Effect of roughness, frustration, and antiferromagnetic order on magnetic coupling of Fe/Cr multilayers

Pierce, Daniel T.; Unguris, John; Celotta, Robert; Stiles, Mark D.

doi:10.1016/s0304-8853(99)00319-4

Cited by 160 publications

(92 citation statements)

References 83 publications

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“…Accordingly, the picture described for FM/AF bilayers [8] is different for closely coupled multilayers where interactions between multiple ferromagnetic (FM) layers and interactions between interfaces should be taken into account. Similar considerations also apply to the magneto-optic Kerr effect (MOKE) and scanning electron microscopy with polarization analysis (SEMPA) studies [17] on Fe/Cr/Fe trilayers and magnetization and ferromagnetic resonance studies of CoFe/Mn/CoFe trilayers [10], all of which specialize to a specific type of spacer layer and do not include the multilayer interactions responsible for our GAF behavior. Our results are thus complementary yet distinct from the results of bilayer/trilayer experiments.…”

Section: Pacs Numbers: 7570pamentioning

confidence: 99%

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Theodoropoulou

Hebard

Gabay

et al. 2003

Journal of Magnetism and Magnetic Materials

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Using temperature-dependent magnetoresistance and magnetization measurements on Fe/Cr multilayers that exhibit pronounced giant magnetoresistance (GMR), we have found evidence for the presence of a glassy antiferromagnetic (GAF) phase. This phase reflects the influence of interlayer exchange coupling (IEC) at low temperature (T < 140K) and is characterized by a field-independent glassy transition temperature, Tg, together with irreversible behavior having logarithmic time dependence below a "de Almeida and Thouless" (AT) critical field line. At room temperature, where the GMR effect is still robust, IEC plays only a minor role, and it is the random potential variations acting on the magnetic domains that are responsible for the antiparallel interlayer domain alignment. Given the established presence of GMR-based devices in technology, especially in the multi-billion dollar computer hard disk drive market, it may come as a surprise that there is still an incomplete scientific understanding of the GMR effect [1]. The mechanism for GMR, first observed in single crystalline (100) Fe/Cr multilayers grown by molecular beam epitaxy [2,3] and subsequently in magnetron-sputtered polycrystalline films[4], relies on spin-dependent scattering [5] and the associated dependence of resistance on the relative orientations of the magnetizations in neighboring layers. It is important to recognize that interlayer exchange coupling (IEC) is not necessarily required for a GMR effect [1]. In a particularly simple manifestation, two neighboring films, separated by a non-magnetic spacer layer, could have different coercive fields, thus giving rise to antiparallel alignment and a GMR effect, as the external field is cycled [6]. Randomness [7,8] and competing interactions such as biquadratic coupling [9,10] can also play a significant role. In this paper we identify a glassy antiferromagnetic (GAF) phase which by marking the influence of IEC at low temperatures implies that at higher temperatures random potential variations rather than IEC are responsible for antiparallel alignment.Our Fe/Cr multilayer samples have been prepared on silicon substrates by ion beam sputter deposition of separate Fe and Cr targets. Extensive characterization of the deposited multilayers showed distinct compositional and structural modulations with well-defined interfaces and a surface roughness on the order of 5Å. Ten and thirtylayer stacks with the repeat sequence [Fe(20Å)/Cr(d Cr )] are typically deposited and passivated with a 50Å-thick Cr layer. The Cr spacer thickness d Cr is varied over the range 8-12Å. The inset of Fig. 1 shows typical GMR traces at 300K and 10K for the magnetic field parallel to the planes of a [Fe(20Å)/Cr(12Å) ]×30 sample.In Fig. 1 we show a selected subset of temperaturedependent field-cooled (FC, open symbols) and zerofield-cooled (ZFC, closed symbols) magnetization data for a thirty layer sample with d Cr = 12Å and a GMR ratio ((R(0) − R(H))/R(0), Fig. 1 inset) of 20.6% at 10K. The data were taken using a SQUID magnetometer in fi...

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Section: Pacs Numbers: 7570pamentioning

confidence: 99%

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Theodoropoulou

Hebard

Gabay

et al. 2003

Journal of Magnetism and Magnetic Materials

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“…The period of the multilayer, being the sum of the individual layer thicknesses, is commonly in the nm range. The magnetic coupling in multilayer systems is shown to be strongly dependent on the layer thickness, the interface quality/roughness [5,6] and the lattice mismatch [7], which in turn can result in magnetic frustration and non collinear coupling [8,9]. The applicability of magnetic materials depends on how much control one has over these features.…”

Section: Magnetic Materialsmentioning

confidence: 99%

“…5 A simple magnetic multilayer is made of two alternating layers (of different materials), where at least one of them is ferromagnetic (FM). The period of the multilayer, being the sum of the individual layer thicknesses, is commonly in the nm range.…”

Section: Magnetic Materialsmentioning

confidence: 99%

Materials Design from First Principles : stability and magnetism of nanolaminates

Dahlqvist¹

2014

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The front cover image is a close up of M (red and blue spheres) and X (grey sphere) in M 2 AX. In the background its nanolaminated structure consisting of ordered, clustered, and disordered atoms or magnetic moments is illustrated.The spine image shows charge redistribution for an interstitial oxygen atom in Cr 2 AlC where blue indicate gain of electrons and red loss of electrons.The back cover image shows charge redistribution when oxygen substitutes for carbon in Ti 2 AlC where blue indicate gain of electrons and red loss of electrons. My daughter described it as "a planet, with water, and trees, and blue leaves". © Martin Dahlqvist, unless otherwise stated. Printed by LiU-Tryck, Linköping, Sweden, 2014 To my JETs ♥ v ABSTRACT In this thesis, first-principles calculations within density functional theory are presented, with a principal goal to investigate the phase stability of so called M n+1 AX n (MAX) phases. MAX phases are a group of nanolaminated materials comprised of a transition metal (M), a group 12-16 element (A), and carbon or nitrogen (X). They combine ceramic and metallic characteristics, and phase stability studies are motivated by a search for new phases with novel properties, such as magnetism, and for the results to be used as guidance in attempted materials synthesis in the lab.To investigate phase stability of a hypothetical material, a theoretical approach has been developed, where the essential part is to identify the set of most competing phases relative to the material of interest. This approach advance beyond more traditional evaluation of stability, where the energy of formation of the material is generally calculated relative to its single elements, or to a set of ad hoc chosen competing phases. For phase stability predictions to be reliable, validation of previous experimental work is a requirement prior to investigations of new, still hypothetical, materials. It is found that the predictions from the developed theoretical approach are consistent with experimental observations for a large set of MAX phases. The predictive power is thereafter demonstrated for the new phases Nb 2 GeC and Mn 2 GaC, which subsequently have been synthesized as thin films. It should be noted that Mn is used for the first time as sole M-element in a MAX phase. Hence, the theory is successfully used to find new candidates, and to guide experimentalists in their work on novel promising materials. Phase stability is also evaluated for MAX phase alloys. Incorporation of oxygen in different M 2 AlC phases are studied, and the results show that oxygen prefer different sites depending on M-element, through the number of available non-bonding M delectrons. The theory also predicts that oxygen substituting for carbon in Ti 2 AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x = 0.5) inMagnetism is a recently attained property of MAX phase materials, and a direct result of this Thesis work. We have demonstrated the importance of choice of magnetic spin configuration and elec...

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“…It is important to emphasize that, although the hysteresis loops of Pt/Fe and Cr/Fe are very similar, the mechanisms by which the Pt and Cr increase the interactions between islands are different for both materials: Pt is a paramagnetic material in which the coupling is related to the polarization of the interface region by the Fe islands and, in the case of the Cr, this element is an antiferromagnet in the bulk state that can couple the Fe islands via exchange interactions. Thus, the lower remanence values of the Cr/Feisland system could be related to frustration effects caused by the oscillatory nature of Fe-Cr-Fe coupling 1 in the complex Cr/Fe-island geometry ͑similar to the effect of roughness in Fe/Cr multilayers 35,36 ͒. A good probe of AF order in the Cr layers of Fe/Cr samples can be taken from exchange bias measurements, 37,38 that is, from the presence of a field shift of the hysteresis loop in materials composed of ferromagnetic-AF interfaces after a FC process from above the Néel temperature of the antiferromagnet.…”

Section: A Morphological and Magnetic Properties Of The Capped Fe Ismentioning

confidence: 99%

Magnetic order of Cr thin films in Nb/Cr/Fe-nanoisland hybrid: A comparative study between magnetic and superconducting properties

Navarro

Vélez

Huttel

et al. 2009

Journal of Applied Physics

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Shifted hysteresis loops characteristic of the exchange bias effect between a ferromagnet and an antiferromagnet are demonstrated in structures formed by a 2.5 nm Cr layer deposited on top of an array of Fe nanoislands (Cr/Fe-nanoislands). This effect evidences the persistence of antiferromagnetic (AF) order for Cr layers much thinner than the thickness reported in the literature. The field shift measured is found to increase for the smallest island sizes, which can be related with the enhancement of the Fe-nanoisland surface to volume ratio. The comparative study between superconducting proximity effects in Nb/Cr/Fe-nanoislands and Nb/normal metal/Fe-nanoisland hybrids (where the normal metals used are Al and Pt) confirms the presence of AF order in the 2.5 nm Cr spacer layer. A much shorter penetration depth of the Cooper pairs into the AF Cr layers than in the normal metal Pt and Al spacer layers is deduced.

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Effect of roughness, frustration, and antiferromagnetic order on magnetic coupling of Fe/Cr multilayers

Cited by 160 publications

References 83 publications

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

Materials Design from First Principles : stability and magnetism of nanolaminates

Magnetic order of Cr thin films in Nb/Cr/Fe-nanoisland hybrid: A comparative study between magnetic and superconducting properties

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