Magnetic Structures and Magneto-volume Effects in Mn3Cu1-xGexN
- PDF / 416,628 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 68 Downloads / 159 Views
1027-D04-02
Magnetic Structures and Magneto-volume Effects in Mn3Cu1-xGexN Satoshi Iikubo1, Katsuaki Kodama1, Koshi Takenaka2,3,4, Hidenori Takagi2,3, and Shinichi Shamoto1 1 Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki, Japan 2 The Institute of Physical and Chemical Research, RIKEN, Wako, Saitama, Japan 3 CREST, Japan Science and Technology Agency, Kawaguchi, Saitama, Japan 4 Department of Crystalline Materials Science, Nagoya University Furo-cho, Chikusa-ku, Nagoya, Japan ABSTRACT Magnetic structures in an antiperovskite system, Mn3Cu1-xGexN, with a large magneto-volume effect above x =0.15 have been studied by neutron powder diffraction measurement. The present neutron study revealed that not only a cubic crystal structure but also a Γ5g antiferromagnetic spin structure are key ingredients of the large magneto-volume effect in this itinerant electron system. INTRODUCTION Recently, a giant negative thermal expansion coefficient in Mn3Cu1-xGexN was reported by Takenaka and Takagi [1-3]. Thermal expansion ∆L/L gradually decreases with increasing temperature (T) over a broad range of 270 < T < 350 K at x~0.5. The large negative coefficient of linear thermal expansion α is about -2 × 10-5/K, one of the largest negative values among all NTE materials. The negative thermal expansion (NTE) materials have already been used in a wide area of technical applications in which it is desperately needed to control the thermal expansion [4,5]. An important mechanism of NTE is the magneto-volume effect (MVE). With increasing T, the volume can be constricted gradually by changing the amplitude of the magnetic moment. The MVE has been an important problem closely connected to the basics of itinerant electron magnetism [6-9]. However, there is no simple relationship between the magnitude of the MVE and the magnetization in this system. For Mn3CuN, the volume change is negligibly small at the ferromagnetic transition temperature TC=143 K, accompanied by a cubic-to-tetragonal structural phase transition. On the other hand, at x=0.15, linear thermal expansion ∆L/L rapidly increases at TC~100 K with decreasing T [1-3]. The variation in the magnetization M with Ge doping is shown in Figure 1. It smoothly changes from the ferromagnetic to the antiferromagnetic state. It must be noted that the T-dependence of the magnetic susceptibility of Mn3Cu0.85Ge0.15N is qualitatively identical to that of Mn3CuN. Therefore, we suggest that other effects are more relevant to the large MVE of this system. In order to understand the Ge-doping effect on the magnetic properties and MVE in Mn3Cu1-xGexN, we have studied the magnetic structure using neutron powder diffraction.
Fig. 1: T-dependence of magnetization M of Mn3Cu1-xGexN with x=0, 0.15, 0.2, and 0.5. EXPERIMENT Polycrystalline samples of Mn3Cu1-xGexN with x=0, 0.15, 0.2, and 0.5 were prepared by the solid-state reaction [1-3]. The experiments were performed on the high-resolution powder diffractometer HRPD λ=1.8233 Å and the triple axis spectrometer TAS-2 λ=2.3590
Data Loading...
