Effective exchange coupling in permalloy-gadolinium films (original) (raw)
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Applied Physics A, 2005
We have studied the influence of the growth conditions on the structural characteristics of sputtered Py(Fe 20 Ni 80)/ Gd/Py(Fe 20 Ni 80) thin films. Auger electron spectroscopy reveals the existence of Ni in the Gd layer. The Ni concentration profile appears asymmetric with a higher concentration close to the top Py layer. This asymmetrical Ni concentration produces a different coercivity of each Py layer. It is possible to reduce the Ni interdiffusion by using multilayers based on Py/Gd bilayers separated by Mo spacers between the Py/Gd bilayers. In these samples we have obtained an enhancement of the structural and magnetic properties.
Domain walls and exchange-interaction in Permalloy/Gd films
New Journal of Physics, 2008
In this work we study the exchange coupling in Permalloy (Py)/gadolinium (Gd) bilayers. The exchange-coupled Py/Gd system is very temperature dependent and moreover the magnetization process in the Py layer is mainly due to domain wall (DW) displacements which are strongly controlled by pinning effects. We propose that this pinning could be caused by magnetostatic and exchange interactions between Py DWs and the magnetostrictive Gd layer. These effects mask the antiferromagnetic coupling between layers and, depending on temperature and Py thicknesses, apparent ferromagnetic coupling occurs. The study has been performed in the 80-300 K temperature range for different Py layer thicknesses and different Py induced anisotropies. Contents 1. Introduction 2 2. Experimental 3 3. Results and discussion 5 4. Conclusions 9 Acknowledgments 9 References 10
Enhanced exchange and reduced magnetization of Gd in an Fe/Gd/Fe trilayer
Physical Review B, 2011
The exchange interaction of Gd adjacent to Fe has been characterized by transport measurements on a double spin valve with a Fe/Gd/Fe trilayer as the middle layer. Our measurements show that the ferromagnetism of the Gd is enhanced by the presence of the Fe, and it remains ferromagnetic over its Curie temperature up to a thickness no smaller than 1 nm adjacent to the Fe. This thickness is more than double what has been reported before. Additionally, the saturation magnetization of the thin Gd layer sandwiched in Fe was found to be half of its bulk value. This reduced magnetization does not seem to be related to the proximity of Fe but rather to the incomplete saturation of Gd even for very high fields.
Enhanced interfacial magnetic coupling of Gd /Fe multilayers
Physical review letters, 2001
The spatial extent zeta(AFM) and strength J(AFM) of the antiferromagnetic (AFM) exchange coupling at buried Gd /Fe interfaces in ferrimagnetic [Gd(50 A)Fe(15,35 A)](15) sputtered multilayers is obtained from combined x-ray resonance magnetic reflectivity and magnetic circular dichroism measurements. zeta(AFM) is 4.1(7) A or approximately 1-2 interatomic distances in bulk Gd and Fe; J(AFM) is 1050(90) K, comparable to the ferromagnetic exchange in bulk Fe.
Peculiarities of ferrimagnetism of Gd/Co multilayers
Journal of Alloys and Compounds, 2001
The features of the ferrimagnetic ordering in multilayered Gd / Co films have been investigated with a torquemeter, vibrating sample and SQUID magnetometers, and ferromagnetic resonance. A phenomenological analysis of the possible mechanisms of magnetic interaction in these structures was made using the molecular field theory. The model of non-uniform interlayer exchange between Gd and Co layers has some advantages in comparison with the model of partial mixing of the layers.
Magnetic and structural properties of the Gd/Ni-Bilayer-System
Rare earth elements have been the scope of intensive research for many of their different properties over the past decades. The high magnetic permanent moment of these elements aroused a lot of interest and research on their magnetic behavior or structure, which was already conducted in the early 1970s. But due to the challenging problems associated with the handling of rare earths like their strong reactivity with water and oxygen, strong alloying with other metals or their high content of impurities was keeping research only to a small number of involved groups and publications per year. Another issue is the non-epitaxial or even amorphous growth of nearly all rare earth elements if evaporated under UHV conditions. There are only a few substrates which allow an epitaxial growth of gadolinium for example. But still the search for materials with high magnetization or either high or low coercivity for magnetic data storage technology or magnetic sensing elements attract notice to thi...
Magnetic Structures of an Iron–Gadolinium Multilayer at Low Temperatures
Japanese Journal of Applied Physics, 2002
Low-temperature magnetic structures of an [Fe/Gd] 15 multilayer are determined using the resonant X-ray magnetic scattering technique at a synchrotron source. The difference intensities of specular Bragg reflections observed by flipping the helicity of circularly polarized probing X-rays of energy close to the L 3 absorption edge of Gd show that the multilayer is in the Gdaligned state with the magnetic moments of the Gd layers oriented parallel to the applied in-plane field at H ¼ 0:5 kOe, T ¼ 10 K. This transforms into the twisted state with canted Gd moments by raising field strength H and/or temperature T. In the twisted state, the Gd moments at the interfaces and the core of the Gd layers show distinctive canting angles. Temperature and field-dependent in-plane rotations of local Gd moments have been visualized.
Magnetization dynamics in interlayer exchange-coupled in-plane/out-of-plane anisotropy bilayers
Physical Review B, 2009
The static and high-frequency properties of bilayer systems consisting in a single-crystal garnet film with a perpendicular anisotropy exchange coupled with a thin Permalloy film with a small in-plane anisotropy have been investigated both numerically and experimentally. The dynamic susceptibility spectra computed by means of two-dimensional micromagnetic simulations extended to stratified films reveal clearly the existence of multiple resonance lines resulting from the coupling between different magnetic area ͑domain walls, domains͒ inside the garnet film and the Permalloy film. In particular, exaltation of intensive domain wall resonances occurs within the frequency range including the uniform gyromagnetic mode of the Permalloy film. The effect of the garnet and Permalloy film thicknesses on the features of the dynamic susceptibility spectra is then studied. The experimental power absorption spectra recorded on a Permalloy/YIGBiLuAl-like bilayer exhibit well-defined resonance lines, most of them assigned to coupled modes of the bilayer nicely predicted by the micromagnetic simulations. The strong direct exchange coupling at the interface between the two layers appears as a predominant factor for this metal-oxide system.
Physical Review B, 2010
We demonstrate an exchange bias in (Ga,Mn)As induced by antiferromagnetic coupling to a thin overlayer of Fe. Bias fields of up to 240 Oe are observed. Using element-specific x-ray magnetic circular dichroism measurements, we distinguish a strongly exchange coupled (Ga,Mn)As interface layer in addition to the biassed bulk of the (Ga,Mn)As film. The interface layer remains polarized at room temperature. PACS numbers: 75.70.Cn, 75.50.Pp, 75.50.Bb Ferromagnetic (FM) semiconductors offer the prospect of combining high-density storage and gate-controlled logic in a single material. The realization of spin-valve devices from FM semiconductors requires the controlled switching of magnetization in adjacent layers between antiferromagnetic (AFM) and FM configurations. This has motivated several theoretical investigations of interlayer coupling in all-semiconductor devices 1 , and AFM coupling has recently been demonstrated in (Ga,Mn)As multilayers separated by p-type non-magnetic spacers 2 . However, the Curie temperature T C of (Ga,Mn)As is currently limited to 185 K in single layers 3 , and is typically much lower for layers embedded within a heterostructure 2 , which is an obstacle to the practical implementation of semiconductor spintronics.
Temperature dependence of ferromagnetic resonance in permalloy/NiO exchange-biased films
The European Physical Journal B, 2005
The temperature dependencies of the ferromagnetic resonance (FMR) linewidth and the resonance field-shift have been investigated for NiO/NiFe exchange-biased bilayers from 78 K to 450 K. A broad maximum in the linewidth of 500 Oe, solely due to the exchange-bias, is observed at ≈150 K when the magnetic field is applied along the film plane. When the magnetic field is applied perpendicular to the film plane, the maximum in the linewidth is less pronounced and amounts to 100 Oe at the same temperature. Such a behavior of the FMR linewidth is accompanied with a monotonic increase in the negative resonance field-shift with decreasing temperature. Our results are compared with the previous experimental FMR and Brillouin light scattering data for various ferromagnetic/antiferromagnetic (FM/AF) structures, and suggest that spin dynamics (spin-wave damping and anomalous resonance field-shift) in the FM/AF structures can be described in a consistent way by a single mechanism of the so-called slow-relaxation.