Heat diffusion in magnetic superlattices on glass substrates

Abstract

Pump-probe experiments and polarizing microscopy are applied to examine temperature and heat flow in metallic magnetic superlattices on glass substrates. A model of heat diffusion in thin layers for cylindrical symmetry, equivalent to the Green's function method, gives a good description of the results. The frequency dependence of temperature modulation shows that a glass layer should be added to the sample structure. The demagnetization patterns are reproduced with a Green's function that includes an interface conductance.Comment: 9 pages, 7 figure

Ultrafast demagnetization at high temperatures

“…The symmetric component S(τ ), obtained from measurements at different pump beam powers (figure 2), shows an overall offset S eq due to heat accumulation from multiple pulses [18], and a prominent peak, similar to results for Co films [23], with a step S step from one-pulse transients (figure 3). A Gaussian with a step function…”

“…The increase of equilibrium temperature above the room temperature at the center of the beam is T acc,max = 310 K for P abs = 40 mW, h = 4.1 nm, w 0 = 125 µm, an interface conductance G > 10 6 W/m 2 K and the same thermal parameters as in Ref. [18]. This gives a Curie temperature T C = 610 K, consistent with results in similar samples of T C = 800 K for Co/Pd [28] and T C = 600 K for Co/Pt [6].…”

“…Different conditions are present when thermal spin fluctuations are larger than UDM transients. In contrast to experiments at low repetition rates on thick and thermally-conducting films, heat accumulation from high repetition rate lasers and thin samples on thermally-insulating substrates enable local variation of the equilibrium temperature up to the Curie temperature [18]. In addition, a smaller transient signal compared to previous UDM experiments is obtained with smaller pulse energies, associated with the high repetition rate.…”

Demagnetizing fields in all-optical switching

“…The maximum heat accumulation is T acc,max = 310 K for P abs = 40 mW, h = 4.1 nm, w 0 = 125 µm, an interface conductance G > 10 6 W/m 2 K and the same thermal parameters as in Ref. [51].…”

All-optical switching in ferromagnetic superlattices.

“…2 | R(τ) for different magnetic fields and incident pump beam power.The film temperatures can be estimated for, , when neglecting the transfer of energy to the lattice over the duration of the pulse, where T 0 = 300 K is the initial temperature, C e = γT with γ = 665 J/(m 3 K 2 ) for bulk Co[65]. Similarly, the lattice temperature step increase after one pulse is T latt ≈ E pulse /( ℎ 0 2 ) ≈2.5 K. In addition, the heat accumulation temperature T acc cannot be neglected for thin samples and high-repetition rate lasers, with multiple pulses incident on the same area within the heat diffusion time 0 The maximum heat accumulation is T acc,max = 310 K for P abs = 40 mW, h = 4.1 nm, w 0 = 125 μm, an interface conductance G > 10 6 W/m 2 K and the same thermal parameters as in Ref [108]…”