Kenichi Ishimoto

Magnetic structure of UTGe (T: Ni, Pd, Pt) single crystals

Abstract The magnetic structures of UTGe (T: Ni, Pd, Pt) have been determined by neutron diffraction measurements on single crystalline samples. UNiGe has a simple collinear antiferromagnetic structure below 42 K. UPdGe has a longitudinal sinusoidal structure along the c-axis between 28 and 50 K, while it transforms to a ferromagnet at 28 K. UPtGe has a cycloidal structure with the Q-vector parallel to the b-axis below 50 K. In all these magnetic structures, the magnetic moments are almost in the bc-plane and couple ferromagnetically with each other along the a-axis.

Magnetic and transport properties of UTGe (T: Ni, Pd and Pt)

The results of the magnetization, neutron diffraction, specific heat and electrical resistivity measurements are reported on the single crystalline samples of UTGe (T: Ni, Pd and Pt). UNiGe and UPtGe show the antiferromagnetic transitions at 42 and 50 K, respectively. UPdGe undergoes successive magnetic transitions; an antiferromagnetic transition at 50 K and a ferromagnetic one at 28 K.

Electrical resistivity of UTGe (T: Ni, Pd, Pt) single crystals

Abstract The electrical resistivity of three single crystals of UTGe (T: Ni, Pd, Pt) have been measured in a magnetic field up to 60 kOe. In all samples, Kondo-like behavior was observed between 100 and 300 K in zero field. A large reduction of the resistivity accompanied by a metamagnetic transition in UPdGe was observed for H‖b- or c-axis. It is suggested that a magnetic superzone is formed in the antiferromagnetic state with long-period structure in UPdGe and UPtGe.

Anomalous region in the magnetic phase diagram of (Fe, Co)Si

The temperature and magnetic field dependence of the magnetic properties of helimagnet Fe 0.8 Co 0.2 Si is studied by magnetic measurement and small angle neutron diffraction. It is shown that Fe 0.8 Co o.2 Si exhibits a magnetic phase transition from conical to a new modulated spin state, phase A, just below T N in the field range of 0.3 kOe H

Small-angle neutron diffraction from the helical magnet Fe0.8Co0.2Si

The preferred direction of the helical axis in Fe0.8Co0.2Si has been studied by small-angle neutron diffraction. In the virgin state, the helical axis points along all directions of the crystal. The analysis of the shape of the Bragg scattering indicates that the propagation vector tends to lie along the 〈0 0 1〉 axis in Fe0.8Co0.2Si.

Magnetization of UTGe(T:Ni, Pd, Pt) single crystals in high magnetic fields

Abstract The high-field magnetization of UTGe (T:Ni, Pd, Pt) single crystals were measured at 4.2 K by an extraction method using the Tohoku hybrid magnet. A large anisotropy and the metamagnetic transitions appear in the magnetization process for all of the three samples. The high field susceptibility is considerably large in UNiGe and UPdGe.

Long Periodic Magnetic Structure in CeB2C2

In this paper, we provide information on the magnetic structure in tetragonal CeB2C2, which is isostructural with the antiferroquadrupolar (AFQ) ordering compound DyB2C2, and discuss peculiarities of CeB2C2 among the RB2C2 (R = rare earth) system. Some of the RB2C2 compounds, which have the tetragonal LaB2C2 type structure, 1) exhibit characteristic AFQ orderings with antiferromagnetic (AFM) orderings. For instance, DyB2C2 undergoes an AFQ ordering at TQ 1⁄4 24:7K, which is nearly ten times higher than those in other AFQ ordering compounds, and an AFM ordering at TN 1⁄4 15:3K with a complicated magnetic structure. Thus, the RB2C2 compounds are attracted our interests by characteristic AFQ and AFM orderings with tetragonal symmetry. Of this system, HoB2C2, TbB2C2 and ErB2C2 have long periodic magnetic ordering states with close periodicity in the c-plane. Moreover, in the long periodic states of HoB2C2 and TbB2C2, which show characteristic AFQ orderings, similar and anomalous magnetic diffuse scattering which can not be understood by only magnetic correlations was observed in the region surrounded by the satellite peaks by neutron diffraction. The close periodicity and the similar anomalous scattering in spite of the different 4f states implies that the long periodic states originate in some common mechanism in RB2C2; therefore, the long periodic states is worthy of clarifying in details to understand properties in RB2C2. Our preliminary neutron powder diffraction experiments suggest that CeB2C2 also has a long periodic magnetic ordering state; however, the periodicity and magnetic structure are not determined yet because of weakness of magnetic scattering intensity. To obtain more accurate information on the magnetic structure in CeB2C2, we performed neutron diffraction experiments on a single crystalline sample of CeB2C2. CeB2C2 undergoes a magnetic ordering at TN 1⁄4 7:3K with a sharp peak in the temperature dependence of specific heat CpðTÞ, and a successive transition at Tt 1⁄4 6:5K with a broad hump in CpðTÞ. The temperature dependence of magnetic susceptibility ðTÞ also shows an peak at TN when magnetic field is applied along the a and [110] directions without anisotropy in the c-plane, while no obvious anomaly was observed at Tt in ðTÞ. Since the c-plane is the magnetic easy plane, the magnetic moments lie in the c-plane. The single crystal for the neutron diffraction experiments was grown by the Czochralski method with a tri-arc furnace from the mixtures of 99.9% pure Ce, 99.5% pure B and 99.999% pure C. Natural B was enriched by B so that we avoided the strong absorption effect by B in natural B. The neutron diffraction experiments were performed on the Kinken (Institute for Materials Research) neutron diffractometer KSD installed at the reactor, JRR-3M, in Japan Atomic Energy Research Institute; the wave length was 1⁄4 1:52 A, and the collimation condition was 120-opensample-300. Figure 1 shows a Bragg peak found in this work at T 1⁄4 2:2K below Tt 1⁄4 6:5K. The magnetic origin is evident because the peak disappears above TN. From Gaussian fitting procedure, the centre of the peak was determined as (0.161(2), 0.161(2), 0.100(2)). The result indicates that the magnetic structure of CeB2C2 at 2.2K is a long periodic one with a propagation vector of k 1⁄4 ð ; ; 0Þ, where 1⁄4 0:161ð2Þ 1=6, 0 1⁄4 0:100ð2Þ 1=10. In fact, all the Bragg peaks observed at T 1⁄4 2:2K can be indexed with this propagation vector; therefore, the magnetic structure below Tt is represented with the single propagation vector, k 1⁄4 ð ; ; 0Þ. We can not discuss the correlation length of the magnetic ordering, because of the bad mosaicity of the sample. Figure 2 shows the temperature dependence of the integrated intensity of the peak in Fig. 1 with careful 150

Multi-magnetic-mode in (Cr1−xMnx)2As

Abstract Concentration and temperature dependence of the magnetic structure is investigated by means of powder neutron diffraction on the compounds of (Cr 1− x Mn x ) 2 As system for the concentration range of 0≤ x ≤0.5. There are two cation sites, A and B, in this crystal structure, and Mn atoms preferred to occupy site-B. The magnetic structure realized in this system is found to be such a special one that isotropic exchange interactions cancel out between site-A and B cations for the whole range of the present investigation. The site-A and B cations behave independently with each other, as the former aligns at T t and the latter at T N .

Magnetic phase transitions in UNi1−xPdxGe and UPd1−yPtyGe

Abstract Magnetizations were measured for both UNi 1− x Pd x Ge ( x = 0.0, 0.25, 0.5, 0.75) and UPd 1− y Pt y Ge( y = 0.0, 0.25, 0.5,0.75, 1.0) systems. UNi 1−x Pd x Ge shows a sinusoidal magnetic transition with T N ≃ 55 K followed by fe rromagnetic trans-formation below 40 K. Pd rich UPd 1−y Pt y Ge undergoes a ferromagnetic state with T c lower than 60 K, while the Pt rich UPd 1−y Pt y Ge compounds reveal cycloidal magnetic transition around 50 K. The mechanism by which various magnetic phases appear in UTGE (T = Ni, Pd, Pt) is considered to be due to competition of the exchange interactions in the bc -plane accompanied by a change in transition metals.

Magnetic Properties of Tetragonal Ce1-xLuxB2C2 (0 ≤x ≤0.31) Compounds

Specific heat, dc - and ac -magnetic susceptibility and magnetization measurements were performed on rare earth intermetallic compounds Ce 1- x Lu x B 2 C 2 (0 ≤ x ≤0.31) in order to elucidate the magnetic interaction in CeB 2 C 2 . In the process of the substitution of Ce by Lu in CeB 2 C 2 , the characteristics of magnetic transition change from a first-order transition to a second-order one. Furthermore, the spin-glass phase appears at Lu concentration x =0.31. We suppose that the ferromagnetic (FM) and antiferromagnetic (AFM) interactions compete and nearly cancel out each other in CeB 2 C 2 , and hence that a biquadratic interaction might cause the first-order magnetic transition at T N . The Lu substitution breaks the competition between AFM and FM interactions and brings forth randomness in interactions acting on each Ce moment. The typical spin-glass behavior of x =0.31 originates in this random distribution of magnetic interactions.