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Body-centered-cubic (bcc) Fe50Co50 material is reported to show a high bulk spin scattering coefficient on current perpendicular to plane–giant magneto-resistance (CPP–GMR) system. But the origin of that phenomenon does not make sure yet. We prepared artificially alternate monatomic layered (AML) [Fe/Co] 41 MLs epitaxial films (Ts: 75, 250 °C) by monatomic deposition method and investigated the topology of AML [Fe/Co]n epitaxial films on MgO substrate with different orientation (001), (011) by the scanning tunnel microscopy (STM) and reflection high energy electron diffraction (RHEED), which we could confirm Frank–van der Merwe (FM) growth mode for AML [Fe/Co]n on MgO(001) and Volmer–Weber (VW) growth mode for that on Mg(011). The roughness of surface, Ra (0.20 nm) of AML [Fe/Co] 41 MLs epitaxial film grown at 75 °C on MgO(001) is smaller than that (0.46 nm) of AML [Fe/Co] grown at 250 °C on MgO(001), which has the large terraces of over 50 nm (Ra: 0.17 nm), even though there are some valleys between large terraces. Moreover we confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n (Ra: 0.18 nm) and Fe50Co50 alloy epitaxial film on Au electrode by RHEED before confirming the characteristics of CPP–GMR devices.

We investigated perpendicular exchange bias switching by a magnetoelectric field cooling process in a Pt-spacer-inserted Cr2O3/Co exchange-coupled system exhibiting small Cr2O3 magnetization. Although higher magnetoelectric switching energies with decreasing Cr2O3 thickness due to the exchange bias were reported in Cr2O3/Co all-thin-film systems, in this study, we demonstrated low-energy switching in a magnetoelectric field cool process regardless of the exchange-bias magnitude; we balanced the exchange-bias energy with the Zeeman energy associated with finite magnetization in Cr2O3. We proposed a guideline for realizing low-energy switching in thin Cr2O3 samples.

A multiple phase change structure with Sb79Te21 for switching and Ge1Cu2Te3 for memory was fabricated and evaluated for cell operation. It was confirmed that Sb79Te21 with smaller contact diameter is successfully operated or used as a switching device with selective current pulses. In addition, it was estimated that this structure provides acceptable on–off ratio and leakage current by structural consideration. From these results, we consider that the structure with multiple phase change materials is suitable as a new device with both switching and memory functions, which gives higher scalability in three-dimensional array architecture by adopting no additional selective devices, such as transistors and diodes. Therefore, we expect that this structure can be one of the candidates for the scalable phase change random access memory (PCRAM).

The spin polarization (P) of alternate monatomic layered (AML) epitaxial [Fe/Co] n superlattices grown on MgO(001) substrates by electron beam (EB) evaporation has been measured by the point contact Andreev reflection (PCAR) method. The intrinsic transport P of 0.60 was obtained for the AML epitaxial [Fe/Co] n superlattice grown at 75 °C, which is comparable to that of half-metallic Heusler alloys measured by PCAR. The AML epitaxial [Fe/Co] n superlattices on MgO(001), which are expected to possess the B2 ordered structure, show the highest spin polarization of metallic Fe–Co alloy films.

A magnetic nanocontact spin valve (NCSV) was fabricated by inserting a TaO x nano-oxide layer (NOL) as the spacer layer. Current-perpendicular-to-film-plane (CPP) measurements revealed that the SV had a positive magnetoresistance (MR) ratio. When a high bias voltage was applied to the SV, the fine structure of the NOL changed i.e., the resistance and MR ratio of the device changed irreversibly. The change in device characteristics is attributed to a proportional change in the number of nonmagnetoresistive and magnetoresistive conductive channels in the SV upon high bias voltage application. The decrease in MR ratio accompanied the disappearance of the magnetic nanocontact, suggesting that the positive MR effect was partially due to the presence of magnetic nanocontacts.

The Co substitution effect on the magnetostrictive properties of DyFe2 has been investigated using magnetic measurement. The specific saturation magnetization σs of the Dy(Fe1-x Cox)2 compounds firstly decreases with x and then increases. The magnetostriction constant λt of these compounds increases with x monotonically. These phenomena are been discussed.

The specific heat and magnetic susceptibility have been measured for Er3Co. The magnetic susceptibility obeys the Curie-Weiss law in the temperature range of 100-300 K with the effective moment µeff=9.52µB. A large magnetic specific heat above the Curie temperature of 13 K was found, which is interpreted in terms of the point-charge model. It is revealed that the crystal field and exchange field are of the same order of magnitude and that the electronic thermal excitations contribute to the magnetic specific heat, resulting in a broad Schottky-type contribution. Moreover, magnetocrystalline anisotropy gives rise to the noncollinear spin structure.

Specific heat measurement was performed in the temperature range from 800 mK to 62 K on the regenerator material Er3Ni which is an antiferromagnet with a Néel temperature of 6.1 K and possesses a large volumetric heat capacity even at temperatures aboveTN. The magnetic contribution to the specific heat has been carefully divided into two parts, one of which is caused by entropy change due to the magnetic ordering and the other a contribution from higher energy level states (Schottky anomaly). The energy levels of the 4f electrons for Er3+were calculated using the point-charge model, and compared with the experimental data. The entropy change of the Schottky anomaly is large compared with that of magnetic ordering and important for the regenerator material.

Er3Ni specific heat in 0, 1, 3, and 4.3 T magnetic fields was measured. The specific heat curves for 0 T and 1 T have a single peak due to magnetic phase transition, but those for 3 T and 4.3 T have no peak. Er3Ni specific heat decreases with increasing magnetic field around its ordering temperature, but increases in the higher-temperature region. Using the measured specific heat data, regenerator efficiency and cooling power were calculated to estimate the specific heat reduction influence due to a magnetic field on the Er3Ni regenerator performance. The results show that efficiency and cooling power in the practical leaking magnetic field are almost the same as those in 0 T.

A complex magnetic material for use in the Ericsson magnetic refrigerator was investigated. In order to refrigerate effectively in the high temperature range above 10K, it is necessary to utilize the Ericsson cycle that includes two kinds of iso-magnetic field process, because lattice entropy for a magnetic refrigerant amounts to the same order of magnitude as that for magnetic entropy. Therefore in the Ericsson magnetic refrigerant, magnetic entropy change ΔSM is required to be constant in the refrigeration range. This property, however, cannot be satisfied by usual ferromagnetic material. In this paper, the complex RAl2 magnetic mixture (where R denotes heavy rare earth atoms) in grain size scale is prepared by shock compression method. Magnetic entropy changes are determined from the specific heat measurement. This magnetic mixture has high density, which is composed of several RAl2 compounds with different Curie temperatures, where each RAl2 is surrounded by gold. From these experimental results, it is concluded that the complex magnetic mixture with gold, such as (ErAl2)0.3 (HoAl2)0.2(Dy0.5Ho0.5Al2)0.5, shows an almost temperature independent magnetic entropy change ΔSM in some temperature range, which is suitable for the Ericsson cycle, satisfying the Carnot principle.

In the temperature range above ∼20 K, the Ericsson magnetic refrigeration cycle has to be adopted instead of the Carnot cycle, because the lattice entropy becomes no longer negligible as compared with the magnetic entropy. Moreover, in this range since the thermal agitation energy ∼kT of spin also increases, the ferromagnetic materials have to be used for the refrigerant to obtain large entropy change enough to refrigerate. However, temperature variation of the magnetic entropy change of ferromagnetic material is not suitable for the Ericsson cycle. In the present paper we will give the answers to the following questions; (1) what kinds of ferromagnets must be used for the refrigerant? (2) what kind of method to compose the refrigerant using those ferromagnets is promising?