Aging and memory in a superspin glass

Memory effect and spin-glass-like behavior in Co-Ag granular films

“…In a typical dc memory experiment, one should follow a stop-and-wait protocol consisting of three steps: 14,24 ͑a͒ cool the sample in a zero-field at a constant rate from a temperature, T H , which is much higher than T p , the peak temperature of ZFC curves; ͑b͒ stop the cooling process at a temperature, T w , below T p and wait for t w ͑=6 h, in our experiments͒ and then resume the cooling process down to T base ͑=5 K in our experiments͒; ͑c͒ apply a small field at T base and measure the magnetization with increasing temperature up to T H . The difference between the stop-and-wait ZFC curve and a reference ZFC curve ͑without stopping at T w ͒ at the temperature T w can be attributed to the memory effect.…”

“…28͒ and Co-Cu ͑Ref. 29͒ granular films, and the memory effect in FeCo-Al 2 O 3 discontinuous multilayers, 24 we report on the memory effect in metallic, magnetic granular films.…”

“…To our best knowledge, the SGL phase has been mainly observed in some special particle systems, such as the magnetic frozen fluid composed of ␥-Fe 2 O 3 , -Fe 3 N, and Fe x C 1−x particles, [3][4][5]7 and a discontinuous ͓Co 80 Fe 20 ͑0.9 nm͒ /Al 2 O 3 ͑3 nm͔͒ 10 multilayer. 24 In these samples, there is probably a surface layer on the particles that does not have the same magnetic state as the particle core and may exhibit SGL behavior. 22,23 Therefore, one may ask what is the origin of spin-glass-like phenomenon in lowtemperature interacting nanoparticle systems.…”

Collective states of interacting ferromagnetic nanoparticles

“…Here the sample is rapidly cooled down in zero field to a temperature below T g and a certain waiting time, t w , spent at this temperature. Finally, a small field is applied and the magnetization recorded as function of time, t. Then the derivative S(t) = (1/µ 0 H)(∂M(t)/∂ ln t) shows a peak at t ≈ t w [2,9,22]. Hence, the system "remembers" the time spent in zero field before the field is applied.…”

Memory effects in a nanoparticle system: Low-field magnetization and ac susceptibility measurements

“…[2][3][4][5][6] Different experimental approaches have been employed to observe the memory effect in spin-glass system and particle systems. [2][3][4][5][6][7][8][9][10] The most acceptable experimental approaches for observing the memory effect include low frequency ac susceptibility 2-8 ͑ = Ј+ Љ͒ and low field dc magnetization measurements. 5,6,9,10 The experimental details for each approach are briefly described as the following.…”