Vladimir Keylin

Composition dependence of field induced anisotropy in ferromagnetic (Co,Fe)89Zr7B4 and (Co,Fe)88Zr7B4Cu1 amorphous and nanocrystalline ribbons

The composition dependence of field induced anisotropy KU of field annealed soft ferromagnetic (Co1−xFex)89Zr7B4 and (Co1−xFex)88Zr7B4Cu1 amorphous and amorphous/nanocrystalline “nanocomposite” melt spun ribbons is investigated. With the exception of the highest Co-containing alloys (x<∼0.10), the observations are discussed in terms of a superposition of directional pair ordering of Fe,Co atoms and an additional contribution presumably due to the presence of Zr and B in both the field crystallized and field annealed amorphous ribbons. The highest Co-containing alloys (x<∼0.10) contain multiple nanocrystalline phases (bcc, fcc, and hcp) for which a peak in KU is observed (KU∼2000–2500 J/m3). In this framework, asymmetry in the compositional dependence of KU resulting in larger values for Co-rich alloys relative to Fe-rich alloys for both the field crystallized and field annealed amorphous alloys is explained in terms of a strong dependence of the Curie temperature of the amorphous phase on the Co content.

Nanocrystalline material development for high-power inductors

A new high-saturation induction, high-temperature nanocomposite alloy for high-power inductors is discussed. This material has FeCo with an A2 or B2 structure embedded in an amorphous matrix. An alloy of composition Fe56Co24Nb4B13Si2Cu1 was cast into a 1.10in. wide, 0.001in. thick ribbon from which a toroidal core of approximately 4.25in. outer diameter, 1.38in. inner diameter, and 1.10in. tall was wound. The core was given a 2T transverse magnetic field anneal, and impregnated for strength. Field annealing resulted in a linear B-H response with a relative permeability of 1400 that remained constant up to field strengths of 1.2T. The core was used to construct a 25μH inductor for a 25kW dc-dc converter. The inductor was rated for operation in discontinuous conduction mode at a peak current of 300A and a switching frequency of up to 20kHz. Compared to commercially available materials, this new alloy can operate at higher flux densities and higher temperatures, thus reducing the overall size of the inductor.

Temperature stability of field induced anisotropy in soft ferromagnetic Fe,Co-based amorphous and nanocomposite ribbons

The temperature stability of field induced uniaxial anisotropy (KU) was investigated by thermomagnetic treatments of (Co1−xFex)89Zr7B4 amorphous ribbons after field annealing below and above the crystallization temperature. We conclude: (1) Field annealing treatments are necessary to properly investigate the temperature stability of KU, (2) KU of field crystallized alloys exhibit improved temperature stability relative to alloys remaining amorphous after field annealing, and (3) larger KU is obtained for field crystallization treatments as compared to zero-field crystallization followed by field reannealing. Field crystallization may be required for elevated temperature applications when field induced anisotropy is critical for performance.

Phase evolution and field-induced magnetic anisotropy of the nanocomposite three-phase fcc, hcp, and amorphous soft magnetic alloy Co89Zr7B4

Crystallization and field-induced magnetic anisotropy were investigated for a Co89Zr7B4 alloy. A mixture of nanocrystalline fcc and hcp phases surrounded by an amorphous matrix is present after primary crystallization. For annealing in a 2T transverse field, the observed anisotropy fields and field-induced anisotropies are HK∼12–15Oe and KU∼550–680J∕m3 for field annealed amorphous ribbons as compared to HK∼18–19Oe and KU∼800–850J∕m3 for field crystallized ribbons. In comparison with the corresponding Fe-based alloy, the relatively high Curie temperature and large field-induced anisotropy of the field annealed amorphous ribbons indicate that the intergranular amorphous phase may provide a relatively more significant contribution to the field-induced anisotropy of Co-based nanocomposite ribbons such as Co89Zr7B4.

High Induction, Low Loss FeCo-Based Nanocomposite Alloys With Reduced Metalloid Content

We present a comparative study of reductions in metalloid and early transition metal content aimed at increasing inductions in FeCo-based nanocomposite alloys. Metalloid B and early transition metal Nb glass formers were replaced with magnetic late transition metals to determine the limits of amorphous and nanocrystalline formation and increase the magnetic flux density. Alloys of composition (Fe65Co35)80+x+yB13-xNb4-ySi2Cu1 (x=0-3, y=0,3) were cast by melt-spinning 50g batches into 2.5 mm wide, 30 μm thick ribbons. Ribbons were nanocrystallized and screened for their magnetic flux densities. The highest magnetic flux density of 1.85 T for quality ribbon was realized for the alloy with x=1, y=3. Magnetization as a function of temperature is reported for amorphous alloys to illustrate the effects of metalloid and early transition metal content on high temperature stability of magnetic properties and crystallization temperatures. Notable alloys were also synthesized by planar flow casting into 2.54 cm wide, 20 μ m ribbons and annealed under a 2.0 T transverse magnetic field. AC magnetic property measurements include permeability, coercive field, and core loss. The x=3, y=0 alloy demonstrated low core loss of 5.1 W/kg under a 0.2 T field and 20 kHz frequency with a high flux density of 1.70 T.

Increased induction in FeCo-based nanocomposite materials with reduced early transition metal growth inhibitors

We report on new high-saturation induction, high-temperature nanocomposite alloys with reduced glass formers. The amounts of the magnetic transition metals and early transition metal growth inhibitors were systematically varied to determine trade-offs between higher inductions and fine microstructures with consequently lower magnetic losses. Alloys of nominal composition (Fe65Co35)79.5+xNb4−xB13Si2Cu1.5 (x=0–4) were cast into a 28 mm wide, 20 μm thick ribbon from which toroidal cores were wound. Inductions and magnetic losses were measured after nanocrystallization and stress relief. We report technical magnetic properties: permeability, maximum induction, remanence ratio, coercive field, and high frequency magnetic losses as a function of composition and annealing temperature for these alloys. Of note is the development of maximum inductions in excess of 1.76 T in cores made of alloys with the x=4 composition and maximum inductions in excess of 1.67 T in alloys with the x=3 composition, which also exhibi...

Crystallization and thermomagnetic treatment of a Co-rich Co–Fe–Ni–Zr–B–Cu based nanocomposite alloy

The magnetic properties observed after various thermal-magnetic treatments for a (Co0.85Fe0.15)83.6Ni4.4Zr7B4Cu1 alloy are compared with those for a (Co0.88Fe0.12)79.4Nb2.6Si9B9 alloy of similar Co:Fe ratio which exhibited a large field induced anisotropy in previous work. The qualitative conclusions arrived at here also apply to the (Co0.85Fe0.15)88Zr7B4Cu1 alloy without Ni. For the transverse magnetic field annealed (Co0.85Fe0.15)83.6Ni4.4Zr7B4Cu1 alloy, the highest anisotropy fields HK (HK∼35–40Oe), field induced anisotropies KU (KU∼1700–2000J∕m3), and lowest coercivities HC (HC∼0.5–1.5Oe at f=3kHz) were observed for field annealed amorphous ribbons as compared to field crystallized ribbons. For the (Co0.88Fe0.12)79.4Nb2.6Si9B9 alloy, the field induced anisotropy is a maximum for field crystallized ribbons (HK∼28–45Oe, KU∼800–1800J∕m3) and the increase in dynamic coercivity (HC∼0.5–1Oe at f=3kHz) observed upon crystallization is much less dramatic. The field annealed amorphous alloy of composition (Co0...

Induced anisotropy in FeCo-based nanocomposites: Early transition metal content dependence

Soft magnetic nanocomposites variants of FeCo-based (HTX002) alloys (Fe65Co35)81+xB12Nb4−xSi2Cu1, exhibiting high inductions (up to 1.9 T), low losses, and high temperature stability are studied for high frequency inductors and current sensors. For alloys with x = 0, 1, 1.5, 2, and 3, we report field induced anisotropy, KU, after annealing at temperatures of 340–450 °C for 1 h in a 2 T transverse magnetic field. The anisotropy field, HK, measured by AC permeametry on toroidal cores, and by first order reversal curves on square sections of ribbon, decreases with annealing temperature and saturates at high annealing temperatures suggesting a nanostructure related anisotropy mechanism in which the amorphous phase exhibits a higher HK than the crystalline phase. A high saturation induction nanocrystalline phase and high HK amorphous phase were achieved by low temperature annealing resulting in a value of KU exceeding 14 × 103 erg/cm3, more than twice that reported previously for Fe-rich amorphous and nanocomp...

Secondary crystallization in (Fe65Co35)79.5+xB13Nb4−xSi2Cu1.5 and (Fe65Co35)83B10Nb4Si2Cu1 nanocomposite alloys

Here, secondary crystallization kinetics of high induction, low loss HTX002-type nanocompositealloys with the compositions (Fe65Co35)79.5+xB13Nb4−xSi2Cu1.5 (x = 0-4) and (Fe65Co35)83B10Nb4Si2Cu1 are reported. The magnetization of the alloys was measured through the thermal cycle of 50 °C-700 °C-300 °C-800 °C-300 °C-900 °C-200 °C by vibrating sample magnetometry. In (Fe65Co35)79.5+xB13Nb4−xSi2Cu1.5alloys, the stability of the (Fe,Co,Nb)23B6 (23-6) phase is increased with increasing Nb content. In the x = 4 alloy, (Fe,Nb)2B is the only secondary crystalline phase to form, demonstrating that Nb is necessary for the 23-6 phase to form. The (Fe65Co35)83B10Nb4Si2Cu1alloy forms the 23-6 phase more readily than the x = 0 alloy, likely due to the lower B content. The kinetics of secondary crystallization are important to assess long-term ageing effects on the metastable microstructure at elevated temperatures.

Stress induced anisotropy in CoFeMn soft magnetic nanocomposites

The use of processing techniques to create magnetic anisotropy in soft magnetic materials is a well-known method to control permeability and losses. In nanocomposite materials, field annealing below the Curie temperature results in uniaxial anisotropy energies up to ∼2 kJ/m3. Higher anisotropies up to ∼10 kJ/m3 result after annealing Fe-Si compositions under stress due to residual stress in the amorphous matrix acting on body centered cubic crystals. This work describes near zero magnetostriction Co80−x−yFexMnyNb4B14Si2 soft magnetic nanocomposites, where x and y < 8 at.% with close packed crystalline grains that show stress induced anisotropies up to ∼50 kJ/m3 and improved mechanical properties with respect to Fe-Si compositions. Difference patterns measured using transmission X-ray diffraction show evidence of affine strain with respect to the stress axis.