Magneto-optical Measurements using a Hybrid Magnet(Part II. Several Instruments and Techniques Developed in HFLSM)

Magneto-absorption spectra were obtained in the fields up to 23 T by means of a hybrid magnet at Tohoku University. The absorption was obtained by measuring the intensity of transmitted light through the sample. Optical fiber systems were utilized for the light transmission, which enabled rapid assembly of the light pass within a restricted machine time. The spectra were taken in the wavelength region of about 300 to 2000 nm. The monochromator was fully remote controlled from outside of the magnet room by a computer

Response of a Living Body to 8-Tesla Magnetic Field(Crystal Growth, Chemical Reaction and Biology)

A study was made to investigate body function in high magnetic field of 8-tesla. In order to avoid magnetic-field effect on the measuring system, long distance was placed between a experimental animal and the measuring system. Changes in contractility of the heart were measured from frogs. Heart and respiratory rates were recorded from rabbits. Contractility of the heart was increased with increasing magnetic fields from 0 to 8 tesla in frogs. Heart and respiratory rates were decreased with increasing magnetic fields from 0 to 8 tesla

Magneto-Absorption Spectra of One-Dimensional Ising Antiferromagnets in High Magnetic Fields(Magnetooptics)

We have performed magneto-absorption spectra measurements of the quasi-one-dimensional antiferromagnet RbFeCl_3.2H_2O with a hybrid magnet installed at High Field Laboratory for Superconducting Materials in Tohoku University

Antiferromagnetic transition in ternary rare-earth metal silicide Er5Ir4Si10 single crystal

金沢大学理工研究域数物科学系We have precisely investigated the antiferromagnetic phase transition in the ternary rare-earth metal silicide Er5Ir4Si10 single crystal by performing the high-resolution measurement of the low-temperature specific heat under zero-magnetic field and the AC magnetization. In the temperature dependence of important physical quantities associated with the antiferromagnetic phase transition, we have observed anomalies associated with the antiferromagnetic long-range ordering at Neel temperature TN. We have confirmed that TN is 3.5 K. In addition, we have first observed two surprising results. Firstly, a shoulder was observed in the vicinity of 2 K in addition to the sharp peak at TN corresponding to the antiferromagnetic long-range ordering in the high-resolution measurement of the low-temperature specific heat. Secondly, the anomaly of the AC magnetization at TN depends on the magnetic field direction. Though we have clearly observed the anomaly of the AC magnetization associated with the antiferromagnetic phase transition at TN when the AC magnetic field direction is parallel to the c-axis, we have observed no anomaly of the AC magnetization at TN when the AC magnetic field orientation is perpendicular to the c-axis. These results clarify that our Er5Ir4Si10 single crystal is a quasi-two-dimensional antiferromagnet and then has no magnetic structure of the Er3+ local moments. However, we have observed a peak of the AC magnetization at around 2 K when the AC magnetic field is perpendicular to the c-axis. This temperature corresponds to that at which a shoulder is observed in the high-resolution measurement of the low-temperature specific heat. Furthermore, we have observed no frequency dependence of the AC magnetization which is ordinarily observed in the spin glass state. This result means that there is no disorder in our Er5Ir4Si10 single crystal because the crystal structure of Er5Ir4Si10 has the tetragonal crystal structure in which the octagons of Er3+ ions are stacked. In addition, both the tetragons and the octagons of Er3+ local moments have no magnetic frustration. At last, we can conclude that both the shoulder of the low-temperature specific heat in the vicinity of 2 K and the peak of the AC magnetization at around 2 K, which is only observed when the AC magnetic field direction is perpendicular to the c-axis, correspond to the crystalline electric field effect in the plane which is perpendicular to the c-axis of the tetragonal crystal structure. © 2008 Elsevier B.V. All rights reserved

Direct observation of remarkable crystalline-electric-field effect in quasi-two-dimensional antiferromagnet Er5Ir4Si10 single crystal by low-temperature specific heat

金沢大学理工研究域数物科学系We have intensively investigated the antiferromagnetic phase transition in the ternary rare-earth metal silicide Er5Ir4Si10 single crystal by performing the high-resolution measurement of the low-temperature specific heat under zero-magnetic field and the AC magnetization. In the temperature dependence of important physical quantities associated with the antiferromagnetic phase transition, we have observed anomalies with the antiferromagnetic long-range ordering at Neel temperature T N. We have confirmed that T N is 3.5 K. In addition, we have first observed two surprising results. Firstly, a shoulder was observed in the vicinity of 2 K in addition to the sharp peak at T N corresponding to the antiferromagnetic phase transition in the high-resolution measurement of the low-temperature specific heat. Secondly, the anomaly of the AC magnetization at T N depends to the magnetic field direction. We have clearly observed the anomaly of the AC magnetization at T N when the AC magnetic field orientation is parallel to the c-axis, whereas we have observed no anomaly of the AC magnetization at T N when the AC magnetic field orientation is perpendicular to the c-axis. These results clarify that our Er5Ir4Si10 single crystal is a quasi-two-dimensional antiferromagnet and has no three-dimensional magnetic structure of the Er3+ local moments. However, we have observed a peak of the AC magnetization around 2 K when the AC magnetic field orientation is perpendicular to the c-axis. This temperature corresponds to that at which a shoulder is observed in the measurement of the low-temperature specific heat. Furthermore, we have observed no frequency dependence of the AC magnetization which is ordinarily observed in the spin glass state. This result means that there is no disorder in our Er5Ir4Si10 single crystal because the crystal structure of Er5Ir4Si10 has the tetragonal crystal structure in which the octagons of Er3+ ions are stacked. In addition, both tetragons and octagons of Er3+ local moments have no magnetic frustration. At last we can conclude that both the shoulder of the low-temperature specific heat in the vicinity of 2 K and the peak of the AC magnetization around 2 K, which is only observed when the AC magnetic field orientation is perpendicular to the c-axis, correspond to the crystalline-electric-effect in the plane which is perpendicular to the c-axis of the tetragonal crystal structure. © 2008 Elsevier B.V. All rights reserved

High-Magnetic-Field Studies of the Kondo Semiconductor CeNiSn(Transport and Fermiology)

The Kondo-lattice compound CeNiSn behaves as a narrow-gap semiconductor at low temperatures below 7 K. The effect of magnetic field on the gapped state of this compound has been studied by the measurements of magnetization, magnetoresistance and specific heat on a single-crystalline sample. A weak metamagnetic transition and very large negative magnetoresiostance are observed only when a magnetic field higher than 13 T is applied along the α axis of the orthorhombic structure. These results show that the pseudogap is suppressed anisotropically by the magnetic field. The collapse of the gap is accompanied with the evolution of a polarized heavy-fermion state

Measurement of de Haas-van Alphen Effect with Hybrid Magnet(Transport and Fermiology)

An apparatus to measure the de Haas-van Alphen effect in steady high magnetic field has been constructed by using hybrid magnets at Tohoku University. Fermi surfaces were investigated on cuprate high-temperature superconductor and rare earth antimonide. The spectral analyses were performed by using the maximum entropy method as well as the Fourier transformation. In magnetically oriented YBa_2Cu_3O_ and Tl_2Ba_2CuO_ powder , the spectral density shows a peak at 456 T and 400 T, respectively. A slight change of extremal cross-section was found in PrSb above 15 T

Valence and Na content dependences of superconductivity in NaxCoO2.yH2O

Various samples of sodium cobalt oxyhydrate with relatively large amounts of Na$^{+}$ ions were synthesized by a modified soft-chemical process in which a NaOH aqueous solution was added in the final step of the procedure. From these samples, a superconducting phase diagram was determined for a section of a cobalt valence of $\sim$+3.48, which was compared with a previously obtained one of $\sim$+3.40. The superconductivity was significantly affected by the isovalent exchanger of Na$^{+}$ and H$_{3}$O$^{+}$, rather than by variation of Co valence, suggesting the presence of multiple kinds of Fermi surface. Furthermore, the high-field magnetic susceptibility measurements for one sample up to 30 T indicated an upper critical field much higher than the Pauli limit supporting the validity of the spin-triplet pairing mechanism.Comment: 4 figures and 1 tabl

High Field Magnetooptics of Diluted Magnetic Semiconductors(Magnetooptics)

Absorption and luminescence spectra of Cd_Mn_xSe (x=0.10 and 0.38) and reflectance spectra of Cd_Co_xSe (x=0.012) were investigated in high magnetic fields up to 25 T by a hybrid magnet and a magnetospectrometer with an optical fiber system