Relaxation of thermo-remanent magnetization in Fe–Cr GMR multilayers

Abstract

The time decay of the thermo-remanent magnetization (TRM) in Fe-Cr giant magnetoresistive (GMR) multilayers has been investigated. The magnetization in these multilayers relaxes as a function of time after being cooled in a small magnetic field of 100 Oe to a low temperature and then the magnetic field is switched off. Low-field ðo500 OeÞ magnetization of these samples has shown history dependence. This spin-glass-like behavior may originate from structural imperfections at the interfaces and in the bulk. We find that the magnetization relaxation is logarithmic. Here the magnetic viscosity is found to increase first with increasing temperature, then it reaches a maximum around T g , and further it decreases with increasing temperature. This behavior is different from that of conventional spin glasses where the logarithmic creep rate is observed to increase with temperature. The dynamical effects of these multilayers are related to the relaxation of thermally blocked superparamagnetic grains and magnetic domains in the film layers. r

Interfacial disorder and magnetic frustration in epitaxial Fe/Cr/Fe trilayers studied by thermoremanent magnetization

“…We measured magnetization curves for all samples from -50 kOe to +50 kOe, and observed magnetic hysteresis with coercive forces (about 1 Oe for the samples of T s = 300 • C and 30 ∼ 100 Oe for T s = 400 • C) at 300 K for all samples, which indicates that our epitaxially grown Fe/Cr/Fe trilayers are ferromagnetic at least at 300 K. The result suggests that the internal disorder due to the interdiffusion can be almost disregarded in our samples because the transition temperature becomes lower far below room temperature when such a bulk-like frustration occurs [6,7]. Figure 4 shows time dependence of the TRM in each sample in the linear scale (a) and the logarithmic scale (b).…”

“…The direct observation of the slow dynamics is possible by measuring time dependence of the thermoremanent magnetization (TRM). As far as we know, time decay of the TRM has been measured only in a polycrystalline Fe/Cr system [6] or an epitaxial Fe/Cr with considerable interdiffusion [7] in which dominant origin of the frustration is not the interfacial disorder itself but that including substantial internal disorder. In fact, the magnetic transitions in such systems occur well below room temperature due to the bulk-like disorder [6,7].…”

“…As far as we know, time decay of the TRM has been measured only in a polycrystalline Fe/Cr system [6] or an epitaxial Fe/Cr with considerable interdiffusion [7] in which dominant origin of the frustration is not the interfacial disorder itself but that including substantial internal disorder. In fact, the magnetic transitions in such systems occur well below room temperature due to the bulk-like disorder [6,7]. In this study, in order to investigate the relaxation phenomena of Fe/Cr(001) system in which the interfacial disorder is essential, we prepared the epitaxial Fe/Cr/Fe(001) trilayers with various degrees of the interfacial flatness by using the molecular beam epitaxy (MBE) technique and measured the time dependence of the TRM.…”

Structural and Magnetic Properties of Fe50Cr50Alloys Prepared by Mechanical Alloying Method

“…Especially, the Fe-Cr layered magnetic materials were extensively studied for the application of magnetic devices [1][2][3][4][5], and the stainless Fe-Cr alloy has been used in various applications of the structural materials of fuel cells and fusion reactors [6]. The peculiarity of the Fe-Cr system is the existence of a wide miscibility gap in the phase diagram where both Fe and Cr are insoluble at room temperature.…”