000208642 001__ 208642
000208642 005__ 20190317000201.0
000208642 0247_ $$2doi$$a10.1103/PhysRevB.91.024407
000208642 022__ $$a1098-0121
000208642 02470 $$2ISI$$a000349126900002
000208642 037__ $$aARTICLE
000208642 245__ $$aCompeting Jahn-Teller distortions and ferrimagnetic ordering in the geometrically frustrated system Ni1-xCuxCr2O4
000208642 260__ $$bAmer Physical Soc$$c2015$$aCollege Pk
000208642 269__ $$a2015
000208642 300__ $$a12
000208642 336__ $$aJournal Articles
000208642 520__ $$aCompeting Jahn-Teller distortions combined with geometrical frustration give rise to a rich phase diagram as a function of x(Cu) and temperature in the spinel system Ni1-xCuxCr2O4. The Jahn-Teller distortion of the end members acts in opposite ways, with an elongation of the NiO4 tetrahedra resulting in a structural transition at T-S1 = 317K in NiCr2O4, but a flattening in the CuO4 tetrahedra at T-S1 = 846K in CuCr2O4. In both cases the symmetry is lowered from cubic (Fd (3) over barm) to tetragonal (I4(1)/amd) on cooling. In order to follow the influence of Jahn-Teller active Ni2+ and Cu2+ ions on the structural and magnetic properties of chromium spinels, we have investigated a series of samples of Ni1-xCuxCr2O4 by x-ray and neutron powder diffraction. In the critical range 0.10 < x(Cu) < 0.20, strong orthorhombic distortions were observed, where competing Jahn-Teller activities between the Cu2+ and Ni2+ ions result in distortions along both the a and c axes. For Ni0.85Cu0.15Cr2O4, the orthorhombic structure (Fddd) is stabilized up to T-S2 = 368(2) K, close to the first structural phase transition at T-S1 = 374(2) K. A ferrimagnetic spin alignment of the Ni/Cu and chromium atoms sets in at much lower temperature TC = 95K in this compound. The end members NiCr2O4 and CuCr2O4 undergo this ferrimagnetic transition at TC = 74 and 135 K, respectively. These transitions are accompanied by the structural change to the orthorhombic symmetry which relieves the frustration. NiCr2O4 and Ni0.85Cu0.15Cr2O4 undergo a second magnetic transition at TM2 = 24 and 67K due to a superimposed antiferromagnetic ordering of the Cr moments resulting in a noncollinear magnetic structure. In the system Ni1-xCuxCr2O4, the magnetic transitions TC and TM2 merge with increasing copper content up to x(Cu) similar to 0.5. For the Ni-rich chromites, geometrical frustration causes a strong reduction of the chromium moments, where magnetic long-range order coexists with a disordered spin-liquid-like or a reentrant-spin-glass-like state. This paper provides insight into the interplay between the Jahn-Teller effect, geometrical frustration, and long-range magnetic order in these complex systems.
000208642 700__ $$uHelmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany$$aReehuis, M.
000208642 700__ $$uHelmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany$$aTovar, M.
000208642 700__ $$uHelmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany$$aToebbens, D. M.
000208642 700__ $$0240470$$g168557$$uESRF, Swiss Norwegian Beamline SNBL, F-38042 Grenoble 9, France$$aPattison, P.
000208642 700__ $$uHelmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany$$aHoser, A.
000208642 700__ $$aLake, B.$$uHelmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany
000208642 773__ $$j91$$tPhysical Review B$$k2
000208642 8564_ $$uhttp://lqm.epfl.ch/$$zURL
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000208642 937__ $$aEPFL-ARTICLE-208642
000208642 973__ $$rREVIEWED$$sPUBLISHED$$aEPFL
000208642 980__ $$aARTICLE