Magnetic field generator

• US 8,780,677 B2
• Filed: 01/03/2013
• Issued: 07/15/2014
• Est. Priority Date: 01/06/2012
• Status: Expired due to Fees

• Current Assignee: University of Southampton
• Original Assignee: University of Southampton
• Inventors: Zheludev, Nikolay Ivanovich, Tsiatmas, Anagnostis, Stewart, William James, Fedotov, Vassili A, Garcia De Abajo, Francisco Javier
• Primary Examiner(s): BERNARDI, BRENDA C
• Application Number:
  US13/733,338
• Publication Number:
  US 20130176836A1
• Time in Patent Office: 558 Days
• Field of Search: 369/13.01, 369/13.02, 369/13.13, 369/13.14, 369/13.17, 360/59
• US Class Current: 369/13.17
• CPC Class Codes: G11B 13/04 magnetically or by magnetisation and optically or by radiation, for changing or sensing optical properties
• CPC Class Codes: G11B 2005/0021 Thermally assisted recording using an auxiliary energy source for heating the recording layer locally to assist the magnetization reversal
• CPC Class Codes: G11B 5/02 Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
• CPC Class Codes: G11B 5/127 Structure or manufacture of heads, e.g. inductive
• CPC Class Codes: H01L 31/102 characterised by only one potential barrier
• CPC Class Codes: H10N 10/854 comprising only metals H10N10/852, H10N10/853 take precedence

Abstract

A metallic ring is made of two metals, wherein one metal forms a major arcuate portion and the other a minor arcuate portion of the ring, thereby forming a thermocouple-type structure as a result of the two inter-metallic junctions. The metallic ring supports a surface plasmon whose energy is matched to the energy, i.e. wavelength, of an incident light beam so that the oscillating electromagnetic field of the light resonates with the plasmon. The resonating plasmon causes a temperature difference to arise between the two inter-metallic junctions in the ring. The different Seebeck coefficients of the two metals results in the temperature difference causing a net current to flow around the ring, which in turn generates a magnetic field. Such a thermoelectric metamaterial ring transforms high frequency optical energy into long duration magnetic radiation pulses in the terahertz range. Applications of these devices include high density magnetic recording, magnetic field spectroscopy, and efficient terahertz radiation sources.

Claims

1. A device for generating a magnetic field, comprising:

a light source operable to generate pulses of light of a particular wavelength, the light having an oscillating electromagnetic field with a defined polarization; and

a magnetic field generator arranged to receive the light and comprising a closed current path made of first and second angular arc portions of first and second materials interconnected by first and second junctions;

the closed current path comprising electrons or holes which absorb energy from each pulse of light and are thereby transiently heated; and

the polarization of the light being aligned relative to the closed current path so that each pulse of light causes different amounts of transient heating of the electrons or holes at the first and second junctions so that one of the junctions becomes hotter than the other, which causes a thermally induced transient current to flow around the closed current path, thereby generating a transient magnetic field.

2. The device of claim 1, wherein the first and second materials are metallic and have first and second Seebeck coefficients which are different and the first and second junctions are ohmic, and wherein the light is absorbed by a plasmon.

3. The device of claim 2, wherein the first and second junctions are separated angularly by approximately 90 degrees, wherein approximately indicates a range of one of ±

45 degrees.

4. The device of claim 1, wherein the first and second materials are semiconductors and the first and/or second junctions are p-n junctions, and wherein the resonance is between a valence band and a conduction band of at least one of the semiconductors.

5. The device of claim 1, wherein the first and second materials are metallic and the first and/or second junctions are metal-insulator-metal tunnel junctions formed by an insulator interposed between the first and second materials.

6. The device of claim 1, wherein the closed current path has a resonance of electron or hole oscillations at an energy matched to the wavelength of the light source so that in use the electrons or holes resonantly absorb energy from each pulse of light.

7. The device of claim 1, wherein the electrons or holes are transiently heated by each pulse to a temperature of at least 1000 Kelvin.

8. The device of claim 1, wherein the first and second materials have respective first and second electron-phonon scattering times characteristic of the principal cooling mechanism for hot electrons, and wherein the pulses have a duration shorter than either the first or second electron-phonon scattering time.

9. The device of claim 1, wherein the pulse duration is at least 2, 5, 10 or 20 times shorter than the shorter of the first and second electron-phonon scattering times.

10. The device of claim 1, wherein the closed current path is shaped as a single closed loop.

11. The device of claim 1, wherein the closed current path is shaped as first and second incomplete rings of different size joined together such that the interiors of the incomplete rings form connected spaces, wherein one of the incomplete rings is dimensioned to optimize the resonance and the other of the incomplete rings is dimensioned to optimize the transient magnetic field.

12. The device of claim 11, wherein further rings are provided with said ring so that the rings form an array, and wherein the light source is arranged to direct light to cover the array of rings, so that the array of rings collectively generates a transient electromagnetic field.

13. The device of claim 1, further comprising a cooling element in thermal connection with the field generator and operable to lower at least a part of the closed current path to a temperature at which it is superconducting.

14. The device of claim 1, further comprising a heat dissipation structure to assist removal of heat generated by the induced current.

15. A magnetic recording head having a write pole made from a magnetic field generating device comprising:

a light source operable to generate pulses of light of a particular wavelength, the light having an oscillating electromagnetic field with a defined polarization; and

a magnetic field generator arranged to receive the light and comprising a closed current path made of first and second angular arc portions of first and second materials interconnected by first and second junctions;

the closed current path comprising electrons or holes which absorb energy from each pulse of light and are thereby transiently heated; and

the polarization of the light being aligned relative to the closed current path so that each pulse of light causes different amounts of transient heating of the electrons or holes at the first and second junctions so that one of the junctions becomes hotter than the other, which causes a thermally induced transient current to flow around the closed current path, thereby generating a transient magnetic field.

16. A magnetic disc drive system comprising:

a magnetic recording medium comprising a large number of magnetic domains whose alignment is used to encode data;

a magnetic recording head having a write pole made from a magnetic field generating device comprising;

i. a light source operable to generate pulses of light of a particular wavelength, the light having an oscillating electromagnetic field with a defined polarization; and

ii. a magnetic field generator arranged to receive the light and comprising a closed current path made of first and second angular arc portions of first and second materials interconnected by first and second junctions;

iii. the closed current path comprising electrons or holes which absorb energy from each pulse of light and are thereby transiently heated; and

iv. the polarization of the light being aligned relative to the closed current path so that each pulse of light causes different amounts of transient heating of the electrons or holes at the first and second junctions so that one of the junctions becomes hotter than the other, which causes a thermally induced transient current to flow around the closed current path, thereby generating a transient magnetic field,

the magnetic recording head being movable over a surface of said magnetic recording medium in order to apply a local magnetic field greater than a recording coercive field of the magnetic recording medium to selected locations of the magnetic recording medium, thereby to define alignment of magnetic domains at those locations.

17. The magnetic disc drive system of claim 16, wherein the closed current path acts as a self-aligning mask to locally heat the magnetic recording medium and thereby provide heat assisted magnetic recording.

18. The magnetic disc drive system of claim 17, wherein the said light from the light source provides the local heating for the heat assisted magnetic recording.

19. The magnetic disc drive system of claim 16, wherein a common light routing path is provided to direct the said light from the light source and further light for the heat assisted magnetic recording.

20. The magnetic disc drive system of claim 16, wherein the magnetic domains are aligned according to the local magnetic field to encode the data being written.