Itsuko S. Suzuki

Measurement of mutual inductance from the frequency dependence of impedance of AC coupled circuits using a digital dual-phase lock-in amplifier

We present a simple method for determining the mutual inductance between two coils in a coupled AC circuit using a digital dual-phase lock-in amplifier. The frequency dependence of the real and imaginary parts is measured as the coupling is changed. The mutual inductance decreases as the distance d between the centers of coils is increased. We show that the coupling is proportional to d−n with n≈3. This coupling is similar to that of two magnetic dipoles.

H–T phase diagram and the nature of vortex-glass phase in a quasi-two-dimensional superconductor: Sn-metal layer sandwiched between graphene sheets

Abstract The magnetic properties of a quasi-two-dimensional (2D) superconductor, Sn-metal graphite (MG), are studied using DC and AC magnetic susceptibility. Sn-MG has a unique layered structure where Sn metal layer is sandwiched between adjacent graphene sheets. This compound undergoes a superconducting transition at Tc=3.75 K at H=0. The H–T diagram of Sn-MG is similar to that of a quasi-2D superconductors. The phase boundaries of vortex liquid, vortex glass, and vortex lattice phase merge into a multicritical point located at T ∗ =3.4 K and H ∗ =40 Oe. There are two irreversibility lines denoted by Hgl (de Almeida–Thouless type) and Hgl′ (Gabay–Toulouse type), intersecting at T0′=2.5 K and H0′=160 Oe. The nature of slow dynamic and nonlinearity of the vortex glass phase is studied.

Superconductivity and magnetic short-range order in the system with a Pd sheet sandwiched between graphene sheets

Pd-metal graphite (Pd-MG) has a layered structure, where each Pd sheet is sandwiched between adjacent graphene sheets. The DC magnetization and AC magnetic susceptibility of Pd-MG have been measured using a SQUID magnetometer. Pd-MG undergoes a superconducting transition at Tc (= 3.63 ± 0.04 K). The superconductivity occurs in the Pd sheets. The irreversibility between χZFC and χFC occurs well above Tc. The susceptibility χFC obeys a Curie–Weiss behaviour with a negative Curie–Weiss temperature (). The growth of magnetic order is limited by the disordered nature of nanographites, forming magnetic short-range order at low temperature in the graphene sheets.

Scaling form of zero-field-cooled and field-cooled susceptibility in superparamagnet

Abstract The scaling form of the normalized ZFC and FC susceptibility of superparamagnets (SPMs) is presented as a function of the normalized temperature y ( = k B T / K u 〈 V 〉 ) , normalized magnetic field h (= H / H K ), and the width σ of the log-normal distribution of the volumes of nanoparticles, based on the superparamagnetic blocking model with no interaction between the nanoparticles. Here 〈 V 〉 is the average volume, K u is the anisotropy energy, and H K is the anisotropy field. Main features of the experimental results reported in many SPMs can be well explained in terms of the present model. The normalized FC susceptibility monotonically increases as the normalized temperature y decreases. The normalized ZFC susceptibility exhibits a peak at the normalized blocking temperature y b ( = k B T b / K u 〈 V 〉 ) , forming the y b vs h diagram. For large σ ( σ > 0.4 ) , y b starts to increase with increasing h , showing a peak at h = h b , and decreases with further increasing h . The maximum of y b at h = h b is due to the nonlinearity of the Langevin function. For small σ , y b monotonically decreases with increasing h . The derivative of the normalized FC magnetization with respect to h shows a peak at h =0 for small y . This is closely related to the pinched form of M FC vs H curve around H =0 observed in SPMs.

Magnetic-field-induced superconductor-metal-insulator transitions in bismuth metal graphite

Bismuth metal graphite (MG) has a unique layered structure where Bi nanoparticles are encapsulated between adjacent sheets of nanographites. The superconductivity below T c (= 2.48 K) is due to Bi nanoparticles. The Curie-like susceptibility below 30 K is due to conduction electrons localized near zigzag edges of nanographites. A magnetic-field-induced transition from metallic to semiconductorlike phase is observed in the in-plane resistivity ρ a around H c (25 kOe) for both H ⊥ c and H‖‖c (c: c axis). A negative magnetoresistance in ρ a for H ⊥ c (0 40 kOe) suggest the occurrence of a two-dimensional weak-localization effect.

a- and c-axis resistivity and magnetoresistance in graphite intercalation compounds

The a-axis electrical resistivity and the transverse magnetoresistance (aT-MR ) of stage-2 to 6 graphite intercalation compounds (GICs) have been measured in the temperature (T) range between 4.2 and 300 K and magnetic field (H) range between 0 and 7 kOe. The data are analysed together with the results of c-axis resistivity and the longitudinal magnetoresistance (cL-MR ) reported in our previous work. For stage-2 to 5 GICs shows a metallic-like T dependence and exhibits no logarithmic behaviour, while shows a metallic-like behaviour for low stage (2), a logarithmic behaviour for the intermediate stages (3, 4) and a semiconductor-like behaviour for high stages (5, 6). For all stages the sign of aT-MR is positive, while the sign of cL-MR is negative for the intermediate stages (3-5) and positive for low stages in low T and weak H. The resistivity is formed of a series connection of G-I-G (G: graphite layer, I: intercalate layer) and G-G resistivity, while is formed of a parallel connection of each layer contribution. The behaviour difference between and is discussed in the light of the role of the interior G layer forming a bottleneck to the c-axis conduction. The logarithmic behaviour and negative magnetoresistance in arise from the two-dimensional weak localization occurring in these interior G layers.

Effect of random disorder and spin frustration on the reentrant spin-glass and ferromagnetic phases in the stage-2 Cu 0.93 Co 0.07 Cl 2 graphite intercalation compound near the multicritical point

Stage-2 Cu

Memory and aging effect in hierarchical spin orderings of the stage-2 Co Cl 2 graphite intercalation compound

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Transport properties of stage-1 magnetic random-mixture graphite intercalation compounds

Co

Dimensional Crossover and Angular Dependent Magnetoresistance of Magnetic Graphite Intercalation Compounds; MCl 2 GIC's (M=Cu and Co)

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