Senni Motomura

Systematic study of magnetic properties in Zn-based Tsai-type icosahedral quasicrystals and their approximant

We have investigated the magnetic properties of Zn-based Tsai-type icosahedral quasicrystals (i-QCs) and their approximants by measuring the field-and temperature-dependence of magnetization. The quasicrystals are formed by an addition of the third element M (M = Mg, Mn, Fe, Co, Ni, Cu, Pd, Ag, Pt or Au) to a Zn17Sc3 1/1 cubic approximant crystal. The remarkable feature of the Zn–M–Sc series is a variety of the additional M elements ranging from light metal Mg and 3d transition metals to noble metals. The experimental results obviously show that the i-QCs containing 3d transition metals (M = Mn, Fe, Co or Ni) have the local magnetic moment formation. We also confirmed appearance of Curie-Weiss paramagnetism for a Zn82Fe3Sc15 1/1 cubic approximant crystal. The present results indicate that the divalent Zn of major component in the present i-QCs and approximants may be favourable for the moment formation of iron group elements in contrast with the case of the trivalent Al-based i-QCs such as Al–Cu–Fe.

Formation and magnetic properties of p-type icosahedral quasicrystals in Zn–Fe–Sc–L (L = Ho, Er, Tm) alloys

Icosahedral quasicrystals containing heavy lanthanoids L, namely Ho, Er or Tm, have been discovered in the Zn77Fe7Sc16– x L x alloy systems. The solubility limit of the lanthanoid is approximately half of the Sc atoms. All these quasicrystals belong to p-type and are stable at approximately 973 K. The temperature dependence of the magnetic susceptibility of the Zn77Fe7Sc8Tm8 quasicrystal follows the Curie–Weiss law and exhibits spin-glass-like behaviour with a freezing temperature of 9 K. The Curie constants obtained by Curie–Weiss fit are larger than those calculated by the Lande g-factor of free Tm3+ ions based on Hunds rule, assuming all magnetization is caused by Tm atoms only. It is deduced that both Tm and Fe atoms exhibit magnetic moments. This is the first example of a stable icosahedral quasicrystal containing two types of magnetic atoms: Fe and the lanthanoids.

Magnetic Property of Stable Icosahedral Quasicrystal in Zn-Fe-Sc Alloy

We report the observation on the magnetic property of the stable Zn77Fe7Sc16 icosahedral quasicrystal discovered recently. As a result of measurements of magnetization, it became clear that the new Zn-based icosahedral quasicrystal has large local magnetic moments and exhibits spin glass behavior. The magnetization curves show Curie-like paramagnetism, where the magnetization M is 4.45 cgsemu/g at 5 K under 70 kOe. The temperature dependence of the magnetic susceptibility obeys the Curie-Weiss law between 76 and 300 K. On the assumption that all of the Fe atoms have the same magnitude of local magnetic moment, the effective number of Bohr magneton p of each Fe atom was estimated at 5.30 on average. Moreover, in the low-temperature region, the spin glasslike cusp of the magnetic susceptibility was observed with a freezing temperature Tf = 7.2 K.

Magnetic property of a Zn-Mg-Sc icosahedral quasicrystal

We have investigated the magnetism of a new Zn 80 Mg 5 Sc 15 P-type icosahedral quasicrystal and a Zn 85.5 Sc 14.5 cubic phase, which is interpreted to be a 1/1 approximant of the new icosahedral quasicrystal, in the temperature region between 2 and 700 K. The magnetic susceptibility of the Zn 80 Mg 5 Sc 15 icosahedral quasicrystal shows an increase from -1.3×10 -7 to -0.8×10 -7 cgsemu/g with a rise in temperature from 90 to 700 K. The Zn 85.5 Sc 14.5 cubic phase shows also a rise from -1.8×10 -7 to -1.0×10 -7 cgsemu/g between 120 and 700 K. The increase in the susceptibility with a rise in temperature is accounted for by a temperature dependence of the Pauli paramagnetism. The experimental results strongly suggest a pseudogap in the electronic density of states at Fermi energy for the Zn 80 Mg 5 Sc 15 quasicrystal and the Zn 85.5 Sc 14.5 approximant, which has been observed in various stable icosahedral quasicrystals.

Ising Spin Orders Conforming to Local Matching Rule and Long-Range Regularity of Interactions in Penrose Lattice

A simple arithmetic rule is proposed to correlate the matching rule in Penrose lattice with long-range Ising spin orders with the aim of clarifying the energetic mechanism of the orders under Ruderman–Kittel–Kasuya–Yoshida-like (RKKY) alternating interactions. Three different types of antiferromagnetic orders were found to be compatible with the rule. The orders showed sharp magnetic diffraction spots with the same peak widths as the ordinary lattice diffraction, which were consistent with the long-range orders enforced by the matching rule. The three types of the orders were most adequately interpreted as the orders in the occupation domain in the phason space. The RKKY interactions resulted in two of the orders in simulated annealing calculations. The results indicate the importance in the energetic mechanism of the consistency of the connectivity of the interaction signs inherent in the quasiperiodic structure.

Ising spin orders and magnetic interactions analyzed in phason space in a 2-dimensional Penrose lattice

Simulated annealing calculations were performed on a Penrose lattice with the aim of clarifying the relation between the interaction connections and the magnetic orders in the phason space. Alternating signs were assumed in the magnetic interactions up to the second shortest distances between spins. Two different types of long-range antiferromagnetic orders were found for two cases with reversed sign of the interactions. The two types of order were most adequately interpreted as the orders of subdivisions in the occupation domain in the phason space. Reasonable interpretations of the mechanism of the subdivisions are given on the basis of the physical interactions projected to the phason space.

Simulation study on antiferromagnetic order of Ising spins in a Zn-Mg-Ho model structure

A long-range antiferromagnetic order was studied on Ising spins in a Zn–Mg–Ho model structure for Ruderman–Kittel–Kasuya–Yosida (RKKY)-like alternating magnetic interaction in simulated annealing calculations. The order showed sharp magnetic diffraction peaks, with similar widths as ordinary lattice diffraction, but diminished intensity of the central peak. This indicated a long-range antiferromagnetic order. The order was most suitably interpreted as a separation of the occupation domain in the phason space. The energetic mechanism of the order was qualitatively analysed in magnetic interaction connections in the phason space.

Magnetic properties of F2M-type Al-Pd-Mn quasicrystals

Abstract We measured temperature dependence of the susceptibility of the F2M-type Al–Pd–Mn quasicrystals in the range of temperature T between 2 and 600 K. In the range 2 K T T T

Electrical Properties of a Stable Icosahedral Quasicrystal Zn-Fe-Sc

The electrical resistivity of a recently discovered stable icosahedral quasicrystal Zn 77 Fe 7 Sc 16 was found to have a T 1/2 dependence in low temperature region between 2 and 16 K, while it increased gradually by 6.8% with the decrease in temperature from 270 to 2 K. The increase is considered to arise from the weak localization of conduction electrons. Negative magnetoresistance was found below 32 K. The T 1/2 dependence of the resistivity and the negative magnetoresistance are interpreted on the basis of the short range magnetic order inferred from the spin-glass behavior.