Large magnetic-field-induced strains in Ni-Mn-Ga alloys in rotating magnetic field

A single-crystal samples of near-stoichiometric Ni2MnGa alloys with large magnetic field induced strain (MSM effect) at room temperature have been investigated. It was found that there is a reversible reorientation of easy magnetization direction and magnetic domain structure under applied magnetic field. By means of x-ray Laue diffraction method and difractometric analysis it was ascertained that these phenomena are connected with the growth of martensitic twin variant with the short crystallographic axis (c-axis) directed along the applied magnetic field. Furthermore, by means magneto-optical investigations we have found the correlation between martensitic microstructure and magnetic domain structure. The field-induced reorientation of martensite was able to change the dimensional lengths of the samples more than 4.5 %

Crystal structure, magnetic properties, x-ray-photoemission-spectroscopy, and specific-heat measurements on Pr2BaO4 and PrBaO3.

We investigated Pr2BaO4 and PrBaO3 by several complementary experimental techniques. PrBaO3 crystallize in an orthorhombic structure. dc and ac susceptibility measurements exhibit irreversibility phenomena below TN=11.7 K and reveal the magnetic structure of PrBaO3, which consists of an antiferromagnetic ordering together with a small canting of the spins which produces the ferromagnetic component. Both magnetic and specific-heat studies show that TN is not affected by the applied magnetic field up to 9 T. Pr2BaO4 crystallizes in an orthorhombic structure where a=10.56, b=12.43, and c=3.617 belongs to Pnam space group. dc and ac susceptibility and specific-heat measurements show that Pr2BaO4 is paramagnetic down to 2 K, with a vanishing electronic specific-heat coefficient γ. X-ray photoemission spectroscopy shows that Pr is mainly trivalent in Pr2BaO4 and close to being tetravalent in PrBaO3. The pronounced ferromagnetic-like behavior found below 11.7 K in the PrxR1-xBa2Cu3Oz system is due to the impurity of PrBaO3. © 1992 The American Physical Society