High Saturation Magnetostriction Research Articles

Optimizing laser additive manufacturing process for Fe-based nano-crystalline magnetic materials

Fe-based amorphous magnetic alloys offer new opportunities for magnetic sensors, actuators and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20–40 ppm) compared with that of amorphous Co-based alloys (λs = −3 to −5 ppm). Due to the conventional production limitations of Fe-based glassy alloys, including dimensional limitations and poor mechanical properties, this has led to a search for novel fabrication techniques. Recently, the laser powder bed fusion (LPBF) technique has attracted attention for the production of Fe-based magnetic bulk metallic glasses (BMGs) as it provides high densification, which brings about excellent mechanical properties, and high cooling rate during the process. Optimization of process parameters in the LPBF technique have been studied using the volumetric energy input (E), which includes the major build parameters; laser power (P), scan speed (v), layer thickness (t) and hatch spacing (h). This study investigates how the major process parameters influence the physical and magnetic properties of LPBF-processed Fe-based amorphous/nanocrystalline composites ((Fe87.38Si6.85B2.54Cr2.46C0.77 (mass %)). Various process parameter combinations with P (90, 100, 120 and 150 W) and v (700, 1000 and 1300 mm/s) were applied with t of 30, 50 and 70 µm and h of 20, 30, 40, 50 and 60 µm. It was found that bulk density improves as P and t increases, v and h decreases, i.e., high E is necessary, however, 99.45% of bulk density was achieved with E of 61.22 J/mm3 (P = 150 W, v=700 mm/s, h=50 µm and t = 70 µm), which indicates the importance of understanding how parameters affect the specific materials. In addition, the magnetic properties differ significantly due to the nanocrystalline phases present in the microstructure, with their size depending on the process parameters considerably. Owing to the laser scanning nature, the microstructure evolves as molten pools (MP) and heat affected zones (HAZ) due to the high thermal gradient that occurred between laser tracks. MP form around the scans, containing α-Fe(Si) nanograins mainly, whereas HAZ generally contains Fe2B and Fe3Si nanocrystalline clusters. The size and quantities of those nanocrystallites determine the magnetic properties. With the same E (60 J/mm3), v (1000 mm/s) and t (50 µm), only changing P and h caused samples to have different saturation magnetization; 206 emu/gr (P: 90 W and h: 30 µm) and 150 emu/gr (P: 150 W and h: 50 µm). In general, the saturation magnetisation, Ms of LPBF-processed samples changes between 130 and 206 emu/gr, which is much higher than that of feedstock powder (102 emu/gr) due to their nanocrystalline structures. The coercivity (Hc) is in the range of 14.55 and 34.68 Oe, which is considered high for soft-magnetic behaviour (Hc ≤ 12.5 Oe), resulting from the larger crystallite size and the presence of defects (pores and cracks) in the microstructure.

Unconventional metamagnetic phase transition in R2In (R=Nd, Pr) with lambda-like specific heat and nonhysteresis

• The field-triggered metamagnetism with lambda-like peak on the specific heat is found in Nd 2 In and Pr 2 In alloys. • Neither thermomagnetic hysteresis nor lattice changes are observable during phase transition. • Giant magnetoentropy changes of 13.2 J kg −1 K −1 and 19.5 J kg −1 K −1 are achieved with enhanced magnetoelastic coupling. • The max adiabatic temperature changes of 6.5 K and 7.4 K are obtained for Nd 2 In and Pr 2 In alloys under 7 T. • It is proposed to be from the delocalized 5 d electrons evidenced by the negative magnetoresistance. The phase transition of Nd 2 In and Pr 2 In has been studied and found to be between the first-order and second-order nature. Hardly any hysteresis nor obvious cell volume changes are presented. Concurrently the field-triggered metamagnetism is demonstrated with lambda-like peak on specific heat curve. For the field change of 7 T, giant magnetic entropy changes of 13.2 J kg −1 K −1 and 19.5 J kg −1 K −1 and adiabatic temperature changes of 6.5 K and 7.4 K have been achieved in Nd 2 In and Pr 2 In alloys respectively, which is partially contributed by strong magnetoelastic coupling represented by high saturation magnetostriction of ∼450 ppm. Such unique feature is proposed to be originated from the delocalized 5 d electrons, as evidenced by the negative magnetoresistance caused by the phase transition.

Laser Additive Manufacturing of Fe-Based Magnetic Amorphous Alloys

Fe-based amorphous materials offer new opportunities for magnetic sensors, actuators, and magnetostrictive transducers due to their high saturation magnetostriction (λs = 20–40 ppm) and low coercive field compared with polycrystalline Fe-based alloys, which have high magnetostriction but large coercive fields and Co-based amorphous alloys with small magnetostriction (λs = −3 to −5 ppm). Additive layer manufacturing (ALM) offers a new fabrication technique for more complex net-shaping designs. This paper reviews the two different ALM techniques that have been used to fabricate Fe-based amorphous magnetic materials, including the structural and magnetic properties. Selective laser melting (SLM)—a powder-bed fusion technique—and laser-engineered net shaping (LENS)—a directed energy deposition method—have both been utilised to fabricate amorphous alloys, owing to their high availability and low cost within the literature. Two different scanning strategies have been introduced by using the SLM technique. The first strategy is a double-scanning strategy, which gives rise to maximum relative density of 96% and corresponding magnetic saturation of 1.22 T. It also improved the glassy phase content by an order of magnitude of 47%, as well as improving magnetic properties (decreasing coercivity to 1591.5 A/m and increasing magnetic permeability to around 100 at 100 Hz). The second is a novel scanning strategy, which involves two-step melting: preliminary laser melting and short pulse amorphisation. This increased the amorphous phase fraction to a value of up to 89.6%, and relative density up to 94.1%, and lowered coercivity to 238 A/m. On the other hand, the LENS technique has not been utilised as much as SLM in the production of amorphous alloys owing to its lower geometric accuracy (0.25 mm) and lower surface quality, despite its benefits such as providing superior mechanical properties, controlled composition and microstructure. As a result, it has been commonly used for large parts with low complexity and for repairing them, limiting the production of amorphous alloys because of the size limitation. This paper provides a comprehensive review of these techniques for Fe-based amorphous magnetic materials.

Enhancing the soft magnetic properties of FeGa with a non-magnetic underlayer for microwave applications

An ultra-thin (∼2.5 nm) non-magnetic Cu underlayer was found to have a significant effect on the microstructure, magnetic softness, and magnetostriction of sputter-deposited Fe81Ga19 (FeGa) thin films. Compared to the experimental control where FeGa was deposited directly on Si without an underlayer, the presence of Cu increased the in-plane uniaxial anisotropy of FeGa and reduced the in-plane coercivity by nearly a factor of five. The effective Gilbert damping coefficient was also significantly reduced by a factor of four, between FeGa on Si and FeGa on a Cu underlayer. The FeGa films on Cu also retained a high saturation magnetostriction comparable to those without an underlayer. The enhancement of the desirable magnetic properties for microwave applications is attributed to the Cu underlayer, promoting the (110) film texture and increasing the compressive film strain. The results demonstrated that the structural control is viable to simultaneously achieve the necessary magnetic softness and magnetostriction in FeGa for integration in strain-mediated magnetoelectric and microwave devices.

Soft Magnetism, Magnetostriction, and Microwave Properties of Fe-Ga-C Alloy Films

A systematic investigation of the soft magnetism, the change of modulus of elasticity with magnetization (ΔE effect), magnetostriction, and microwave properties has been carried out on iron-gallium-carbon thin films over a wide carbon content range. The phase transformation of the Fe-Ga-C films from bcc polycrystalline to amorphous leads to excellent magnetic softness with a low coercivity of less than 1 Oe, high saturation magnetization, narrow ferromagnetic resonance linewidth at 10 GHz of 20 to 30 Oe, and an ultra-low Gilbert damping constant of 0.0027. A record high piezomagnetic coefficient of 9.71 ppm/Oe, high saturation magnetostriction constant of 81.2 ppm, and large ΔE effect of -120 GPa at 500 nm were achieved.

Tuning static and dynamic properties of FeGa/NiFe heterostructures

In this work, the frequency-dependent magnetic properties of sputtered Galfenol/Permalloy (Fe85Ga15/Ni81Fe19 or FeGa/NiFe) magnetic multilayers were examined to tailor their magnetic softness, loss at microwave frequencies, permeability, and magnetoelasticity, leveraging the magnetic softness and low loss of NiFe and the high saturation magnetostriction (λs) and magnetization (MS) of FeGa. The total volume of each material and their ratio were kept constant, and the number of alternating layers was increased (with decreasing individual layer thickness) to assess the role of increasing interfaces in these magnetic heterostructures. A systematic change was observed as the number of bilayers or interfaces increases: a seven-bilayer structure results in an 88% reduction in coercivity and a 55% reduction in ferromagnetic resonance linewidth at the X-band compared to a single phase FeGa film, while maintaining a high relative permeability of 700. The magnetostriction was slightly reduced by the addition of NiFe but was still maintained at up to 67% that of single phase FeGa. The tunability of these magnetic heterostructures makes them excellent candidates for RF magnetic applications requiring strong magnetoelastic coupling and low loss.

急冷CoFe合金薄帯の磁気・磁歪特性に及ぼす熱処理・圧延効果

Co-rich Co-Fe alloy is known to possess of high saturation magnetostriction, high Curie temperature and good mechanical property. In this study, the rapidly solidified Co75Fe25 alloy were studied for appearance further large magnetostriction due to change in both of the structure and the texture by a combination of heat treatment and cold-rolling. The Co-Fe alloy ribbons were produced by a single Cu-roller rapid solidification, and subsequently annealed at 973-1023K for 1h in vacuum atmosphere after rolling. For evaluation of the heat treatment effect and the rolling effect, magnetic properties such as magnetization, coercivity, magnetostriction and susceptibility were measured as well as crystal structure. As a result, enhancement of magnetostriction improved due to combination of cold-rolling and annealing because precipitating appearance of fcc phase decreased, and also magnetostrictive susceptibility improved caused by enhancement of magnetostriction reached to about 2 times. Additionally the coercivity of annealed specimens after rolling showed a decreasing tendency compared with that of without rolling.

Optimization on magnetic anisotropy and magnetostriction in TbxHo0.8−xPr0.2(Fe0.8Co0.2)1.93 compounds

The structure, magnetocrystalline anisotropy compensation, magnetic properties, and magnetostriction of TbxHo0.8–xPr0.2(Fe0.8Co0.2)1.93 (0≤x≤0.30) polycrystalline alloys have been investigated. X-ray diffraction (XRD) analysis shows that all the alloys stabilize in the single Laves phase with a MgCu2-type cubic structure. The lattice parameter, Curie temperature and saturation magnetization monotonically increase with increasing Tb content. The easy magnetization direction (EMD) at room temperature is detected rotating from the <100> axis (x≤0.10) to the <111> axis (x≥0.15), accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111. The analysis of XRD, EMD and magnetostriction shows that TbxHo0.8–xPr0.2(Fe0.8Co0.2)1.93 is an anisotropy compensation system, and the critical compensation point is realized around x=0.15, which shifts to the Tb-poor side compared with the Pr-free counterpart. An optimized effect on magnetostriction especially at a relatively low field (λS~445ppm, λa~510ppm/3kOe) was obtained in Tb0.15Ho0.65Pr0.2(Fe0.8Co0.2)1.93 compound, which is much larger than that of the Pr-free counterpart Tb0.15Ho0.85(Fe0.8Co0.2)1.93 (λS~300ppm) and the Tb0.15Ho0.85Fe2 (λS~325ppm), due to the 20at% Pr introduction. Low content of heavy rare earth Tb, low anisotropy, high saturation magnetostriction and large low-field magnetostriction are obtained in Tb0.15Ho0.65Pr0.2(Fe0.8Co0.2)1.93 compound, which may make it a promising magnetostrictive material.

Magnetoelastic properties of Co-doped Laves compounds TbxHo0.9−xNd0.1Fe1.93 (0≤x≤0.40)

Structure, spin configuration, magnetocrystalline-anisotropy compensation, magnetization, and magnetostriction of TbxHo0.9-xNd0.1(Fe0.8Co0.2)(1.93) (0 axis when x >= 0.25, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients lambda(111). The anisotropy compensation can be achieved by evaluating EMD, magnetization and magnetostriction, and the critical point is realized to be around x = 0.25. The good magnetoelastic properties, e.g., the low anisotropy at room temperature, high polycrystalline saturation magnetostriction (lambda(s) similar to 560 ppm) and large spontaneous magnetostriction coefficient (lambda(111) similar to 850 ppm), are achieved for the Tb0.25Ho0.65Nd0.1 (Fe0.8Co0.2)(1.93) compound, which may make it a promising magnetostrictive material. (C) 2015 Elsevier Ltd. All rights reserved.

Microstructures and Magnetic Properties of Fe70−x Pd30Ni x High-Temperature Ferromagnetic Shape Memory Alloys

This research paper mainly presents an investigation of the microstructures and magnetic properties of bulk ferromagnetic shape memory (FSM) Fe70−x Pd30Ni x (Ni x = 4, 8 at.%) alloys, by transmission electron microscopy (TEM), a magnetostrictive-meter setup, and a superconducting quantum interference device (SQUID) magnetometer. The FSM alloys were homogenized through hot and cold strain forging (SF) to a ∼38 % reduction in thickness, solution-treated (ST) with annealing recrystallization at 1100 °C or 8 h, quenched in ice brine, and then aged at 500 °C for 100 h (5 HTA). The investigation of the microstructures and magnetic properties indicated that the higher Ni content (N x = 8 at.%) in the Fe62Pd30Ni8 alloy SF and ST reduced the saturation magnetostriction at RT. However, with higher Ni content in the Fe62Pd30Ni8 alloy, the decomposition of L10 + L1m twin phases into stoichiometric L10 + L1m + α bct structures was suppressed after the alloy was ST and aged at 5 HTA, as confirmed by TEM investigation. The result was that the FSM Fe62Pd30Ni8 alloy maintained a high saturation magnetostriction and magnetization after the alloy was ST and aged at 5 HTA. This magnetic property of the Fe62Pd30Ni8 FSM alloy makes it suitable for application in high-temperature (T < 500 °C) and high-frequency environments. However, low Ni content FSM Fe66Pd30Ni4 (N x = 4 at.%) alloy SF, ST, and aged at 5 HTA underwent decomposition of the L10 + L1m twin phases into the stoichiometric L10 + L1m + α bct structures, as confirmed by TEM, leading to a decrease of saturation magnetostriction and magnetization. This magnetic property of the Fe66Pd30Ni4 FSM alloy is not suitable for application in high-temperature (T < 500 °C) environments.

An investigation of the effect of structural order on magnetostriction and magnetic behavior of Fe–Ga alloy thin films

This paper reports results from a comprehensive study of Fe–Ga films fabricated over a wide range of growth conditions. Polycrystalline Fe 100− x Ga x films (14 ⩽ x ⩽ 32) were deposited (using three different combinations of growth parameters) on Si(1 0 0) using a co-sputtering and evaporation technique. The growth parameters (sputter power, Ga evaporation rate and chamber pressure) were used primarily to control the Fe:Ga ratio in the films. X-ray diffraction showed that all films had 〈1 1 0〉 crystallographic texture normal to the film plane. The lattice parameter increased with % Ga up to x = 22 and was independent of growth parameters. Conversion electron Mössbauer spectroscopy studies showed a predominance of the disordered A2 phase in all films. It appears that the use of vacuum deposition with appropriate parameters can effectively suppress the D0 3 ordered phase. Systematic studies of the effective magnetostriction constant as a function of composition support this conclusion. It was found that films of high effective saturation magnetostriction constant and low stress could be fabricated using low Ar pressure, irrespective of sputter power or evaporation rate, giving properties useful for application in microelectromechanical systems.

Amorphous Terfenol-D films using nanosecond pulsed laser deposition

Thin films of Terfenol-D were produced by nanosecond pulsed laser deposition (PLD) at two fluences. Electron dispersive spectroscopy conducted using scanning electron and transmission electron microscopes showed that the film compositions were similar to that of the PLD target. Contrary to previous assertions that suggested that nanosecond PLD results in crystalline films, X-ray diffraction and transmission electron microscopy analysis showed that the films produced at both fluences were amorphous. Splatters present on the film had similar compositions to the overall film and were also amorphous. Magnetic measurements showed that the films had high saturation magnetization and magnetostriction, similar to high quality films produced using other physical vapor deposition methods.

Structure and magnetic properties of magnetostrictive rapidly-quenched alloys for force sensors applications

This work was aimed at investigating the FeNiMoB type alloys exhibiting relatively high saturation magnetostriction after suitable heat treatment, which makes them suitable for application in force sensors. Crystallization process of amorphous alloy was examined by DSC. Temperatures and enthalpies of both stages of crystallization were determined from DSC upon continuous heating from a room temperature to 993 K with constant heating rate of 20 K/min. Next, samples were isothermally annealed under longitudinal and transverse magnetic fields within the temperature range of 623–833 K for 1 h under Ar protective atmosphere. Structure of the alloys was checked by means of XRD and TEM. After annealing, the AC (50 Hz) magnetic properties (coercivity, magnetic induction) were determined using a computerized hysteresis loop tracer. An effect of the annealing temperature, induced magnetic anisotropy and of the applied compressive stresses on the dynamic magnetic properties of the alloys was studied within a frequency range from 50 Hz to 50 kHz. Our studies confirmed that the Fe-Ni-Mo-B alloy annealed at 653 K is the most suitable for application in force sensors. Moreover, the results obtained indicate that for the measurements of compressive stresses below 0.3 MPa it is more advantageous to use the cores with longitudinal anisotropy, whereas the cores with a transverse magnetic anisotropy are more suitable for application at the compressive stresses over 0.3 MPa.

Strong magnetoelectric coupling at microwave frequencies in metallic magnetic film/lead zirconate titanate multiferroic composites

Strong magnetoelectric coupling was observed at microwave frequencies in metallic magnetic film/lead zirconate titanate [Pb(Zr,Ti)O3] multiferroic composites, in which the magnetic films were either FeCoB or FeGaB with relatively high saturation magnetostriction constants between 40 and 70ppm and narrow ferromagnetic resonance linewidths of ∼20Oe at 10GHz. Large electrostatically induced ferromagnetic resonance frequency shifts of 50–110MHz at ∼2.3GHz were observed. These metallic magnetic film/Pb(Zr,Ti)O3 multiferroic composites with large electrostatic tunability of the ferromagnetic resonance frequency provide great opportunities for integrated microwave multiferroic devices.

Dynamic Magnetic Properties of the Magnetostrictive Rapidly-Quenched Alloys

This work was aimed at investigating the FeNbCuSiB and FeNiMoB type alloys exhibiting relatively high saturation magnetostriction after suitable heat treatment, which makes them suitable for application in force sensors. Samples of both alloys were prepared in a form of toroidal cores wound from amorphous ribbons obtained by melt-spinning, and then the cores were annealed under longitudinal and transverse magnetic field. An effect of the induced magnetic anisotropy and of the applied compressive stresses on the dynamic magnetic properties of both alloys within a frequency range from 50 Hz to 50 kHz was studied.

Soft magnetism, magnetostriction, and microwave properties of FeGaB thin films

A series of (Fe100−yGay)1−xBx (x=0–21 and y=9–17) films were deposited; their microstructure, soft magnetism, magnetostrictive behavior, and microwave properties were investigated. The addition of B changes the FeGaB films from polycrystalline to amorphous phase and leads to excellent magnetic softness with coercivity &amp;lt;1Oe, high 4πMs, self-biased ferromagnetic resonance (FMR) frequency of 1.85GHz, narrow FMR linewidth (X band) of 16–20Oe, and a high saturation magnetostriction constant of 70ppm. The combination of these properties makes the FeGaB films potential candidates for tunable magnetoelectric microwave devices and other rf/microwave magnetic device applications.

Effect of grain shape on magnetostrictive polycrystalline Fe–Ga alloys

Polycristalline Fe 100− x Ga x alloys with 15 < x < 30 present high saturation magnetostriction, which depends strongly on the preparation method. We found that the longitudinal magnetostrictions of copper mold-cast polycrystalline Fe 80Ga 20 and Fe 71Ga 29 alloys are three times larger along the axis parallel to the temperature gradient, than those along the axis perpendicularly to the TG. For x = 0 and 29 the magnetostriction increases with decreasing temperature, reaching a value of 150 ppm at 4.2 K in the Fe 71Ga 29 alloy. However for x = 20 a different behavior was found. These results are related to the particular microstructure composed of large and elongated grains and with crystallographic texture.

ＦｅＣｏＳｉＢアモルファス薄膜を用いた高感度歪センサ

Amorphous FeCoSiB films with high saturation magnetostriction and excellent soft magnetic properties were studied to determine their strain sensitivity. The films were subjected to strain by bending of their substrates, which caused a change in the magnetic anisotropy of films via magnetoelastic coupling. The films exhibited a figure of merit F ≡ (θμ/θε)/μ (change in film permeability μ per unit of strain ε) of 1.2 × 105, which is comparable to that of amorphous ribbons. To study the use of the magnetostrictive films as strain sensor elements, we prepared meander-patterned films by means of the photolithography and ion milling processes. The impedance change in the patterned films when strain was applied was measured in the frequency range from 1 MHz to 1 GHz. Reflecting the large value of F, the high-frequency impedance of the films was changed considerably: a change in impedance of 46% was observed at 100 MHz when a strain of 300 × 10-6 was applied. It is also demonstrated that, by using the strain-dependent impedance, a small strain of 1 × 10-7 can be detected by means of the film pattern.

Interface Governed Magnetostriction in Ultra Thin CoFe and Fe Films

ABSTRACTTwo different types of polycrystalline films, films with low (Fe) and films with high (Co50Fe50) saturation magnetostriction λs, were sandwiched between Cu to study the thickness dependence of λs in Cu/X/Cu systems. We utilised a new method (ROTMOKE) for a high accurate Hk determination. The values for X, were determined by analysing the change of Hk during application of compressive and tensile stress by cylindrical bending of the substrate joint with the film. For both systems, a remarkable contribution of the interface to the λs, was found. The sign of the interface contribution is opposed to the sign of bulk λs, leading to a zero transition of λs., For Fe this transition occurs at a thickness of 5 nm whereas for the CoFe film with a strong λs, value of the bulk of around 80 · 10−6 a transition was extrapolated at a thickness around 1 nm.

Striped domain of Fe-based amorphous ribbon under various Lorentz SEM conditions

Magnetic domains of field annealed Fe 80.5 Si 7 B 12 C 0.5 amorphous ribbon were investigated by observation with Lorentz SEM, varying accelerating voltage and beam scanning area using backscattered electron distribution, so-called Type-2 contrast. A typical striped pattern, with Landau-Lifshitz type domain superimposed on main 180 degree domains, was obtained under the condition of high accelerating voltage and large aperture. It is attributed to the thermal strain under these observation conditions. The possibility to create another type of stressed domain pattern during the observation in SEM is discussed in rapidly quenched Fe-based amorphous ribbons due to high saturation magnetostriction and low thermal conductivity.