Size Effect in the Spin Glass Magnetization of Thin AuFe Films as Studied by Polarized Neutron Reflectometry

Abstract

We used polarized neutron reflectometry to determine the temperature dependence of the magnetization of thin AuFe films with 3% Fe concentration. We performed the measurements in a large magnetic field of 6 T in a temperature range from 295 to 2 K. For the films in the thickness range from 500 to 20 nm we observed a Brillouin-type behavior from 295 K down to 50 K and a constant magnetization of about 0.9 micro(B) per Fe atom below 30 K. However, for the 10 nm thick film we observed a Brillouin-type behavior down to 20 K and a constant magnetization of about 1.3 micro(B) per Fe atom below 20 K. These experiments are the first to show a finite-size effect in the magnetization of single spin-glass films in large magnetic fields. Furthermore, the ability to measure the deviation from the paramagnetic behavior enables us to prove the existence of the spin-glass state where other methods relying on a cusp-type behavior fail.

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

“…Within the errors the magnetization stays constant with a value of about 1 B per Fe atom. This deviation from the Brillouin function at temperatures below 50 K has also been observed in Au 97 Fe 3 films [8,9].…”

“…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].…”

“…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]. The present study is an extension of the previous work by focusing on the magnetic-field dependence of the spin glass film magnetization.…”

Magnetic and magnetocaloric properties of Dy5Pd2: role of magnetic irreversibility

“…33 On the other hand the FC magnetization is reversible. 34 In FC measurement the system goes to the near equilibrium state without further "minima hop". 4 We have calculated magnetic entropy change due to the application of an external magnetic eld in Dy 5 Pd 2 by using MXR also from the magnetization isotherms obtained by FCC and FCW protocols.…”

Anomalous random correlations of force constants on the lattice dynamical properties of disordered Au-Fe alloys

“…Due to the higher magnetic state of Fe in Au-Fe than in pure Fe, various properties have been studied, including thickness dependent spin-glass behavior and anomalous hall conductivity in Fe/Au multilayers. [1][2][3][4][5] Due to its exceptional biocompatibility and favorable physical properties, Au-Fe nanoparticles find various applications in medical sciences, as a promising candidate for cancer cell treatment, multimodal magneto-resonance imaging agent, etc.. [6][7][8][9][10] Gold-rich Au-Fe alloys form a simple face-centeredcubic (fcc) structure. Although fcc is a high-temperature phase, Au-Fe alloys up to 53 at.%Fe are reported to be easily stabilized at room temperature.…”