scholarly journals Magnetic Exchange-Coupling In Copt/Co Bilayer Thin Films

1999 ◽  
Vol 562 ◽  
Author(s):  
J. Kim ◽  
K. Barmak ◽  
L. H. Lewist ◽  
D. C. Crewt ◽  
D. O. Welcht
Keyword(s):  
Exchange Coupling ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Magnetic Exchange ◽  
Two Phase ◽  
Soft Phase ◽  
Sputter Deposited ◽  
Equiatomic Alloy ◽  
Fcc Phase ◽  
Soft Composite

ABSTRACTThin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700°C and fully transformed from the FCC phase to the magnetically hard, ordered LI0 phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8–225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.

scholarly journals Magnetic Exchange-Coupling in CoPt/Co Bilayer thin Films

1999 ◽  
Vol 577 ◽  
Author(s):  
J. Kim ◽  
K. Barmak ◽  
L. H. Lewis ◽  
D. C. Crewt ◽  
D. O. Welcht
Keyword(s):  
Exchange Coupling ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Magnetic Exchange ◽  
Two Phase ◽  
Soft Phase ◽  
Sputter Deposited ◽  
Equiatomic Alloy ◽  
Fcc Phase ◽  
Soft Composite

ABSTRACTThin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700°C and fully transformed from the FCC phase to the magnetically hard, ordered L1 0 phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8-225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.

Giant Magnetoresistance in As-Sputter-Deposited Au/NiFe Multilayer Thin Films

1994 ◽  
Vol 343 ◽  
Author(s):  
W. Y. Lee ◽  
G. Gorman ◽  
R. Savoy
Keyword(s):  
Thin Films ◽  
Exchange Coupling ◽  
Giant Magnetoresistance ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Multilayer Films ◽  
Antiferromagnetic Coupling ◽  
Multilayer Thin Films ◽  
Glass Substrates ◽  
Sputter Deposited

ABSTRACTGiant magnetoresistance with low saturation fields (Hs’s) is reported in Au and permalloy (Ni0.82Fe0.18) or Co-doped permalloy multilayer thin films as-deposited on Ta-overcoated Si and glass substrates. A ΔR/R as high as 4.0% with ≈25 Oe Hs was observed at 295 K for the film consisting of 10 layers of 24 Å Au/13 Å Ni0.82Fe0.18 deposited on a 3 Å Ta-overcoated glass at 50 °C. A Hs value as low as ≈20 Oe with a 15% smaller ΔR/R has been observed for the films with a thicker (e.g., 50 Å) Ta underlayer. Magnetic hysteresis loops of these films indicate the presence of antiferromagnetic exchange coupling between the Ni0.82Fe0.18 layers. This exchange coupling is much smaller for the multilayer films without the Ta underlayer, resulting in a 6x smaller ΔR/R and lOx larger Hs observed for these films. Results of x-ray diffraction analysis indicate stronger (111) texturing for the multilayer films with a Ta underlayer, consistent with the stronger antiferromagnetic coupling between the the Ni0.82Fe0.18 layers in the film. The addition of 2–10 % Co moderately increases the ΔR/R value, but also increases substantially the Hs (up to ≈200 Oe).

Magnetic Exchange Effects in {CrIII2DyIII2} Single Molecule Magnets Containing Alcoholamine Ligands

2014 ◽  
Vol 67 (11) ◽  
pp. 1581 ◽  
Author(s):  
Stuart K. Langley ◽  
Daniel P. Wielechowski ◽  
Boujemaa Moubaraki ◽  
Brendan F. Abrahams ◽  
Keith S. Murray
Keyword(s):  
Single Molecule ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Magnetic Studies ◽  
Single Molecule Magnets ◽  
Magnetic Exchange ◽  
Bridging Ligands ◽  
Metallic Core ◽  
Ligand Coordination ◽  
Magnetic Hysteresis Loops

The synthesis and magnetic characterisation of four new heterometallic {CrIII2DyIII2} complexes 2–5 are described. The present work follows on from a recently isolated complex [CrIII2DyIII2(OMe)2(O2CPh)4(mdea)2(NO3)2] (1) (mdeaH2 = N-methyldiethanolamine), which displayed impressive single molecule magnet (SMM) properties, notably highly coercive magnetic hysteresis loops below 3.5 K. Compounds 1–5 all display a planar butterfly type metallic core arrangement, with the DyIII ions occupying the central body positions and the CrIII ion the outer wing positions. The core is stabilized by the amine–diolate, and carboxylate bridging ligands. Variation of the amine–diolate ligand resulted in several structural analogues which maintain the same metallic core, but differ from the parent 1 in the outer ligand coordination environment. Magnetic studies reveal complexes 2–5 also display SMM behaviour, unambiguously confirmed via low temperature magnetic hysteresis loops, each displaying wide coercive fields, a rare occurrence for lanthanoid-based SMMs.

Oscillatory Angular Dependence of Exchange Bias for Epitaxial NiO-Co (001) Bilayers

2001 ◽  
Vol 674 ◽  
Author(s):  
S. Dubourg ◽  
J.F. Bobo ◽  
B. Warot ◽  
E. Snoeck ◽  
J.C. Ousset
Keyword(s):  
Magnetic Field ◽  
Exchange Bias ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Field Application ◽  
Zero Field ◽  
Sign Change ◽  
Realistic Description ◽  
Sputter Deposited ◽  
The Magnetic Field

ABSTRACTWe have sputter-deposited NiO-Co bilayers on MgO (001) substrates. NiO grows epitaxially on MgO at 900°C and subsequently the room deposited 80 Åthick Co films have a fcc crystal structure in epitaxy with the oxide underlayer. These samples were warmed up to 300° C and then zero-field or field cooled through the NiO Néel temperature (a 300 Oe magnetic field was applied along the [100] or the [110] MgO axis). Magnetic hysteresis loops were obtained by magneto-optical Kerr effect, the magnetic field being oriented in the plane of the substrate for various angles α with respect to the [100] direction. The usually expected behavior for such experiments is a smooth angular α dependence of the exchange bias HE close to a cosine with only one sign change over 180°. The high crystallographic coherence of our NiO/Co bilayers induces a very unusual oscillatory HE (α) dependence with several sign changes according to the NiO axis field application. Despite of the Co magnetization switching mechanism which is not a pure coherent rotation, we propose a Stoner-Wohlfhart model including four fold anisotropy and unidirectional exchange anisotropy giving a realistic description of these typical magnetic properties.

Research on Magnetic Properties of Nd2Fe14B/α-Fe/Nd2Fe14B Exchange-Coupled Trilayer Films

2011 ◽  
Vol 84-85 ◽  
pp. 567-571
Author(s):  
Min Gang Zhang ◽  
Li Li Yang ◽  
Yi Chao Zhao ◽  
Jia Zhang ◽  
Gang Sun
Keyword(s):  
Exchange Coupling ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Maximum Energy ◽  
Soft Magnetic ◽  
Coupling Region ◽  
Magnetic Hysteresis Loops ◽  
Complete Exchange ◽  
Energy Products ◽  
The Relationship

The magnetic hysteresis loops of Nd2Fe14B/α-Fe/Nd2Fe14B exchange-coupling trilayer film are simulated by micromagnetic theory, and the relationship between remanence, coercivity, energy products and soft magnetic thickness are discussed in detail. The results show that the hysteresis loops is rectangle and the trilayer films are in complete exchange-coupling region when the soft magnetic thickness is below the critical point(5nm); With the increase of the soft magnetic thickness, the coercivity of the trilayer films decreases monotonically. Maximum energy products are obtained when the soft magnetic thickness is 5nm.

scholarly journals DFT Investigations of the Magnetic Properties of Actinide Complexes

2019 ◽  
Vol 5 (1) ◽  
pp. 15 ◽  
Author(s):  
Lotfi Belkhiri ◽  
Boris Le Guennic ◽  
Abdou Boucekkine
Keyword(s):  
Magnetic Properties ◽  
Exchange Coupling ◽  
Density Functional ◽  
Magnetic Hysteresis ◽  
Molecular Magnets ◽  
Blocking Temperature ◽  
Magnetic Exchange ◽  
Hartree Fock ◽  
Magnetic Exchange Coupling ◽  
Metal Metal

Over the past 25 years, magnetic actinide complexes have been the object of considerable attention, not only at the experimental level, but also at the theoretical one. Such systems are of great interest, owing to the well-known larger spin–orbit coupling for actinide ions, and could exhibit slow relaxation of the magnetization, arising from a large anisotropy barrier, and magnetic hysteresis of purely molecular origin below a given blocking temperature. Furthermore, more diffuse 5f orbitals than lanthanide 4f ones (more covalency) could lead to stronger magnetic super-exchange. On the other hand, the extraordinary experimental challenges of actinide complexes chemistry, because of their rarity and toxicity, afford computational chemistry a particularly valuable role. However, for such a purpose, the use of a multiconfigurational post-Hartree-Fock approach is required, but such an approach is computationally demanding for polymetallic systems—notably for actinide ones—and usually simplified models are considered instead of the actual systems. Thus, Density Functional Theory (DFT) appears as an alternative tool to compute magnetic exchange coupling and to explore the electronic structure and magnetic properties of actinide-containing molecules, especially when the considered systems are very large. In this paper, relevant achievements regarding DFT investigations of the magnetic properties of actinide complexes are surveyed, with particular emphasis on some representative examples that illustrate the subject, including actinides in Single Molecular Magnets (SMMs) and systems featuring metal-metal super-exchange coupling interactions. Examples are drawn from studies that are either entirely computational or are combined experimental/computational investigations in which the latter play a significant role.

A novel and facile route to in-situ formation of composites with dual coupling interactions for considerable millimeter-wave absorption performance

2021 ◽  
Author(s):  
Chuyang Liu ◽  
Tao Jiang ◽  
Tian Gao ◽  
Guangxian Xia ◽  
Yufan Cao ◽  
...  
Keyword(s):  
Millimeter Wave ◽  
Exchange Coupling ◽  
Ferromagnetic Coupling ◽  
Soft Magnetic ◽  
Magnetic Exchange ◽  
Magnetic Exchange Coupling ◽  
Absorption Performance ◽  
In Situ Formation ◽  
Facile Route

It is well known that both hard/soft magnetic exchange-coupling and ferroelectric-ferromagnetic coupling could facilitate the microwave absorption behavior. Herein, we propose the BaZrxFe12-xO19/Fe3O4/BaZrO3 composites to integrate the advantages of the...

scholarly journals Transferrable property relationships between magnetic exchange coupling and molecular conductance

2020 ◽  
Vol 11 (42) ◽  
pp. 11425-11434
Author(s):  
Martin L. Kirk ◽  
Ranjana Dangi ◽  
Diana Habel-Rodriguez ◽  
Jing Yang ◽  
David A. Shultz ◽  
...  
Keyword(s):  
Exchange Coupling ◽  
Semiquinone Radical ◽  
Magnetic Exchange ◽  
Magnetic Exchange Coupling ◽  
Coupling Parameters ◽  
Molecular Conductance

Calculated conductance through Aun–S–Bridge–S–Aun constructs are compared to experimental magnetic exchange coupling parameters in TpCum,MeZn(SQ–Bridge–NN) complexes, where SQ = semiquinone radical and NN = nitronylnitroxide radical.

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