The ability to control magnetic and electric properties is attractive for tailoring materials for devices, data storage and sensor technology. In magnetoelectric materials, these two degrees of freedom are closely linked and this makes them particularly interesting [1]. Here we study one such system, LiNi(1-x)FexPO4, using magnetometry, polarized neutron diffraction, pyrocurrent measurements and Monte Carlo simulations. The parent compounds of this mixed system, LiNiPO4 and LiFePO4, possess mismatched magnetic anisotropies [2-6] and here we demonstrate that by random magnetic anisotropy mixing it is possible to tune the magnetic and magnetoelectric properties [7]. Interestingly, the ordered moment in the ground state is rotated with respect to the plane spanned by the easy axes of the parent compounds. Such behavior was previously theoretically predicted [8] and our study provides the first clear experimental evidence for such phase. Most remarkably, as a consequence of the lower magnetic symmetry, additional magnetoelectric couplings are unlocked and enhanced in the system. Our study shows that mixed-anisotropy magnetoelectric antiferromagnets represent a promising route with general applicability towards control of magnetoelectric properties, relying only on chemical disorder.
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