Compendium

Magnetic and Optical Materials

14 min read

Magnetic and Optical Materials

Tier 3 family index for two functional-materials domains driven by physics-level properties rather than bulk mechanical behavior: magnetism (hard, soft, and spintronic) and optics (glasses, crystals, laser gain media, fibers, and coatings). Both fields have well-developed commercial supply chains tied closely to a small number of specialty manufacturers.

1. Magnetic Materials

1.1 Hard magnetic materials (permanent magnets)

Permanent magnets are characterized by:

  • (BH)_max — maximum energy product in MGOe (mega-gauss-oersted) or kJ·m⁻³; figure of merit for stored magnetic energy.
  • B_r — remanence (T).
  • H_c — intrinsic coercivity (kA·m⁻¹ or kOe).
  • T_max — maximum service temperature, set by Curie temperature and irreversible-loss thresholds.

Nd-Fe-B (Nd₂Fe₁₄B)

The dominant high-performance permanent magnet, developed independently by Sagawa (Sumitomo Special Metals, Japan) and Croat (General Motors, US) in 1984, both targeting an alternative to Co-rare-earth magnets after the late-1970s cobalt price crisis.

  • Energy product: 35-55 MGOe (commercial grades up to N52, N55).
  • Remanence: ~1.4 T.
  • Curie temperature: ~310 °C (lower than SmCo).
  • Service temperature: 80-200 °C depending on grade; Dy or Tb diffusion grain-boundary treatment extends service T at modest expense in remanence.
  • Price: $80-120/kg sintered N52 (2024); volatile with Nd / Pr / Dy oxide spot price.
  • Production: ~135 kt/yr Nd₂Fe₁₄B globally (2024); ~60% from China; criticality concerns drove the US DPA Title III investment in MP Materials’ Mountain Pass mine + Texas magnet plant.

Producers:

  • JL MAG Rare-Earth (Ganzhou, China) — world’s largest by tonnage.
  • Hitachi Metals (now Proterial) (Japan) — original Sagawa licensee.
  • Shin-Etsu Chemical (Japan).
  • TDK (Japan).
  • ZK Crown (China).
  • Daido Electronics (Japan).
  • VAC Vacuumschmelze (Hanau, Germany) — EU’s largest.
  • Magnequench (now part of Neo Performance Materials, Canada / Thailand) — bonded magnet powders (MQP) for netshape parts.
  • Arnold Magnetic Technologies (US).
  • Schaeffler MD-MOTOR (EU; ramping for EV motors).

Raw material supply chain:

  • Lynas Rare Earths (Mt. Weld, Western Australia; processing in Kuantan, Malaysia and new Texas facility) — only major non-China NdPr separator.
  • MP Materials (Mountain Pass, California) — mine + on-site separation + Fort Worth, Texas magnet plant (operational 2025).
  • Iluka Resources — Australian rare-earth refinery in development at Eneabba.

SmCo (Sm-cobalt)

Older rare-earth magnet family; lower energy product than NdFeB but higher service temperature.

  • SmCo₅ (1:5) — Strnat 1966, first-generation; (BH)_max ~20 MGOe; T_max 250 °C.
  • Sm₂Co₁₇ (2:17) — second-generation; (BH)_max ~30 MGOe; T_max 350+ °C; magnets of choice for aerospace gyroscopes, traveling-wave-tube (TWT) focusing structures, and high-T motor service.
  • Producers: VAC, Arnold, Electron Energy Corporation, Hitachi Metals.

AlNiCo

1930s-era magnets (Mishima, 1931; Alcomax variants in the 1940s). Fe-Al-Ni-Co-Cu alloys; (BH)_max 5-9 MGOe; high T_max (500+ °C, the highest of common commercial magnets); poor coercivity. Used in legacy guitar pickups (Fender, Gibson stratocaster pickups), some measurement instruments, and high-T sensors where coercivity is not critical. Producers: Arnold, Aimangz, OuMag.

Ferrite (Sr / Ba hexagonal hard ferrite)

SrFe₁₂O₁₉ and BaFe₁₂O₁₉ M-type hexagonal ferrite; (BH)_max 3-4 MGOe; cheapest permanent magnet; ~90% of world magnet tonnage by weight. Applications: toys, motors, speakers, refrigerator magnets, holding magnets, MRI cosmetic gradient correction. Producers: Hitachi Metals, TDK, Steward, Magnetic Component Engineering.

Bonded vs. sintered

  • Sintered — pressed and sintered above 1000 °C; highest (BH)_max; near-net-shape limited; can be ground or sliced post-sinter.
  • Bonded — magnetic powder + polymer (epoxy, PA-12, PPS); injection-molded into complex netshape (rotor inserts, sensor magnets); lower (BH)_max (~10-15 MGOe for bonded NdFeB) but design freedom.

1.2 Soft magnetic materials

Low coercivity, high permeability, low core loss. Application priorities: transformer cores, motor laminations, inductors, magnetic shielding, EMI suppression.

Silicon steel (electrical steel)

The most magnetically optimized industrial material ever produced. 1.5-3% Si in Fe lowers eddy-current losses (Si raises resistivity); above 3% Si the alloy becomes too brittle to roll. Annual production ~17 million tonnes/yr globally.

  • Grain-oriented (Hi-B) — Goss texture, {110}<001>; for power-frequency transformers (50/60 Hz); core loss ~0.9-1.2 W/kg at 1.7 T / 50 Hz; producers: Allegheny / AK Steel (now part of Cleveland-Cliffs), Nippon Steel, Voestalpine, JFE Steel, ThyssenKrupp, POSCO.
  • Non-oriented (NO) — random texture; for rotating machines (motors, generators) where flux direction is uncertain; thinner 0.10-0.30 mm; thinner gauges for EV traction motors (35NO230, 25NO230 — Nippon Steel and JFE high-grade).

Nickel-iron permalloys

  • Permalloy 80 — Ni₈₀Fe₂₀; μ_r ~ 100,000 - 200,000; very low coercivity; magnetic shielding (μ-metal cans for sensitive instruments).
  • 78 Permalloy — Ni₇₈Fe₂₂ + Mo + Cu for improved manufacturability.
  • Supermalloy — Ni₇₉Mo₅Fe₁₆; μ_r > 1,000,000 in lab samples.
  • Mu-metal — Ni₇₅Cu₂Cr₂Fe₂₀ + Mo₅; commercial magnetic shield (Magnetic Shield Corp, Amuneal, Vacuumschmelze Mu-Metall).

Iron-silicon-aluminum (Sendust)

Fe-9.5%Si-5.5%Al alloy; lower loss than permalloy at higher frequency; used in audio recording heads (legacy) and high-frequency inductor cores.

Amorphous (Metglas)

Rapidly-quenched (~10⁶ K·s⁻¹) ribbon, no crystalline order; magnetic properties without grain-boundary or anisotropy losses. Iron-based (Fe-Si-B), cobalt-based (Co-Fe-Si-B), nickel-based.

  • Metglas 2605SA1 (Fe₇₈Si₁₃B₉) — distribution transformer cores; core loss ~0.2 W/kg at 60 Hz / 1.3 T — one-third the loss of grain-oriented Si steel.
  • Producer: Hitachi Metals (Metglas brand, Conway, SC, since 1979 spinoff of Allied Chemical).

Nanocrystalline (Finemet, Nanoperm)

Yoshizawa, Hitachi Metals, Journal of Applied Physics 64, 6044 (Dec 1988) — Fe-Si-B-Nb-Cu rapidly quenched and partially crystallized into ~10 nm Fe-Si grains in an amorphous matrix. Lower loss than Metglas at high frequency.

  • Finemet (Hitachi Metals).
  • Vitroperm 500F, 800F (VAC Vacuumschmelze).
  • Nanoperm (Magnetec).
  • Applications: high-frequency power electronics, common-mode chokes, EMI/RFI suppression, current transformers.

Soft ferrite

  • MnZn ferrite — μ_r 1,000 - 15,000; low loss at 100 kHz - 1 MHz; transformer cores in switching power supplies, EMI suppression. Producers: TDK, Ferroxcube, EPCOS, Magnetics Inc., Hitachi Metals.
  • NiZn ferrite — lower μ_r but extends to 100+ MHz; RF antennas, NFC, wireless charging Q-factor cores.

Powder cores

Iron-powder, Fe-Si-Al (Sendust), Ni-Fe-Mo (MPP — molybdenum permalloy powder), Fe-Si (Kool Mu), Fe-Ni (High Flux), Fe-Si-Cr (XFlux). Distributed-airgap structure suppresses saturation in DC-bias applications (inductors carrying DC current). Producers: Magnetics Inc., Mag-Inc, Sumida, Spang, Micrometals (US, original iron-powder maker), CSC, KDM Materials, AMOgreentech.

1.3 Spintronics

The use of electron spin in addition to charge for computing and memory.

  • GMR — giant magnetoresistance — Fert (Orsay) and Grünberg (Jülich) independently in 1988; ~10-20% resistance change in Fe/Cr multilayers; Nobel Prize Physics 2007. Commercialized in HDD read heads by IBM in 1997, enabling areal-density growth that took HDDs from 1 GB to TB scale. Current HDD areal density ~200 Gb/in² with TMR heads.
  • TMR — tunnel magnetoresistance — Julliere prediction 1975, Moodera demonstration 1995 with Al-O barriers; Parkin, IBM, Nature Materials 2004 with MgO barriers gave > 200% TMR ratio. MgO TMR is the basis of all modern HDD read heads and STT-MRAM.
  • STT-MRAM — spin-transfer-torque MRAM — write by passing spin-polarized current rather than external field; commercial: Everspin Technologies (Chandler, AZ) — 1 Gb discrete STT-MRAM; embedded MRAM in Samsung 28 nm eMRAM (2019) and GlobalFoundries 22FDX-MRAM.
  • SOT-MRAM — spin-orbit-torque MRAM — write current through heavy-metal underlayer (Ta, W, Pt); separates read and write paths; targeted by Apple, Intel, IBM for future cache memory.
  • Skyrmion racetrack memory — Parkin (IBM) 2008 proposal; magnetic-domain motion at sub-100-nm scale; research only.

1.4 Magnetocaloric materials

Materials with large adiabatic temperature change under applied magnetic field; foundation of magnetic refrigeration as an alternative to vapor-compression.

  • Gd₅(Si,Ge)₄ — Pecharsky-Gschneidner 1997; giant magnetocaloric effect at room temperature.
  • LaFe₁₃₋ₓSiₓ — La(Fe,Si)₁₃; cheaper than Gd; first-order transition near room T; H-doped variants tune T_C.
  • MnFeP₁₋ₓAsₓ, MnFeP₁₋ₓSiₓ — As-free Mn-Fe-P-Si alternatives.
  • Commercial demos: Astronautics Corporation of America (US Navy refrigerator project), Cooltech Applications (France; now defunct), Camfridge (UK), GE Appliances prototype magnetic refrigerator 2014.

2. Optical Materials

2.1 Optical glass

  • Schott AG (Mainz, Germany) — N-BK7 borosilicate (the most common reference glass; n_d ≈ 1.5168, V_d ≈ 64.2), F2 / SF2 dense flints, SF11 dense flint, LASF35 lanthanum heavy flint, N-LAK10, Borofloat 33 (borosilicate float glass for photolithography substrates), Duran (borosilicate process glassware, Pyrex equivalent in Europe).
  • Corning — Eagle XG LCD substrate (alkali-free), Lotus NXT OLED glass, Gorilla Glass V7 and Victus 2 (chemically strengthened aluminosilicate cover glass for Apple iPhone, Samsung Galaxy, Google Pixel), ULE titanium silicate (ultra-low-expansion, used for Hubble Space Telescope primary mirror and JWST primary segments — CTE < 30 ppb/K), HPFS fused silica (193 nm immersion lithography optics).
  • AGC (Asahi Glass) and Pilkington (NSG) — float architectural and automotive glass; LCD substrates.
  • Ohara (Japan) — S-FPL51, S-FPL53 fluorocrown low-dispersion (apochromat triplets), S-TIM dense flints.
  • Hoya — FCD100, FCD600 fluorocrown.
  • CDGM (China) and Sumita (Japan) — Schott / Ohara equivalents in their catalog.

Common glass codes a working optical engineer recognizes: N-BK7, N-SF11, N-LASF35, N-LAK10, F2, SF11, S-LAH53.

2.2 Optical crystals

  • Calcite (CaCO₃) — birefringent (Δn = 0.172); Glan-Thompson, Glan-Taylor, Wollaston polarizing prisms; sourced from Iceland spar deposits.
  • Quartz (α-SiO₂) — birefringent; waveplates (zero-order and multi-order); piezoelectric for oscillators.
  • MgF₂ — UV-transparent (down to 110 nm); AR coatings (single-layer V-coat); excimer-laser optics windows.
  • CaF₂ — VUV / DUV transparent; 193 nm and 157 nm lithography optics (Schott Lithotec, Hellma).
  • LiF, BaF₂ — VUV windows.
  • Sapphire (α-Al₂O₃) — Mohs 9 hardness; transparent 0.15 - 5.5 µm; high-power laser windows, harsh-environment viewports, military FLIR domes; producers: Crystal Systems (now GTAT / Mostostal), Saint-Gobain Sapphire, Monocrystal, Rubicon Technology, KYOCERA.
  • Silicon and germanium — IR-transmissive (Si: 1.2-15 µm; Ge: 2-14 µm); thermal-imaging optics (FLIR/Teledyne, Lynred, Lockheed Martin).
  • ZnSe and ZnS — mid-IR (0.6-21 µm for ZnSe; 0.4-12 µm for ZnS); CO₂-laser optics (II-VI Coherent CVD ZnSe).
  • CdTe — IR; X-ray detectors.
  • KBr, KCl, NaCl — IR windows and FTIR cells; hygroscopic.
  • KDP (KH₂PO₄) — nonlinear optical (NLO) crystal; second-harmonic generation (SHG) at 1064 → 532 nm; large boule sizes (NIF ICF crystals); supplier: Cleveland Crystals (now II-VI Coherent), Castech, EKSMA Optics.
  • LBO (LiB₃O₅) — NLO for SHG and THG; Crystal Laser, Castech.
  • BBO (β-BaB₂O₄) — NLO for UV down to ~190 nm; SHG, THG, FHG, OPA pump.
  • LN (LiNbO₃) — electro-optic modulators (telecom Mach-Zehnder modulators; Lumentum, Sumitomo Osaka Cement); periodically-poled PPLN for SHG/SFG; thin-film LN integrated photonics emerging (HyperLight, Lightium, NanoLN).
  • KTP (KTiOPO₄) — workhorse for 1064 → 532 nm green-laser pointers and DPSS green lasers.
  • GdYCOB, YCOB, LiCAF — newer NLO crystals.

2.3 Phosphors

Light-emitting inorganic powders excited by UV, blue, or electron beams.

  • YAG:Ce (Y₃Al₅O₁₂:Ce³⁺) — yellow phosphor; absorbs 450 nm blue LED, emits broad yellow (550 nm); blue + yellow = white LED. Used by Nichia (inventor of blue LED + YAG:Ce white LED route, Nakamura Nobel 2014), Lumileds, Osram Opto Semiconductors (now ams Osram), Cree (now Wolfspeed), Mitsubishi Chemical.
  • LuAG:Ce (Lu₃Al₅O₁₂:Ce) — green phosphor; also used in PET scintillators.
  • GAGG (Gd₃Al₂Ga₃O₁₂:Ce) — fast scintillator for PET, SPECT.
  • SiAlON nitrides — α-SiAlON:Eu (yellow-orange), β-SiAlON:Eu (green) — Mitsubishi Chemical, Intematix; high-quantum-yield red and green for high-CRI LEDs.
  • CASN (CaAlSiN₃:Eu) — red nitride phosphor; high efficiency at high temperature.
  • KSF / PFS (K₂SiF₆:Mn⁴⁺) — narrow-band red phosphor; ~10 nm FWHM at 632 nm; GE Current TriGain technology; raises color gamut of LCD displays (~90% BT.2020).
  • SrAl₂O₄:Eu²⁺,Dy³⁺ — long-afterglow “glow-in-the-dark” phosphor; emergency signage, watch dials.

2.4 Laser gain media

  • Ti:Sapphire (Ti³⁺:Al₂O₃) — Moulton (Schwartz Electro-Optics) 1986; tunable 670-1100 nm; basis of all modern femtosecond solid-state lasers (~10 fs achievable). Vendors: Coherent (Verdi pump + Mira / Vitara / Mantis oscillators; Legend / Astrella amplifiers), Spectra-Physics (now MKS; Tsunami, Mai Tai, Solstice), Light Conversion, KMLabs.
  • Nd:YAG (Nd³⁺:Y₃Al₅O₁₂) — Geusic-Marcos-Van Uitert (Bell Labs) 1964; 1064 nm; the workhorse industrial DPSS laser host.
  • Nd:YVO₄ — higher absorption cross-section than YAG; common in DPSS green pointers.
  • Yb:YAG — 1030 nm; high efficiency for thin-disk industrial lasers (Trumpf, Coherent Dilas).
  • Yb-doped fibers — basis of fiber lasers; IPG Photonics dominates the industrial fiber-laser market with 30 kW+ continuous-wave 1070 nm systems for cutting and welding; competitors: nLight, Coherent (Lumera + Rofin), Maxphotonics, Raycus.
  • Er-doped fibers (EDFA) — 1530-1565 nm telecom amplifiers; pumped at 980 nm; Lumentum, II-VI Coherent, Bookham (now Lumentum) dominate the telecom amplifier component market.
  • Er:YAG — 2940 nm — strong water absorption; dental, dermatology (laser skin resurfacing — Lumenis, Sciton).
  • Tm-doped fiber — 1.9-2.1 µm “eye-safe” wavelength region for LIDAR and medical.
  • Ho:YLF, Ho:YAG — 2.06 µm; medical lithotripsy.
  • CTH:YAG (Cr:Tm:Ho:YAG) — 2.1 µm.
  • Ruby (Cr³⁺:Al₂O₃) — Maiman (Hughes Aircraft) 1960 — the first operational laser at 694 nm; now historical.
  • Gas lasers — HeNe (633 nm), Ar-ion (488/514 nm; declining), CO₂ (10.6 µm, industrial), KrF excimer (248 nm — DUV lithography), ArF excimer (193 nm — DUV immersion lithography), F₂ (157 nm).
  • Semiconductor diode lasers — GaAs / AlGaAs / InGaAs / InP / GaN heterostructures (see semiconductor-materials); VCSEL (vertical-cavity surface-emitting; Lumentum, Trumpf Photonics, II-VI Coherent — for datacenters, smartphone face-ID); QCL — quantum cascade laser (Capasso et al. at Bell Labs 1994; mid-IR 3-25 µm; Hamamatsu, Thorlabs, Block Engineering, AdTech Optics, Daylight Solutions, mirSense).

2.5 Optical fibers

  • Silica SMF-28 — Corning’s single-mode telecom fiber; G.652 standard; ~$0.005/m wholesale (2024) at 100 km drum quantity.
  • G.657 bend-insensitive — Corning ClearCurve, Fujikura, Sumitomo; FTTH last-drop.
  • Multi-mode — OM3, OM4, OM5 50-µm-core; data-center; 850 nm LED/VCSEL-source.
  • Fluoride fiber (ZBLAN, ZrF₄-BaF₂-LaF₃-AlF₃-NaF) — transmits 0.3 - 5.5 µm; mid-IR delivery, supercontinuum source; suppliers: Le Verre Fluoré (France), Thorlabs (US, acquired Fiberlabs).
  • Chalcogenide fiber (As₂S₃, As₂Se₃) — 1-10 µm mid-IR delivery; IRflex, Coractive.
  • PCF — photonic crystal fiber — Russell (Bath/Erlangen) 1996; microstructured air-hole cladding; supercontinuum, high power, single-mode any wavelength. Suppliers: NKT Photonics (Birkerod, Denmark; market leader), Coractive (Canada), Thorlabs.
  • Hollow-core fiber — light propagates in air; lower loss and lower latency than silica; Microsoft acquired Lumenisity (Romsey, UK) in 2022 for hollow-core production; deployed in financial trading trans-Atlantic links for sub-millisecond latency saving over standard SMF.

2.6 Coatings and thin films

  • AR (anti-reflection) — single-layer MgF₂ V-coat; multi-layer broadband BBAR (Edmund Optics, Newport, Thorlabs).
  • HR (high reflectivity) — alternating high-low-index dielectric stacks (TiO₂ / SiO₂, Ta₂O₅ / SiO₂); R > 99.9999% achievable for laser-cavity mirrors; ion-beam-sputtered (IBS) for lowest absorption (Layertec, Edmund Optics, II-VI Coherent, Manx Precision Optics).
  • Dichroic / dichroic mirrors — wavelength-selective reflection; common in fluorescence microscopy (Chroma Technology, Semrock / IDEX Health & Sciences).
  • Notch filters and edge filters — Raman spectroscopy (Semrock SuperNotch).

2.7 Nonlinear optics

For nonlinear-optical crystals see Section 2.2. Process: SHG (second-harmonic), THG (third-harmonic), FHG (fourth-harmonic), SFG (sum-frequency), OPA / OPO (optical parametric amplifier / oscillator).

CPA — chirped pulse amplification — Mourou (Michigan) and Strickland (Rochester / Waterloo) 1985 — stretch, amplify, recompress ultrashort pulses; Nobel Prize Physics 2018. Required: dispersive grating stretchers/compressors (KDP gratings or fused-silica gratings), Ti:Sapphire or Yb:YAG amplifiers; enables PW-class laser systems (ELI Beamlines, BELLA, NIF advanced shots).

2.8 Display materials

  • LCD glass — Corning Eagle XG, AGC, NEG.
  • OLED — small-molecule (Tang and Van Slyke, Kodak, 1987); polymer PLED (Friend, Cambridge, 1990); phosphorescent (Forrest-Thompson, 1998) — 25% → near-100% IQE. UDC (Universal Display Corp) — dominant patents on phosphorescent emitters; supplies red and green PHOLED dopants to Samsung Display, LG Display.
  • WOLED, RGB OLED — Samsung Display (RGB), LG Display (WOLED).
  • µLED / Mini-LED / microLED — directly-emissive sub-100-µm inorganic LEDs; Apple Vision Pro displays use Sony Semiconductor microOLED, future Apple roadmap to microLED.

2.9 Photonics

  • Silicon photonics — CMOS-compatible passive and modulator structures; Intel Silicon Photonics 100/400G; IBM Si photonics; GlobalFoundries 90/45 nm SiP process; Ayar Labs co-packaged optics in NVIDIA Quantum-X800 InfiniBand switch (2024).
  • III-V on Si — Lightmatter, Lightium, Rockley Photonics — hybrid III-V/SiP for higher gain.

2.10 Suppliers (catalog optics and photonics)

  • Thorlabs — broadest catalog optics, mounts, fibers; market leader by SKU count.
  • Edmund Optics — catalog optics, custom lenses, prisms.
  • Newport (MKS Instruments) — vibration isolation tables, motion stages, photonics components.
  • II-VI Coherent (Coherent + II-VI merger 2022) — laser systems and optics.
  • Lumentum — telecom and 3D-sensing lasers, EDFA components.
  • Hamamatsu Photonics — PMTs, APDs, Si photodiodes, InGaAs photodiodes, MEMS scanners.
  • First Sensor (TE Connectivity) — Si and InGaAs detectors.
  • Excelitas Technologies — photodetectors, flash lamps, xenon arc.
  • Eblana Photonics — DFB diode lasers for sensing.

Adjacent notes

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