Broken ergodicity, memory effect, and rejuvenation in Taylor-phase and decagonalAl3(Mn,Pd,Fe)complex intermetallics

Abstract

The Taylor-phase complex intermetallic compound T-Al 3 Mn, its solid solutions with Pd and Fe, T-Al 3 ͑Mn, Pd͒ and T-Al 3 ͑Mn, Fe͒, and the related decagonal d-Al-Mn-Fe quasicrystal belong to the class of magnetically frustrated spin systems that exhibit rich out-of-equilibrium spin dynamics in the nonergodic phase below the spin-freezing temperature T f . Performing large variety of magnetic experiments as a function of temperature, magnetic field, aging time t w , and different thermal histories, we investigated broken-ergodicity phenomena of ͑i͒ a difference in the field-cooled and zero-field-cooled susceptibilities, ͑ii͒ the frequencydependent freezing temperature, T f ͑͒, ͑iii͒ hysteresis and remanence, ͑iv͒ ultraslow decay of the thermoremanent magnetization, ͑v͒ the memory effect ͑a state of the spin system reached upon isothermal aging can be retrieved after a negative temperature cycle͒, and ͑vi͒ "rejuvenation" ͑small positive temperature cycle within the nonergodic phase erases the effect of previous aging͒. We show that the phenomena involving isothermal aging periods ͑the memory effect, rejuvenation, and the ultraslow decay of the thermoremanent magnetization͒ get simple explanation by considering that during aging under steady external conditions, localized spin regions quasiequilibrate into more stable configurations, so that higher thermal energy is needed to destroy these regions by spin flipping, as compared to the thermal energy required to reverse a frustrated spin in a disordered spin-glass configuration that forms in the case of no aging. Common to all the investigated brokenergodicity phenomena is the slow approach of a magnetically frustrated spin system toward a global equilibrium, which can never be reached on accessible experimental time scales due to macroscopic equilibration times.

Anisotropic physical properties of the Taylor-phaseT-Al72.5Mn21.5Fe6.0com

“…The electrical resistivity and the Hall coefficient of the polygrain T-Al 3 Mn, T-Al 73 Mn 27−x Fe x ͑x =2,4͒ and the decagonal quasicrystal d-Al 73 Mn 21 Fe 6 were reported as well. 17 We also mention that the single crystal of composition Al 72.5 Mn 21.5 Fe 6.0 pertinent to this study was a Taylor phase, whereas the polycrystalline material of almost identical composition Al 73 Mn 21 Fe 6 reported in the preceding papers 15,17 was a decagonal quasicrystal. As discussed above, different annealing conditions may be the reason for this discrepancy.…”

“…Recently we have reported 15 the magnetic properties of a polygrain binary T-Al 3 Mn and a ternary T-Al 3 ͑Mn, Pd͒ and T-Al 3 ͑Mn, Fe͒ series of samples of compositions T-Al 73 Mn 27−x Pd x ͑x =2,4,6͒ and T-Al 73 Mn 27−x Fe x ͑x =2,4͒ and the decagonal quasicrystal d-Al 73 Mn 21 Fe 6 . All samples exhibited a pronounced magnetic memory effect that has lead to the application of this material for the thermal storage of digital information, serving as a new kind of a digital memory element-a thermal memory cell, 16 where the digital information is stored into the bulk of the material by pure thermal manipulation, in the absence of any electric, magnetic, or electromagnetic field.…”

“…Fe 6 were reported recently in a comprehensive study. 15 The results can be summarized as follows. ͑1͒ All samples show a transition to a spin-glass-type nonergodic phase at the spin-freezing temperature T f Ϸ 20-23 K, where below T f , the zero-fieldcooled ͑zfc͒ and field-cooled ͑fc͒ magnetic susceptibilities become unequal.…”

“…6͒ decagonal approximants, also belonging to the Al 13 TM 4 class of intermetallics, but comprising four atomic layers within one periodic unit of Ϸ0.8 nm along the stacking direction and a larger unit cell containing 102 atoms. The third was the Al 4 ͑Cr, Fe͒ compound with composition Al 80 Cr 15 Fe 5 ,7,8 belonging to the class of orthorhombic Al 4 TM phases first described by Deng et al, 9 which are approximants to the decagonal phase with six atomic layers in a periodic unit of 1.25 nm and 306 atoms in the giant unit cell. Common to all these phases are strongly anisotropic magnetic, electrical, and thermal transport properties between the stacking and the in-plane directions, where the crystals show the highest conductivity for both the electricity and heat along the stacking direction ͑corresponding to the periodic tenfold direction in d-QCs͒, whereas the in-plane anisotropy is considerably smaller, yet significant.…”

Hall effect in Taylor-phase and decagonal Al3(Mn,Fe) complex intermetallics

“…2 we present the magnetic susceptibility of our Al 73 Mn 27Àx Fe x samples as a function of temperature. These materials belong to the class of magnetically-frustrated spin system [5]. Spin-freezing temperatures of all the samples are well below those of interest for the separation of R 0 and R S .…”