**2.2 Growth techniques**

A variety of techniques are used to grow BaM thin films, including pulsed laser deposition (PLD) [8–10], alternating target laser ablation deposition (ARLAD) [11, 12], molecular beam epitaxy (MBE) [13], liquid phase epitaxy (LPE) [14, 15], magnetron sputtering [16, 17], and so on. Guo et al. at Boston Applied Technologies proposed a chemical solution deposition process to deposit BaM. Song and his colleagues succeeded in the PLD growth of BaM thin films that showed an FMR linewidth as narrow as single-crystal BaM bulks. However, these films showed a remanent magnetization much smaller than the saturation magnetization [9]. This problem was improved in the later experiments when tuning the deposition conditions [18]. **Figure 2** shows the PLD parameters which decide the thin film quality. **Figure 2b** shows that *c*-axis out-of-plane BaM grains can be grown on (0001) Al2O3 substrates; *c*-axis in-plane BaM grains can be grown on (11 20) Al2O3 substrates. A typical procedure is as follows: the oxygen pressure is set at 300 mTorr, and the substrate is heated to 800°C. The substrate-to-target separation is fixed at 4 cm, and the energy fluence of the laser beam is set to 0.7 J/cm<sup>2</sup> . The laser pulse repetition rate is increased from 1 to 5 pulse(s) per second in five equal steps over the first 5 min and is then set to 10 pulses/s for the remaining deposition. After the

#### **Figure 2.**

*Growth condition in pulsed laser deposition of BaM thin films. (a) Parameters controlling the BaM thin film quality. (b) Different Al2O3 substrate types for growing BaM with different* c*-axis orientations.*

anisotropy field of 17 kOe, which is along the *c* axis. This comes from the trigonal bipyramidal site Fe3+ ions, as well as breaking crystal symmetry in the R/R\* blocks. This is the most distinguished property of BaM, because the perpendicular anisotropy field originates from bulk intrinsic anisotropy. BaM has a large *c* constant of

temperature of bulk BaM is 725 K, which is much higher than the room tempera-

A variety of techniques are used to grow BaM thin films, including pulsed laser deposition (PLD) [8–10], alternating target laser ablation deposition (ARLAD) [11, 12], molecular beam epitaxy (MBE) [13], liquid phase epitaxy (LPE) [14, 15], magnetron sputtering [16, 17], and so on. Guo et al. at Boston Applied Technologies proposed a chemical solution deposition process to deposit BaM. Song and his colleagues succeeded in the PLD growth of BaM thin films that showed an FMR linewidth as narrow as single-crystal BaM bulks. However, these films showed a remanent magnetization much smaller than the saturation magnetization [9]. This problem was improved in the later experiments when tuning the deposition conditions [18]. **Figure 2** shows the PLD parameters which decide the thin film quality. **Figure 2b** shows that *c*-axis out-of-plane BaM grains can be grown on (0001) Al2O3 substrates; *c*-axis in-plane BaM grains can be grown on (11 20) Al2O3 substrates. A typical procedure is as follows: the oxygen pressure is set at 300 mTorr, and the substrate is heated to 800°C. The substrate-to-target separation is fixed at 4 cm, and

rate is increased from 1 to 5 pulse(s) per second in five equal steps over the first 5 min and is then set to 10 pulses/s for the remaining deposition. After the

*Growth condition in pulsed laser deposition of BaM thin films. (a) Parameters controlling the BaM thin film*

*quality. (b) Different Al2O3 substrate types for growing BaM with different* c*-axis orientations.*

. The Curie

. The laser pulse repetition

23.2 Å and an *a* constant of 5.89 Å. The *x*-ray density is about 5.29 g/cm<sup>3</sup>

ture. The exchange constant is 6.4 <sup>10</sup><sup>7</sup> erg/cm [7].

*Magnetic Materials and Magnetic Levitation*

the energy fluence of the laser beam is set to 0.7 J/cm<sup>2</sup>

**2.2 Growth techniques**

**Figure 2.**

**40**

deposition, the substrate is cooled down at a rate of 2°C/min in 400 Torr oxygen. The sample is then annealed at 850°C for 4 h in a standalone tube furnace, with a heating rate of 10°C/min and a cooling rate of 2°C/min.
