n/FeMn multilayers with perpendicular magnetic anisotropy

F. Garcia, G. Casali, S. Auffret, B. Rodmacq, and B. Dieny

J. Appl. Phys. 91, 6905 (2002); http://dx.doi.org/10.1063/1.1447870 (3 pages) | Cited 44 times

Online Publication Date: 13 May 2002

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We report the observation of exchange bias in (Pt/Co0.90Fe0.10)n/FeMn multilayers, with perpendicular magnetic anisotropy. We analyze the behavior of the exchange-bias field Heb as a function of temperature, FeMn thickness, number of (Pt/Co0.90Fe0.10) bilayers, and annealing conditions. Measurements carried out with field applied perpendicular to the plane of the samples indicate that the hysteresis loops present 100% of remanent magnetization, with Heb reaching 200 Oe and a tunable coercive field, depending on Co and Pt thickness ratio and on Pt buffer thickness. Furthermore, spin-valves of the form (Pt/Co0.90Fe0.10)n/NM/(Co0.90Fe0.10/Pt)m/Co0.90Fe0.10/FeMn with NM=Cu or Pt have been prepared. They exhibit two well separated hysteresis loops when the field is applied perpendicular to the plane. © 2002 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
68.65.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.05.Bx Metals, semimetals, and alloys
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