**2. Experimental**

A target such as Nd-Fe-B, Pr-Fe-B, Sm-Co, and Fe-Pt was ablated with an Nd-YAG pulse laser with a wavelength of 355 nm together with a frequency of 30 Hz in a vacuum atmosphere. The chamber was evacuated to approximately 4 × 10−5 Pa with a vacuum equipment before the deposition. During the deposition, each target was rotated and the distance between the target and the substrate (*T-S* distance) varied from 5 to 20 mm. In the experiment, a laser power was measured with a power meter in front of the entrance lens of the chamber. The laser energy density (LED) varied by controlling the laser power (LP) together with a spot size of laser beam which could be changed by moving the distance between the focal lens and the target intentionally (see **Figure 1**). Here, the spot size was expressed as a defocusing rate (DF rate) = (TD − FD)/FD × 100(%), where TD is the distance between the condensing lens and the target and FD is the focal length. In the experiment, the control of the defocusing rate (DF rate) enabled us to change LED widely compared with the variation of LP.

In some experiments, the post-annealing of a conventional annealing (CA) and a pulse annealing (PA), respectively, was carried out as shown in **Figure 2**. After magnetizing each sample up to 7 T with a pulse magnetizer, M-H loops were measured by using a vibrating sample magnetometer (VSM) which could apply a magnetic field up to approximately 1800 kA/m reversibly. The average thickness was mainly measured with a micrometer. In some samples, the thickness was estimated from hysteresis loops of as-deposited films [29]. Surface observation and composition analysis were carried out by using a scanning electron micro‐ scope (SEM) and an SEM-energy-dispersive X-ray spectroscopy (EDX), respectively.

[10]. Yamashita et al. also reported that the torque of a milli-size motor comprising a multipo‐ larlymagnetizedisotropicthickfilmexceededthetorqueofamotorusingananisotropicone[11]. In Sm-Co thick-film magnets, we have difficulty in overcoming the values of (*BH*)max for Nd-Fe-B films due to the low saturation magnetization. However, several researchers have demonstrated Sm-Co thick films because of their high Curie temperature and good corro‐ sion resistance [12–19]. For example, Cadieu et al. reported in-plane anisotropic Sm-Co films with a thickness above 100 μm using sputtering together with pulsed laser deposition (PLD) methods [16, 17]. In addition, Budde and Gatzen demonstrated a magnetic micro-actuator

Fe-Pt magnet is a promising material to use in the medical field owing to its outstanding biocompatibility [20]. In orderto advance medicalMEMS, the miniaturization of Fe-Pt magnets is necessary [21]. Aoyama and Honkura [22] and Liu et al. [23] reported isotropic Fe-Pt film magnets thicker than several microns using a sputtering method from the medical applica‐

Here, we show the properties of isotropic Nd-Fe-B [24–28] thick-film magnets prepared using the PLD method and several miniaturized machines [24, 25, 28] comprising the Nd-Fe-B thick film. Moreover, PLD-fabricated isotropic Sm-Co, Fe-Pt, and nano-composite Nd-Fe-B+α-Fe

A target such as Nd-Fe-B, Pr-Fe-B, Sm-Co, and Fe-Pt was ablated with an Nd-YAG pulse laser with a wavelength of 355 nm together with a frequency of 30 Hz in a vacuum atmosphere. The chamber was evacuated to approximately 4 × 10−5 Pa with a vacuum equipment before the deposition. During the deposition, each target was rotated and the distance between the target and the substrate (*T-S* distance) varied from 5 to 20 mm. In the experiment, a laser power was measured with a power meter in front of the entrance lens of the chamber. The laser energy density (LED) varied by controlling the laser power (LP) together with a spot size of laser beam which could be changed by moving the distance between the focal lens and the target intentionally (see **Figure 1**). Here, the spot size was expressed as a defocusing rate (DF rate) = (TD − FD)/FD × 100(%), where TD is the distance between the condensing lens and the target and FD is the focal length. In the experiment, the control of the defocusing rate (DF rate)

In some experiments, the post-annealing of a conventional annealing (CA) and a pulse annealing (PA), respectively, was carried out as shown in **Figure 2**. After magnetizing each sample up to 7 T with a pulse magnetizer, M-H loops were measured by using a vibrating sample magnetometer (VSM) which could apply a magnetic field up to approximately 1800 kA/m reversibly. The average thickness was mainly measured with a micrometer. In some samples, the thickness was estimated from hysteresis loops of as-deposited films [29]. Surface observation and composition analysis were carried out by using a scanning electron micro‐

scope (SEM) and an SEM-energy-dispersive X-ray spectroscopy (EDX), respectively.

enabled us to change LED widely compared with the variation of LP.

comprising a sputtering-made 30-μm-thick Sm-Co film [19].

tion point of view.

326 328High Energy and Short Pulse Lasers

**2. Experimental**

thick films were introduced.

**Figure 1.** Schematic diagrams of deposition process with several values of the laser energy density (LED) which was controlled by changing the laser power and DF rate independently. (a) High laser energy density (DF rate of zero: just focus) and (b) low laser energy density.

**Figure 2.** Schematic diagram of conventional annealing (CA) and pulse annealing (PA) methods.

### **3. Results**

#### **3.1. PLD-fabricated isotropic Nd-Fe-B thick-film magnets**

**Figure 3** shows the in-plane demagnetization curves of isotropic Nd-Fe-B thick-film mag‐ nets after the crystallization using two methods of CA and PA with each optimum condition. Both samples were prepared using an Nd2.4Fe14B target under the deposition rate higher than 40 μm/h. The annealing duration of PA was approximately 1.8 s and the ramping rate of CA was 400 K/min (see **Figure 2**). The coercivity value of the annealed film using PA meth‐ od was larger by approximately 300 kA/m than the annealed 673 K/min sample using CA method. On the other hand, the remanence and (*BH*)max values of the two samples were almost the same. Transmission electron microscopy (TEM) observation revealed that the use of PA method enabled us to reduce the size of Nd2Fe14B grains compared with that of the sample annealed using CA method. We considered that the enhancement in coercivity is due to the increases in the domain pinning sites. From these results, a high-speed crystallization annealing process (PA method) is a promising method to refine Nd2Fe14B grains of PLDfabricated Nd-Fe-B thick-film magnets.

**Figure 3.** Demagnetization curves (in-plane) of PLD-made Nd-Fe-B thick films crystallized by two methods of CA and PA.

**Figure 4** shows the relationship between the LED and magnetic properties of annealed Nd-Fe-B film magnets deposited on Ta substrates prepared using an Nd2.6Fe14B target. All the samples were annealed using PA method. As the inset in each figure shows, the laser power LP and DF rate were controlled independently. In low energy density, high coercivity (*Hc*) and low remanence (*Mr*) were obtained, respectively. The samples with low *Hc* and high *Mr* were prepared in high energy density. In order to obtain the high deposition rate above 40 μm/h, LED less than 30 mJ/mm2 was used. In this chapter, PA method was used in the results of

**3. Results**

328 330High Energy and Short Pulse Lasers

PA.

LED less than 30 mJ/mm2

**3.1. PLD-fabricated isotropic Nd-Fe-B thick-film magnets**

fabricated Nd-Fe-B thick-film magnets.

**Figure 3** shows the in-plane demagnetization curves of isotropic Nd-Fe-B thick-film mag‐ nets after the crystallization using two methods of CA and PA with each optimum condition. Both samples were prepared using an Nd2.4Fe14B target under the deposition rate higher than 40 μm/h. The annealing duration of PA was approximately 1.8 s and the ramping rate of CA was 400 K/min (see **Figure 2**). The coercivity value of the annealed film using PA meth‐ od was larger by approximately 300 kA/m than the annealed 673 K/min sample using CA method. On the other hand, the remanence and (*BH*)max values of the two samples were almost the same. Transmission electron microscopy (TEM) observation revealed that the use of PA method enabled us to reduce the size of Nd2Fe14B grains compared with that of the sample annealed using CA method. We considered that the enhancement in coercivity is due to the increases in the domain pinning sites. From these results, a high-speed crystallization annealing process (PA method) is a promising method to refine Nd2Fe14B grains of PLD-

**Figure 3.** Demagnetization curves (in-plane) of PLD-made Nd-Fe-B thick films crystallized by two methods of CA and

**Figure 4** shows the relationship between the LED and magnetic properties of annealed Nd-Fe-B film magnets deposited on Ta substrates prepared using an Nd2.6Fe14B target. All the samples were annealed using PA method. As the inset in each figure shows, the laser power LP and DF rate were controlled independently. In low energy density, high coercivity (*Hc*) and low remanence (*Mr*) were obtained, respectively. The samples with low *Hc* and high *Mr* were prepared in high energy density. In order to obtain the high deposition rate above 40 μm/h,

was used. In this chapter, PA method was used in the results of

**Figure 4.** Effects of energy density of laser beam on (a) coercivity and (b) remanence. The laser power LP and DF rate varied independently. (a) Coercivity and (b) Remanence.

#### **3.2. Applications comprising isotropic Nd-Fe-B thick-film magnets**

Several miniaturized devices comprising the above-mentioned isotropic Nd-Fe-B thick films were demonstrated [24, 25, 28]. **Figure 5(a)** shows a small DC brushless motor with a 200-μmthick isotropic PLD-made Nd-Fe-B film magnet. The values of coercivity and remanence of the film deposited on an Fe substrate were approximately 970 kA/m and 0.6 T, respectively. It was confirmed that the motor with a thickness of 0.8 mm and diameter of 5 mm rotates at approximately 15,000 rpm under no-load test. The torque constant of 0.0236 mNm/A showed at the gap of 0.1 mm between a rotor and a stator.

**Figure 5.** Three micro-machines comprising PLD-made Nd-Fe-B thick films. (a) DC brushless motor, (b) swimming machine in liquid, and (c) electromagnetic friction-drive micro-motor.

A spiral-type micro-machine with 0.14 mm in outer diameter and 1.0 mm in length was fabricated as seen in **Figure 5(b)**. In the machine, an isotropic PLD-made Nd-Fe-B film magnet was deposited on a tungsten (W) wire. After magnetizing the film magnet in the circumfer‐ ential direction, the machine rotated in sync with the rotating external magnetic field and the spiral structure generated the propellant force. In the experiment, three types of liquids with kinematic viscosity of 1, 10, and 100 mm2 /s, respectively, were used. In order to move the wireless micro-machine, an external magnetic field of 8 kA/m was applied under the frequen‐ cy range between 2 and 10 Hz. It was confirmed that the machine swam at the speed of 0.2– 1.6 mm/s under various conditions.

A micro-motor using a PLD-made Nd-Fe-B film magnet with a thickness of 384 μm deposit‐ ed on a Ta substrate was demonstrated as shown in **Figure 5(c)**. The statoris a coil with a ferrite core in the center together with a ferrite disc at the bottom. As an alternating voltage was applied to the coil, pulling and reacting forces worked alternatively between the film and the ferrite core, and as a result the rotor of the film magnet vibrated. The rotor is magnetically mounted onto the stator without mechanical attachments. The motor rotated at approximate‐ ly 300 rpm with a starting torque of approximately 2 μNm. We confirmed that the electro‐ magnetic friction-drive motor had a large torque together with a low rotational speed.

#### **3.3. Isotropic Nd-Fe-B thick-film magnets deposited on Si substrates**

was confirmed that the motor with a thickness of 0.8 mm and diameter of 5 mm rotates at approximately 15,000 rpm under no-load test. The torque constant of 0.0236 mNm/A showed

**Figure 5.** Three micro-machines comprising PLD-made Nd-Fe-B thick films. (a) DC brushless motor, (b) swimming

A spiral-type micro-machine with 0.14 mm in outer diameter and 1.0 mm in length was fabricated as seen in **Figure 5(b)**. In the machine, an isotropic PLD-made Nd-Fe-B film magnet was deposited on a tungsten (W) wire. After magnetizing the film magnet in the circumfer‐ ential direction, the machine rotated in sync with the rotating external magnetic field and the

machine in liquid, and (c) electromagnetic friction-drive micro-motor.

at the gap of 0.1 mm between a rotor and a stator.

330 332High Energy and Short Pulse Lasers

As mentioned earlier, increase in thickness of an Nd-Fe-B film magnet is indispensable to provide a sufficient magnetic field. Here, the deposition ofisotropic Nd-Fe-B thick-film magnet on Si substrates was carried out in order to apply the film magnet to various MEMS. It is generally known that we had difficulty in suppressing the peeling phenomenon due to the different values of a linear expansion coefficient for a Si substrate and an Nd-Fe-B film. Even if a buffer layer such as a Ta film was used, the maximum thickness was less than 200 μm. Here, we reported that a control of microstructure of Nd-Fe-B thick films enabled us to increase the thickness above 100 μm without a buffer layer on Si substrates [30].

**Figure 6.** Relationship between thickness and Nd contents in isotropic Nd-Fe-B thick-film magnets deposited on Si substrates after an annealing process. Increase in Nd contents enabled us to increase the thickness up to 160 μm with‐ out mechanical destruction.

We investigated the relationship between thickness and Nd contents in annealed isotropic Nd-Fe-B thick films deposited on SiO2/Si substrates as seen in **Figure 6**. After all the samples were

annealed using PA method, many samples displayed by the symbol "○" could be prepared without mechanical destruction. All the other samples plotted as "●" were broken. As the Nd content exceeded by approximately 22 at.%, the thickness of the sample symbolized "○" could be enhanced up to approximately 160 μm. The thickness of Nd-Fe-B films deposited on Si substrates increased without the deterioration of mechanical properties. It was considered that the precipitation of Nd element at the boundary of Nd-Fe-B grains together with the triple junctions due to the composition adjustment of Nd2Fe14B phase is effective to suppress the destruction of the samples through an annealing process.

#### **3.4. Isotropic Pr-Fe-B thick-film magnets deposited on glass substrates**

The laser beam was focused on the surface of a PrXFe14B (X = 1.8–2.4) target under a high deposition rate of approximately several tens of microns per hour (see **Figure 1(b)**). **Figure 7** shows the magnetic properties as a function of Pr contents in each film with a thickness above 10 μm. Coercivity increased and residual magnetic polarization decreased with an increase in the amount of Pr. As displayed in **Figure 6**, Nd(or Pr)-Fe-B thick films with rareearth amount less than 15 at.% deposited on Si substrates were mechanically broken after a post-annealing process. On glass substrates, the Pr amounts could be reduced down to approximately 13 at.% without the deterioration of mechanical properties. It was also confirmed that an approximately 100-μm-thick Pr-Fe-B thick film with (*BH*)max of about 80 kJ/ m3 could be deposited on a glass substrate.

**Figure 7.** Remanence and coercivity as a function of Pr contents in Pr-Fe-B thick-film magnets deposited on glass sub‐ strates.

#### **3.5. PLD-fabricated isotropic Sm-Co thick-film magnets**

In this section, a high-speed PLD method with a deposition rate of approximately several tens of microns per hour was applied to fabricate Sm-Co thick-film magnets by using an Sm1.2Co5 target. In-plane and perpendicular M-H loops of a sample annealed by CA method are shown

in **Figure 8**. The perpendicular M-H loop was corrected by a demagnetization factor of 1.0. The structure of as-deposited films prepared using an SmCo5 target without a substrate heating system was amorphous as seen in **Figure 9**; therefore, the samples were post-annealed at a temperature of 973 K with a heating rate of 673 K/min (CA method). After the post anneal‐ ing, not only SmCo5 but also Sm2Co17 phases were observed. In the present stage, we demon‐ strate the fabrication nano-composite Sm-Co/α-Fe multilayered film magnets using the PLD method [31].

annealed using PA method, many samples displayed by the symbol "○" could be prepared without mechanical destruction. All the other samples plotted as "●" were broken. As the Nd content exceeded by approximately 22 at.%, the thickness of the sample symbolized "○" could be enhanced up to approximately 160 μm. The thickness of Nd-Fe-B films deposited on Si substrates increased without the deterioration of mechanical properties. It was considered that the precipitation of Nd element at the boundary of Nd-Fe-B grains together with the triple junctions due to the composition adjustment of Nd2Fe14B phase is effective to suppress the

The laser beam was focused on the surface of a PrXFe14B (X = 1.8–2.4) target under a high deposition rate of approximately several tens of microns per hour (see **Figure 1(b)**). **Figure 7** shows the magnetic properties as a function of Pr contents in each film with a thickness above 10 μm. Coercivity increased and residual magnetic polarization decreased with an increase in the amount of Pr. As displayed in **Figure 6**, Nd(or Pr)-Fe-B thick films with rareearth amount less than 15 at.% deposited on Si substrates were mechanically broken after a post-annealing process. On glass substrates, the Pr amounts could be reduced down to approximately 13 at.% without the deterioration of mechanical properties. It was also confirmed that an approximately 100-μm-thick Pr-Fe-B thick film with (*BH*)max of about 80 kJ/

**Figure 7.** Remanence and coercivity as a function of Pr contents in Pr-Fe-B thick-film magnets deposited on glass sub‐

In this section, a high-speed PLD method with a deposition rate of approximately several tens of microns per hour was applied to fabricate Sm-Co thick-film magnets by using an Sm1.2Co5 target. In-plane and perpendicular M-H loops of a sample annealed by CA method are shown

destruction of the samples through an annealing process.

332 334High Energy and Short Pulse Lasers

could be deposited on a glass substrate.

**3.5. PLD-fabricated isotropic Sm-Co thick-film magnets**

m3

strates.

**3.4. Isotropic Pr-Fe-B thick-film magnets deposited on glass substrates**

**Figure 8.** In-plane and perpendicular M-H loops of a PLD-fabricated Sm-Co thick film after a post-annealing process.

**Figure 9.** X-ray diffraction patterns of a PLD-fabricated Sm-Co thick film before and after a post-annealing process.

#### **3.6. PLD-fabricated isotropic Fe-Pt thick-film magnets**

In this section, a Fe70Pt30 target was ablated with an Nd-YAG pulse laser under LED above 200 mJ/mm2 in a vacuum atmosphere (see **Figure 1(a)**). **Figure 10** shows coercivity values of the as-deposited films as a function of laser power. The values drastically increased at a power of 3 W and then gradually decreased with increase in power. We confirmed that the sub‐ strate temperature was proportional to the laser power due to the rise of a radiation heat from a target. As a result, it was found that L10 ordered phase together with relatively high coercivity could be obtained using a suitable laser power without using a substrate heating system and a post-annealing process. **Figure 11** shows in-plane M-H loop of a Fe-Pt film fabricated at a power of 3 W. The values of coercivity, remanence, and (*BH*)max were 378 kA/m, 0.94 T, and 104 kJ/m3 , respectively [32]. We, therefore, considered that remanence enhancement occur‐ red in the sample because the saturation magnetization of 1.43 T for Fe50Pt50 ordered phase [33].

**Figure 10.** In-plane coercivity values for as-deposited Fe-Pt film magnets prepared from Fe70Pt30 target as a function of laser power.

**Figure 11.** In-plane and perpendicular M-H loops of an as-deposited Fe-Pt film magnet prepared from a Fe70Pt30 target.

#### **3.7. PLD-fabricated isotropic nano-composite Nd-Fe-B + α-Fe thick-film magnets**

**3.6. PLD-fabricated isotropic Fe-Pt thick-film magnets**

200 mJ/mm2

334 336High Energy and Short Pulse Lasers

104 kJ/m3

laser power.

In this section, a Fe70Pt30 target was ablated with an Nd-YAG pulse laser under LED above

the as-deposited films as a function of laser power. The values drastically increased at a power of 3 W and then gradually decreased with increase in power. We confirmed that the sub‐ strate temperature was proportional to the laser power due to the rise of a radiation heat from a target. As a result, it was found that L10 ordered phase together with relatively high coercivity could be obtained using a suitable laser power without using a substrate heating system and a post-annealing process. **Figure 11** shows in-plane M-H loop of a Fe-Pt film fabricated at a power of 3 W. The values of coercivity, remanence, and (*BH*)max were 378 kA/m, 0.94 T, and

red in the sample because the saturation magnetization of 1.43 T for Fe50Pt50 ordered phase [33].

**Figure 10.** In-plane coercivity values for as-deposited Fe-Pt film magnets prepared from Fe70Pt30 target as a function of

**Figure 11.** In-plane and perpendicular M-H loops of an as-deposited Fe-Pt film magnet prepared from a Fe70Pt30 target.

in a vacuum atmosphere (see **Figure 1(a)**). **Figure 10** shows coercivity values of

, respectively [32]. We, therefore, considered that remanence enhancement occur‐

In this section, we focus on the use of high LED above 200 mJ/mm2 in order to adopt a different deposition process by taking account of the explosively emitting process of atoms from a target. The as-deposited films had amorphous phase including α-Fe grains, and a nano-composite structure could be obtained after the pulse annealing [34].

**Figure 12.** Relationship between remanence and coercivity values of films thicker than 10 μm by using six targets with various compositions. Use of an Nd2.4Fe14B target is effective to obtain good magnetic properties.

**Figure 13.** M-H loop of a 16-μm-thick Nd-Fe-B film magnet prepared using laser energy density above 200 mJ/mm2 together with an Nd2.4Fe14B target.

Investigation on the relationship between coercivity and remanence of each sample thicker than 10 μm prepared by six Nd-Fe-B targets with various compositions under LED above 200 mJ/mm2 (see **Figure 12**). In all the targets, the deposition rate was higher than 20 μm/h and the reduction in the Nd contents of each film by several atomic percentages was observed compared with that of the corresponding target. The samples prepared by using an Nd2.4Fe14B target had relatively large values of coercivity and remanence. **Figure 13** shows an in-plane M-H loop of a 16-μm-thick Nd-Fe-B + α-Fe thick-film magnet prepared using LED higher than 200 mJ/mm2 together with an Nd2.4Fe14B target.
