Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

The rise of graphene

Results of room-temperature Raman scattering studies of ultrathin graphitic films supported on Si (100)/SiO2 substrates are reported. The results are significantly different from those known for graphite. Spectra were collected using 514.5 nm radiation on films containing from n = 1 to 20 graphene layers, as determined by atomic force microscopy. Both the first- and second-order Raman spectra show unique signatures of the number of layers in the film. The nGL film analogue of the Raman G-band in graphite exhibits a Lorentzian line shape whose center frequency shifts linearly relative to graphite as ∼1/n (for n = 1 ωG ≈ 1587 cm-1). Three weak bands, identified with disorder-induced first-order scattering, are observed at ∼1350, 1450, and 1500 cm-1. The ∼1500 cm-1 band is weak but relatively sharp and exhibits an interesting n-dependence. In general, the intensity of these D-bands decreases dramatically with increasing n. Three second-order bands are also observed (∼2450, ∼2700, and 3248 cm-1). They are ana...

Raman Scattering from High-Frequency Phonons in Supported n-Graphene Layer Films

Much like the world described in Abbott's Flatland, graphene is a two-dimensional object. And, as ``Flatland'' is ``a romance of many dimensions,'' graphene is much more than just a flat crystal. It possesses a number of unusual properties which are often unique or superior to those in other materials. In this brief lecture I would like to explain the reason for my (and many other people's) fascination with this material, and invite the reader to share some of the excitement I've experienced while researching it.

https://link.aps.org/pdf/10.1103/RevModPhys.83.837

Nobel Lecture: Graphene: Materials in the Flatland

In spin-based electronics, information is encoded by the spin state of electron bunches Processing this information requires the controlled transport of spin angular momentum through a solid, preferably at frequencies reaching the so far unexplored terahertz regime Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures A laser pulse is used to drive spins from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter based on the inverse spin Hall effect, which converts the spin flow into a terahertz electromagnetic pulse We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters

Terahertz spin current pulses controlled by magnetic heterostructures.

We have developed a unique micromechanical method to extract extremely thin graphite samples. Graphite crystallites with thicknesses ranging from 10 to 100nm and lateral size ∼2μm are extracted from bulk. Mesoscopic graphite devices are fabricated from these samples for electric field-dependent conductance measurements. Strong conductance modulation as a function of gate voltage is observed in the thinner crystallite devices. The temperature-dependent resistivity measurements show more boundary scattering contribution in the thinner graphite samples.

Fabrication and electric-field-dependent transport measurements of mesoscopic graphite devices

The magnetic layer of a head structure can satisfy the characteristics of both the magnetic shield layer and magnetic pole layer for recording by bringing the combined upper part and lower part of the magnetic layer respectively into conformity with the widths necessary for the shield layer and for the magnetic pole, e.g., specifically, by disposing a taper or more specifically a step shape to the section of the magnetic layer to have the dimension of the upper part of the magnetic layer different from that of the lower part. The width of the magnetic layer facing one of the recording magnetic poles can be brought into conformity with the track width. Accordingly, the flux at the time of a write operation concentrates on the track width portion and hence, side writing of the recording head can be reduced. On the other hand, the width of the magnetic head on the opposed side to the magnetoresistive sensor can be extended sufficiently to fully cover the sensor. For this reason, the noise picked up by the magnetoresistive sensor resulting from the signal flux from the adjacent tracks can be reduced.

Integrated magnetic head having a magnetic layer functioning as both a magnetic shield and a magnetic pole

Magnetocapacitance effect of coercive differential spin tunneling junctions Co(100 A)/Al2O3(∼20 A)/Co(500 A) fabricated onto a glass substrate by ion-beam mask sputtering was investigated. The impedance was measured by a four-probe method at room temperature in the frequency range from 120 Hz to 1 MHz. It is found that the effective capacitance changes with the application of an external magnetic field. At high frequencies, the magnetocapacitance ratio is as large as the dc magnetoresistance ratio. However, at low frequencies, capacitance changes cannot be observed because the measurement sensitivity is too low. The magnetocapacitance effect was hence found to be a promising tool for high frequency magnetic sensing.

Magnetocapacitance effect of spin tunneling junctions

In a composite magnetic head comprising a magnetoresistive read head including a magnetic thin film having a magnetoresistive effect and soft magnetic members interposing the soft magnetic film between them through a non-magnetic insulation layer, an induction type write head including poles formed in a moving direction of a medium and a conductor crossing the poles, and disposed in the proximity of the magnetoresistive head, and a substrate supporting these heads, the present invention discloses a composite magnetic head characterized in that part of a floating surface inclusive of the magnetic head constituent members has recesses and the read/write operations to and from the medium are effected by the portion interposed by these recesses.

Narrow track thin film magnetic head suitable for high density recording and reproducing operations and fabrication method thereof wherein an air bearing surface has at least one groove containing a non-magnetic electrically conductive layer

PURPOSE: To obtain an amorphous thin film with low coercive force and high initial permeability by sputtering or vapor-depositing an alloy consisting of a nonmetallic element and a rare earth element replaced partially by a metallic element such as Ti, Zr or Hf and the balance essentially transition metallic element. CONSTITUTION: An alloy expressed by a formula M a T b X c Z d is prepared. In the formula M is ≥1 kind of element selected from Fe, Ni and Co, T is ≥1 kind of element selected from Mn, Cr, W, etc., X is ≥1 kind of element selected from Zr, Ti, Y, etc., Z is ≥1 kind of element selected from P, B, C, etc., a+b+c+d= 100, 0≤b≤95, 30≤a+b≤95, 0≤c≤70and 0≤d≤30. The alloy is sputtered or vapor-deposited to manufacture an amorphous thin film. This film is different from a conventional amorphous thin film in alloy composition and has high thermal stability. when the film is magnetized, it shows superior magnetic characteristics, that is, low coercive force and high permeability. COPYRIGHT: (C)1983,JPO&Japio

Manufacture of amorphous thin film

A multilayered ferromagnetic amorphous alloy film is constituted by a plurality of main ferromagnetic material alloy films of a ferromagnetic amorphous alloy laminated one upon another with a spacer ferromagnetic material layer interposed therebetween, the spacer ferromagnetic material layer being of a ferromagnetic material different from the ferromagnetic alloy. Also disclosed is a magnetic head employing the above-described multilayered film for, at least, a portion of a core thereof. The multilayered film has excellent magnetic characteristics and is easily patterned.

Kazuo Shiiki

Papers

Integrated magnetic head having a magnetic layer functioning as both a magnetic shield and a magnetic pole

Magnetocapacitance effect of spin tunneling junctions

Narrow track thin film magnetic head suitable for high density recording and reproducing operations and fabrication method thereof wherein an air bearing surface has at least one groove containing a non-magnetic electrically conductive layer

Manufacture of amorphous thin film

Multilayered ferromagnetic amorphous alloy film and magnetic head employing the same