A polarized neutron reflectometry study of the spin glass freezing in a 29nm thick AuFe film

Fritzsche, H.; Saoudi, Mouna; Temst, Kristiaan; Haesendonck, C. Van

doi:10.1016/j.physb.2007.02.020

Cited by 5 publications

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“…PNR has turned out to be an excellent tool to determine the absolute magnetic moment of single spin glass films avoiding the complications of multilayer samples such as inhomogeneity and an incomplete decoupling between the individual spin glass layers. In earlier PNR studies on Au 93 Fe 7 [6,7] and Au 97 Fe 3 films [8,9] we determined the temperature dependence of the absolute magnetic moment in a temperature range from 295 down to 2 K in a field of 6 T. Only recently we were able to show that the temperature dependence of the magnetization in AuFe films shows a size effect. The spin glass magnetization deviates from bulk behaviour below 10 nm but it still shows a typical spinglass behaviour [9].…”

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confidence: 99%

Magnetic field dependence of the magnetization of a 29 nm thick AuFe spin glass film

Saoudi

Temst

Haesendonck

et al. 2010

J. Phys.: Conf. Ser.

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Abstract. We performed polarized neutron reflectometry (PNR) experiments on a 29 nm thick Au 93 Fe 7 film. The measurements were done in a temperature range from 300 K to 2 K in a magnetic field up to 6 T applied in the sample's plane, at 2 K we took PNR data up to 11 T. The magnetization as determined by PNR can be described with a Brillouin function from 295 K down to 50 K assuming the magnetic moment of isolated Fe atoms, i.e. 4 B per Fe atom. Below 50 K the onset of the spin-glass freezing was observed as a strong reduction of the magnetic moment compared to the isolated Fe atom. IntroductionThe magnetic and transport properties of non-magnetic metals with magnetic impurities have been of large scientific interest for the last five decades, both for theorists and experimentalists [1]. The prerequisite for a spin glass is a competition among the different interactions between the spins with a random (glass-like) distribution of these interactions. The random spin arrangement in a spin glass is frozen when cooling the system below a certain temperature T f , called the freezing temperature. It is still under discussion whether the oscillating Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction is the only origin for this freezing or frustration. Khmelevskyi et al. [2] pointed out that the long-range RKKY interaction is not a prerequisite for a spin-glass system. They conclude that only very dilute systems can be described by the RKKY interaction properly, whereas for higher concentrations the magnetic properties in AuFe spin glass systems are dominated by short-range interactions.Depending on the concentration of the magnetic solute the AuFe system shows a very peculiar behaviour as a function of temperature. A paramagnetic to spin glass state is observed in the concentration range from 0.005 % to 10 at.% Fe [3], a paramagnetic to ferromagnetic phase transition for an Fe concentration above 10 at.% [3] and a reentrant spin-glass behavior in the range from 10 to 24 at.% [4]. An overview of bulk AuFe properties can be found in Cannella et al. [3].

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Section: Introductionmentioning

confidence: 99%

Magnetic field dependence of the magnetization of a 29 nm thick AuFe spin glass film

Saoudi

Temst

Haesendonck

et al. 2010

J. Phys.: Conf. Ser.

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“…20,21 We have successfully employed the technique of PNR to study the properties of thin AuFe spin glass films. 7,19,22 Recently we observed a finite-size effect in the temperature dependence of the magnetization of single Au 0.97 Fe 0.03 films. 7 The films in the range from 500 to 20 nm showed a Brillouin-type behavior from 295 K down to 50 K with a constant magnetization of 0.9 B per Fe atom below 30 K whereas the magnetization of the 10-nm-thick film could be fitted with a Brillouin function down to 20 K followed by a constant magnetization of 1.3 B .…”

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“…Susceptibility measurements showed that the cusp in AuFe samples is smeared out in magnetic fields 15 and anomalous Hall-effect measurements showed that the cusp vanishes in large magnetic fields. 3,18 Using polarized neutron reflectometry ͑PNR͒, we were able to show 7,19 that thin AuFe films show spin glass behavior in a large magnetic field of 6 T. Therefore, one has to be cautious when drawing conclusions from the vanishing of a cusp in either susceptibility or Hall-effect measurements.PNR has the advantage to measure the magnetization directly and the contribution of the substrate to the measured signal does not obscure the tiny signal of the thin film as has been shown, e.g., in ultrathin Fe films. 20,21 We have successfully employed the technique of PNR to study the properties of thin AuFe spin glass films.…”

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confidence: 98%

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“…At the same time, the Mo 0.7 Ge 0.3 layer acts as a diffusion barrier to avoid an interdiffusion of the AuFe film with the Si. Previous PNR experiments 7,19 were performed on AuFe samples that did not have this Mo 0.7 Ge 0.3 buffer layer. The films were analyzed using Rutherford backscattering and electron microprobe analysis showing that the thickness and composition were homogeneous.…”

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Loss of spin glass behavior in ultrathin AuFe films

et al. 2010

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We determined the temperature dependence of the magnetization of thin Au 97 Fe 3 films in the thickness range between 1 and 50 nm by performing polarized neutron reflectivity measurements in a magnetic field of 6 T in a temperature range from 200 down to 2 K. For the films in the thickness range from 50 to 2 nm, we observed a Brillouin-type behavior of noninteracting Fe atoms down to 50 K followed by a strong reduction compared to the Brillouin curve below 50 K. This reduction in the magnetization is a measure of the spin glass frustration and depends on the film thickness below 20 nm as shown in our previous study ͓M. Saoudi, H. Fritzsche, G. J. Nieuwenhuys, and M. B. S. Hesselberth, Phys. Rev. Lett. 100, 057204 ͑2008͔͒ on Au 97 Fe 3 films. The present study is a continuation of this work extending the thickness range down to 1 nm. It shows that below 10 nm, the reduction in the spin glass magnetization compared to a Brillouin-type behavior decreases with decreasing film thickness. Finally, the magnetization of the 1-nm-thick film could be described with a Brillouin function also below 50 K proving that ultrathin Au 97 Fe 3 layers below 1 nm do not show spin glass behavior anymore but are paramagnetic. Spin glass systems have been of interest to theorists as well as experimentalists for decades. 1 For thin films, the focus has been on finite-size effects, 2-8 the crossover from twoto three-dimensional behavior, 9 and the existence of a surface anisotropy. 8,[10][11][12][13][14] The challenge from an experimental point of view is to provide reliable experimental data on the magnetization of single films in the nanometer range containing only a few atomic percent of magnetic atoms in a nonmagnetic matrix.Superconducting quantum interference device magnetometry has been successfully employed to study bulk properties 15,16 but is not adequate to measure the magnetization of spin glass films in the nanometer range because of the small magnetic signal compared to the huge diamagnetic background of the substrate. Therefore, magnetometry experiments on thin spin glass films reported in literature were all performed on multilayers in order to increase the signal. 2,5 However, it is always questionable whether multilayer data represent the true single-film properties because of structural differences as the film gets thicker and an uncomplete decoupling of the individual spin glass layers. 17 Finite-size effects were also inferred from the vanishing of a cusp in anomalous Hall-effect measurements 3 of AuFe thin films at about 12 nm. However, the vanishing of a cusp does not necessarily mean a vanishing of the spin glass frustration. Susceptibility measurements showed that the cusp in AuFe samples is smeared out in magnetic fields 15 and anomalous Hall-effect measurements showed that the cusp vanishes in large magnetic fields. 3,18 Using polarized neutron reflectometry ͑PNR͒, we were able to show 7,19 that thin AuFe films show spin glass behavior in a large magnetic field of 6 T. Therefore, one has to be cautious when dra...

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