Spin Seebeck effect in Y-type hexagonal ferrite thin films

Abstract

Spin Seebeck effect (SSE) has been investigated in thin films of two Y-hexagonal ferrites Ba2Zn2Fe12O22 (Zn2Y) and Ba2Co2Fe12O22 (Co2Y) deposited by a spin-coating method on SrTiO3(111) substrate. The selected hexagonal ferrites are both ferrimagnetic with similar magnetic moments at room temperature and both exhibit easy magnetization plane normal to c-axis. Despite that, SSE signal was only observed for Zn2Y, whereas no significant SSE signal was detected for Co2Y. We tentatively explain this different behavior by a presence of two different magnetic ions in Co2Y, whose random distribution over octahedral sites interferes the long range ordering and enhances the Gilbert damping constant. The temperature dependence of SSE for Zn2Y was measured and analyzed with regard to the heat flux and temperature gradient relevant to the SSE signal.

Spin Seebeck effect in ɛ-Fe2O3 thin films with high coercive field

“…This is rather unexpected, since both Fe 3 O 4 and γ-Fe 2 O 3 phases, which are considered as possible secondary magnetic phases, were proved to exhibit significant spin Seebeck signal [27,28]. The accurate comparison of SSE measured by different laboratories is difficult, since in most of the experimental setups the temperature sensors measuring the temperature difference △T describes not merely the thermal characteristics of the studied layered material but the whole measurement cell instead, which makes the quantity in units of µV/K physically irrelevant to the SSE itself [29][30][31]. Nevertheless, as the SSE in ε-Fe 1−x Al x O 3 is about 10× smaller than in Fe 3 O 4 or γ-Fe 2 O 3 , so even taking into account this uncertainty, it could be expected that their presence should affect SSE signal similarly as magnetization.…”

Measurement of the heat flux normalized spin Seebeck coefficient of thin films as a function of temperature

“…In reports of low temperature SSE (LTSSE) measurements, either S∇ T is quoted or S J Q is estimated assuming that the power, Q, supplied to the heater passes through the sample without loss. [14][15][16] This is not reliable as low temperature thermal measurements are susceptible to multiple sources of heat loss and is compounded by the fact that it is often difficult to find low temperature heat flux sensors (HFSs). This is also true of measurements where a lithographically patterned on-chip heater is used, 17,18 which, although allowing for measuring the signals from smaller samples, do not allow for the accurate determination of S J Q .…”

“…Therefore, by applying Eqs. (14) and (15) to the data obtained from calibration mode (b) alongside the ratio, f, determined from calibration mode (a), the sensitivities of HFSs P 3 and P 4 can be determined as a function of temperature, as shown in Fig. 2(d).…”

“…In reports of low temperature SSE measurements either 𝑆 ∇𝑇 is quoted or 𝑆 J Q is estimated assuming that the power, 𝑄, supplied to the heater passes through the sample (without loss) 13,14,15 . This is not reliable as low temperature thermal measurements are susceptible to multiple sources of heat loss and is compounded by the fact that it is often difficult to find low temperature heat flux sensors.…”

Study of the Structural and Magnetic Properties of Co-Substituted Ba2Mg2Fe12O22 Hexaferrites Synthesized by Sonochemical Co-Precipitation

“…The T-block is made of four oxygen layers, with a barium atom substituting an oxygen atom in the inner two layers, which are opposite one another in the neighboring layers, resulting in two tetrahedral and six octahedral sites [15]. The easy magnetization axis lies in a plane perpendicular to the c axis direction, while the non-compensated magnetic moment lying in the ab plane arises from dominating majority spins in octahedral 3 a , 3 b , and 18 h sites and minority spins in tetrahedral 6 c T and 6 c S and octahedral 6 c sites [16]. These majority spins and minority spins determine the two magnetic sublattices different from crystal structural blocks— L m (spins in octahedral 3 a , 3 b , and 18 h sites) and S m (spins in tetrahedral 6 c T and 6 c S and octahedral 6 c sites) blocks alternating along [001], which bear, correspondingly, opposite large and small magnetization M [11].…”