^{1,a)}, E. A. Lass

^{2}, S. J. Poon

^{1}, G. J. Shiflet

^{2}, M. Rawlings

^{3}, M. Daniil

^{4}and M. A. Willard

^{5}

### Abstract

A series of ferromagnetic metallic glasses with compositions (Fe,Co)_{78}Mo_{1}(B,P,Si)_{21} are shown to possess good thermal stability and soft magnetic performance. The thermal stability inside the supercooled liquid temperature region was evaluated using Kissinger analysis of primary crystallization, time-temperature-transformation (TTT) diagrams, and the extent of the supercooled liquid region (Δ*T* _{ x }). The phosphorus-free alloy, Fe_{78}Mo_{1}B_{15}Si_{6}, had an activation energy (*E* _{ a }) of 414 kJ/mol, Δ*T* _{ x } ∼ 50 K, and began devitrifying after about 1 min at 730 K. By way of comparison, the phosphorus-containing alloy, Fe_{78}Mo_{1}B_{13}P_{6}Si_{2}, had an *E* _{ a } of 440 kJ/mol, Δ*T* _{ x } ∼ 45 K, and began devitrification after 10 min at 730 K. High saturation magnetization (μ_{ 0 } *M* _{ s } ∼ 1.45-1.55 T) and low coercivity (*H* _{ c } ∼ 20 A/m) are demonstrated across the composition range. Core loss measurements of toroidal cores are shown to be less than 12 W/cm^{3} at 1 T, maximum induction amplitude (under both sinusoidal and square waveforms). Trends were established for magnetic and thermal stability as a function of metalloid and magnetic transition metal composition.

M. Rawlings acknowledges summer internship support from the National Science Foundation under grant, DMR-0648917. M. A. Willard gratefully acknowledges support from the Office of Naval Research. The research at UVA is supported by ONR (Contract No. N00014-07-C0-0550). The authors thank Dr. Luana Iorio and Dr. Frank Johnson of GE Global Research Center for discussion and critical reading of the manuscript.

I. INTRODUCTION

II. EXPERIMENTAL PROCEDURES

III. RESULTS AND DISCUSSION

A. Thermal stability

B. Magnetic properties

IV. CONCLUSIONS

### Key Topics

- Amorphous metals
- 30.0
- Metalloids
- 19.0
- Thermal stability
- 18.0
- Curie point
- 17.0
- Crystallization
- 14.0

##### B01D9/00

##### C22C19/00

##### C22C38/00

##### C22C45/00

##### H01F1/00

##### H01F1/12

##### H01F13/00

## Figures

(a) Differential scanning calorimetric curves for (Fe_{1-x }Co_{ x })_{78}Mo_{1}B_{21-y-z }P_{ y }Si_{ z } alloys with *x* = 0 and {*y*,*z*} = {0,6}, {6,2}, {6,6}, and {6,10}. The upward and downward arrows indicate *T* _{ c } and *T* _{ g }, respectively. (b) Ternary diagram showing the Δ*T* _{ x } dependence (in K) on metalloid composition in the Fe_{78}Mo_{1}(B,P,Si)_{21} alloy series, with compositions indicated as {y,z}.

(a) Differential scanning calorimetric curves for (Fe_{1-x }Co_{ x })_{78}Mo_{1}B_{21-y-z }P_{ y }Si_{ z } alloys with *x* = 0 and {*y*,*z*} = {0,6}, {6,2}, {6,6}, and {6,10}. The upward and downward arrows indicate *T* _{ c } and *T* _{ g }, respectively. (b) Ternary diagram showing the Δ*T* _{ x } dependence (in K) on metalloid composition in the Fe_{78}Mo_{1}(B,P,Si)_{21} alloy series, with compositions indicated as {y,z}.

Glass transition (*T* _{ g }) and crystallization temperatures (*T* _{ x }) plotted against the phosphorus content of the alloy (*y*). Difference between the curves is Δ*T* _{ x }, which ranges from about 50 (at *y* = 0) to about 40 (at *y* = 10).

Glass transition (*T* _{ g }) and crystallization temperatures (*T* _{ x }) plotted against the phosphorus content of the alloy (*y*). Difference between the curves is Δ*T* _{ x }, which ranges from about 50 (at *y* = 0) to about 40 (at *y* = 10).

Partial time-temperature-transformation (TTT) diagram of (a) Fe_{78}Mo_{1}B_{13}P_{6}Si_{2} (i.e., {0,6,2}) and (b) Fe_{78}Mo_{1}B_{15}Si_{6} (i.e., {0,0,6}) metallic glasses in the SCL region. The single-phase amorphous and mixed crystalline/amorphous phases are marked in these diagrams with square and circle symbols, respectively. (c) The comparison of crystallization of the two alloys plotted on the same diagram.

Partial time-temperature-transformation (TTT) diagram of (a) Fe_{78}Mo_{1}B_{13}P_{6}Si_{2} (i.e., {0,6,2}) and (b) Fe_{78}Mo_{1}B_{15}Si_{6} (i.e., {0,0,6}) metallic glasses in the SCL region. The single-phase amorphous and mixed crystalline/amorphous phases are marked in these diagrams with square and circle symbols, respectively. (c) The comparison of crystallization of the two alloys plotted on the same diagram.

A characteristic hysteresis loop for the Fe_{78}Mo_{1}B_{15}Si_{6} (i.e., {0,0,6}) sample, measured at room temperature with a maximum applied field of 72 kA/m. The inset shows an enlargement of the loop near zero field to highlight the coercivity.

A characteristic hysteresis loop for the Fe_{78}Mo_{1}B_{15}Si_{6} (i.e., {0,0,6}) sample, measured at room temperature with a maximum applied field of 72 kA/m. The inset shows an enlargement of the loop near zero field to highlight the coercivity.

(a) Saturation magnetization (μ_{ 0 } *M* _{ s }) as a function of average magnetic valence for the Fe_{78}Mo_{1}(B,P,Si)_{21} alloy series. (b) Saturation magnetization plotted against Co content in the (Fe_{1-x }Co_{ x })_{78}Mo_{1}B_{21-y-z }P_{ y }Si_{ z } alloy series with {*y*,*z*} = {0,6}, {6,2}, {6,6}, and {6,10}. For comparison, data from the (Fe_{1-x }Co_{ x })_{80}B_{20} and (Fe_{1-x }Co_{ x })_{78}Mo_{1}(C,B,P,Si)_{21} alloy series are plotted from Refs. 22 and 25, respectively.

(a) Saturation magnetization (μ_{ 0 } *M* _{ s }) as a function of average magnetic valence for the Fe_{78}Mo_{1}(B,P,Si)_{21} alloy series. (b) Saturation magnetization plotted against Co content in the (Fe_{1-x }Co_{ x })_{78}Mo_{1}B_{21-y-z }P_{ y }Si_{ z } alloy series with {*y*,*z*} = {0,6}, {6,2}, {6,6}, and {6,10}. For comparison, data from the (Fe_{1-x }Co_{ x })_{80}B_{20} and (Fe_{1-x }Co_{ x })_{78}Mo_{1}(C,B,P,Si)_{21} alloy series are plotted from Refs. 22 and 25, respectively.

(a) Curie temperature (*T* _{ c }) plotted against the average metalloid atomic radius for the Fe_{78}Mo_{1}(B,P,Si)_{21} alloy series. Atomic radii are marked for the metalloid atoms B, P, and Si. (b) Curie temperature variation with Co content for the full series of alloys studied.

(a) Curie temperature (*T* _{ c }) plotted against the average metalloid atomic radius for the Fe_{78}Mo_{1}(B,P,Si)_{21} alloy series. Atomic radii are marked for the metalloid atoms B, P, and Si. (b) Curie temperature variation with Co content for the full series of alloys studied.

Core loss plotted against switching frequency for the alloy Fe_{78}Mo_{1}B_{15}Si_{6} at magnetic induction amplitudes from 100 to 1000 mT. (a) Sine waveform, (b) square waveform.

Core loss plotted against switching frequency for the alloy Fe_{78}Mo_{1}B_{15}Si_{6} at magnetic induction amplitudes from 100 to 1000 mT. (a) Sine waveform, (b) square waveform.

Core loss plotted against maximum induction amplitude at a switchingfrequency of 20 kHz (sine waveform) for Fe_{78}Mo_{1}B_{15}Si_{6},Fe_{78}Mo_{1}B_{13}P_{6}Si_{2}, (Fe_{0.85}Co_{0.15})_{78}Mo_{1}B_{15}Si_{6}, and (Fe_{0.85}Co_{0.15})_{78}Mo_{1}B_{13}P_{6}Si_{2}.

Core loss plotted against maximum induction amplitude at a switchingfrequency of 20 kHz (sine waveform) for Fe_{78}Mo_{1}B_{15}Si_{6},Fe_{78}Mo_{1}B_{13}P_{6}Si_{2}, (Fe_{0.85}Co_{0.15})_{78}Mo_{1}B_{15}Si_{6}, and (Fe_{0.85}Co_{0.15})_{78}Mo_{1}B_{13}P_{6}Si_{2}.

## Tables

Summary of Curie temperature (*T* _{ c }), glass transition temperature (*T* _{ g }), onset temperature of crystallization (*T* _{ x }), saturation magnetization (*μ* _{ 0 } *M* _{ s }), and coercive field (H_{c}) for as-spun (Fe_{1-} _{ x }Co_{ x })_{78}Mo_{1}B_{21-y-} _{ z }P_{ y }Si_{ z } metallic glasses. The values of *T* _{ g } of some metallic glasses could not be obtained from DSC signals due to close proximity to *T* _{ c }.

Summary of Curie temperature (*T* _{ c }), glass transition temperature (*T* _{ g }), onset temperature of crystallization (*T* _{ x }), saturation magnetization (*μ* _{ 0 } *M* _{ s }), and coercive field (H_{c}) for as-spun (Fe_{1-} _{ x }Co_{ x })_{78}Mo_{1}B_{21-y-} _{ z }P_{ y }Si_{ z } metallic glasses. The values of *T* _{ g } of some metallic glasses could not be obtained from DSC signals due to close proximity to *T* _{ c }.

Summary of coefficients for the power-law relationship between core losses (*P* _{ cv }) and maximum magnetic induction amplitude (*B* _{ max }). The Steinmetz exponent (n) and power-law prefactor (*P* _{ 0 }) are reported for alloys measured by AC core loss measurements on toroidal-shaped cores using sine and square waveforms. Steinmetz equation: .

Summary of coefficients for the power-law relationship between core losses (*P* _{ cv }) and maximum magnetic induction amplitude (*B* _{ max }). The Steinmetz exponent (n) and power-law prefactor (*P* _{ 0 }) are reported for alloys measured by AC core loss measurements on toroidal-shaped cores using sine and square waveforms. Steinmetz equation: .

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