Difference in elastic properties of CrB 2 determined by microscopic and macroscopic measurements
- PDF / 3,466,678 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 54 Downloads / 169 Views
Difference in elastic properties of CrB2 determined by microscopic and macroscopic measurements Katsushi Tanaka1, Satoshi Tsutsui2, Norihiko L. Okamoto3, Haruyuki Inui3 and Alfred Q.R. Baron2,4 1 Department of Mechanics, Kobe University, Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan. 2 Japan Synchrotron Radiation Research Institute, SPring-8, Sayo-cho, Sayo-gun, Hyogo 6795198 Japan. 3 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 6068501, Japan. 4 RIKEN, SPring-8, Sayo-cho, Sayo-gun, Hyogo 679-5143, Japan ABSTRACT CrB2 possess the hexagonal AlB2 structure which belongs to the spacegroup of P6/mmm. The compound exhibits para- to antiferro-magnetic transition at about 88 K. By using a macroscopic measurement technique, that is, a conventional resonant ultrasound spectroscopy (RUS) with a millimeter size mono-crystal, significant elastic anomalies have been observed just above the magnetic transition temperature. On the other hand, elastic constants determined by a microscopic measurement technique, that is, an inelastic X-ray scattering method (BL35XU of SPring-8, Japan) do not show any elastic anomalies at around the transition temperature. In order to explain the discrepancy, we have introduced a kind of so called ΔE effect resulting from a multidomain structure. If crystal lattice is slightly deformed by a spontaneous magnetostriction in the antiferromagnetic state, the symmetry of crystal lattice is lowered from hexagonal to monoclinic when the symmetry of magnetic structure is taken into account. By the lowering of the symmetry, the crystal consists of six magnetic domains in the antiferro magnetic state. If magnetic domain boundaries move in response to externally applied stresses, the mechanical deformation is absorbed by nonelastic deformations induced by the movement of magnetic domain boundaries. This multidomain model well explains the experimental results obtained by both microscopic (X-ray) and macroscopic (ultrasound) measurements. The microscopic measurement technique is useful to obtain the true elastic properties of crystal lattice without effects coming from a multidomain structure. INTRODUCTION Transition metal diborides have several attractive physical and chemical properties such as high melting temperature, high elastic moduli and high electric conductivity. The most known transition metal diborides posses the hexagonal AlB2 structure which belongs to the spacegroup of P6/mmm [1]. Since considerable interests in many technological applications have been accumulated to the compounds, physical properties of transition metal diborides have been reported frequently. We also have reported elastic constants and thermal expansion of monocrystalline TiB2, CrB2 and ZrB2 determined in the temperature range from room temperature to 1373 K [2]. Among of the compounds, chromium diboride exhibits a magnetic transition between para- and antiferro- magnetic states with TN = 88 K [3]. The magnetic structure in the ordered
state has firstly reported by Funahashi et al. as an un
Data Loading...
