Magnetic characterization of exchange-coupled thin films having competing anisotropies (original) (raw)
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Magnetization depth dependence in exchange biased thin films
Applied Physics Letters, 2006
The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet (AF/FM) exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF2/FM (FM=Fe, Ni, and Py) bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature (T_N) is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T_N have also been discussed. The depth dependence of the magnetization has been studied in antiferromagnet/ferromagnet ͑AF/ FM͒ exchange coupled systems. Results from vector magnetometry and magneto-optical Kerr effect probing both the AF/FM and FM/air interfaces demonstrate the existence of a magnetization depth profile in FeF 2 /FM ͑FM= Fe, Ni, and Py͒ bilayers, contrary to the assumptions of most exchange bias models. The appearance of asymmetrical hysteresis loops below the AF Néel temperature ͑T N ͒ is explained by the creation of spring-like walls parallel to the AF/FM interface and the existence of incomplete domain walls. Changes in the reversal mechanism above T N have also been discussed.
Competing magnetic interactions in exchange-bias-modulated films
Physical Review B, 2010
The magnetization reversal in stripe-like exchange bias patterned Ni81Fe19/IrMn thin films was investigated by complementary inductive and high resolution magneto optical magnetometry, magneto optical Kerr microscopy, and polarized neutron reflectometry to clarify the effects of competing interfacial exchange bias and lateral interface contributions. Structures of varying ferromagnetic layer thickness and stripe period were analyzed systematically at the frozen-in domain state of oppositely aligned stripe magnetization. For all samples the mean magnetization of the magnetic hybrid structures was found to be aligned nearly orthogonally with respect to the stripe axis and the set exchange bias direction. Due to the interaction of interfacial coupling, exchange, and magneto-static energy contributions, the opening angle of neighboring stripe magnetizations increases with decreasing ferromagnetic layer thickness and increasing stripe period. The experimental observations are in agreement with an earlier proposed model for designing micro-patterned exchange bias films.
Nanomaterials
Here, we demonstrate the impact of ferromagnetic layer coating on controlling the magneto-optical response. We found that the transverse magneto-optical Kerr effect (TMOKE) signal and TMOKE hysteresis loops of Ni80Fe20 thin layers coated with a Cr layer show a strong dependence on the thickness of the Cr layer and the incidence angle of the light. The transmission and reflection spectra were measured over a range of incidence angles and with different wavelengths so as to determine the layers’ optical parameters and to explain the TMOKE behavior. The generalized magneto-optical and ellipsometry (GMOE) model based on modified Abeles characteristic matrices was used to examine the agreement between the experimental and theoretical results. A comprehensive theoretical and experimental analysis reveals the possibility to create a TMOKE suppression/enhancement coating at specific controllable incidence angles. This has potential for applications in optical microscopy and sensors.
Measurements of exchange anisotropy in NiFe/NiO films with different techniques
Journal of Applied Physics, 2000
One of the puzzles of the recent investigations on the exchange anisotropy in ferromagnetic (FM)I antiferromagnetic (AF) bilayers is the fact that different techniques yield different values for the exchange field (HE) between the layers. We report an in\.'estigation on sputtered NiFelNiO carried out with three different techniques, namely, magneto-optical Kerr effect magnetometry (MOKE), Brillouin light scattering (BLS), and ferromagnetic resonance (FMR). In an attempt to reconcile the measurements obtained with the various techniques, we interpret the data with a model that includes the formation of a planar domain wall in the AF layer, giving rise ,to a torque on the FM moment represented by an effective domain wall field (Hw). We find out that while the same pair of values of HE and Hw provide equally good fits to the reversible FMR and BLS measurements, different pairs are, necessary to fit the irreversible magnetometry data. © 2(}()() American Institute oj Physics.
Three-dimensional spin structure in exchange-biased antiferromagnetic/ferromagnetic thin films
Applied Physics Letters, 2009
A coexistence of lateral and in-depth domain walls in antiferromagnet/ferromagnet ͑AF/FM͒ thin films exhibiting double hysteresis loops ͑DHLs͒ is demonstrated. Comparison of single and DHLs together with local and global measurements confirms the formation of two oppositely oriented domains in the AF that imprint a lateral domain structure into the FM layer. Most significantly, the magnetization reversal mechanism within each opposite domain takes place by incoherent rotation of spring-like domain walls extending through the Ni thickness. Therefore, complex three-dimensional domain walls are created perpendicular and parallel to the AF/FM interface in exchange biased systems.
Magneto-optical Kerr Eect Study of Magnetic Anisotropy in Soft Ferromagnets
2014
The continued progress of modern information technology relies on understanding the influence of magnetic anisotropy on magnetic thin films. In this work, two sources of magnetic anisotropy are examined in two different soft ferromagnets: a uniaxial anisotropy induced during the fabrication of Ni80Fe20 and exchange anisotropy, or exchange bias, which occurs at the interface of Ni77Fe14Cu5Mo4/Fe50Mn50 bilayer. A home-built Magneto-optical Kerr effect magnetometer is used to measure the magnetic response of the soft ferromagnetic films and details of its construction are also discussed. A simple model of uniaxial anisotropy is described, then applied, to the uniaxial NiFe film and deviations from the model are critically analyzed. The exchange bias and coercive fields of NiFeCuMo/FeMn are reported for the first time and studied as a function of buffer layer material. The influence of the different buffer layer materials on the magnetization response of the bilayer is explained from a ...
Development of interface-induced out-of-plane magnetic anisotropy in Ni/Fe/Ni trilayers
Surface Science, 2001
The magnetic properties of trilayers Ni(1000 A)/ 57 Fe(x A)/Ni(200 A) grown by evaporation in ultra-high vacuum, have been investigated using M ossbauer spectroscopy, magneto-optic Kerr vector-magnetometry, and magnetic force microscopy (MFM). The data measured from a sample with Fe thickness x 6 A show the development of an out-ofplane anisotropy that tends to align the magnetization of the 57 Fe at about 40°respect to the normal to the layer plane. For higher 57 Fe layer thickness the data indicate that the magnetization lies in the ®lm plane. The magneto-optic measurements and the MFM images demonstrate also that when x 6 A the 57 Fe layer induces a reorientation of the magnetization of the Ni outermost layer from in-plane to out-of-plane. The results are interpreted as due to anisotropy eects induced at the interface Fe/Ni and to the c 3 a transition that takes place between 6 and 16 A.
Dependence of exchange bias in NiFe/NiO bilayers on film thickness
Here we report on the effect of the ferromagnetic (FM) and antiferromagnetic (AF) films thicknesses on the exchange bias field in a FM/AF bilayer. For this, a series of NiFe(t NiFe)/NiO(t NiO) bilayers were grown by DC magnetron sputtering onto commercial Si(001) wafers. Magneto-optical hysteresis loops were used as probes to measure the exchange-bias field, and the coercivity field, as functions of the in-plane angle, ϕH , and the films' thicknesses, tNiFe and tNiO. The in-plane symmetry of the exchange field and coercivity display unidirectional and uniaxial anisotropies, with angular dependences different from the simple cos ϕ H and cos 2 ϕ H , respectively. These symmetries are intrinsically sensitive to the thickness of both NiFe and NiO layers. With respect to the FM layer thickness, the exchange bias and coercivity field follow the usual 1/t NiFe , while the dependence on the thickness of the AF layer is more complicated, and is characterized by a critical behavior.
Thickness-dependent magnetic properties of Ni81Fe19, Co90Fe10 and Ni65Fe15Co20 thin films
Journal of Magnetism and Magnetic Materials, 2002
We present results of magnetization and magnetic anisotropy measurements in thin magnetic films of the alloys Ni 81 Fe 19 ; Co 90 Fe 10 and Ni 65 Fe 15 Co 20 that are commonly used in magnetoelectronic devices. The films were sandwiched between layers of Ta. At room temperature the critical thickness for all the films to become ferromagnetic is in the range 11-13 ( A. In Co 90 Fe 10 the coercivity and the anisotropy field both depend strongly on layer thickness. r 0304-8853/02/$ -see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 -8 8 5 3 ( 0 2 ) 0 0 5 7 7 -2