Structural, Magnetic, Magnetocaloric, and Magnetostrictive Properties of Pb1-xSrxMnBO4 (x = 0, 0.5, and 1.0)

摘要

x )Sr_(x )MnBO_(4) is reported with an orthorhombic, Pnma , structure throughout; here studies on compounds with x = 0, 0.5, and 1 are described. The structure contains chains of MnO_(6) octahedra that exhibit intra-chain ferromagnetic (FM) order at low temperatures. Neutron powder diffraction (NPD) reveals a dominant FM order in PbMnBO_(4) (T _(c) = 30 K), whereas SrMnBO_(4) is primarily antiferromagnetic (AFM) with T _(N) = 16 K; the difference is related to the link between the chains that involves the BO_(3) groups. PbMnBO_(4) has its moment along a but also has a previously unreported AFM contribution along c (magnetic space group Pnm′a′ ), whereas SrMnBO_(4) has its moment along a but also a FM canting along c (magnetic space group Pn′m′a ). The end members show distinct magnetostriction at T _(c)/T _(N) which correlates with the different magnetic exchange in these compounds. NPD in variable applied magnetic field shows that SrMnBO_(4) is converted to fully FM at 8 T. The behavior above the magnetic ordering temperature is consistent with short-range FM correlations within the chains, which is particularly apparent in PbMnBO_(4). The magnetocaloric effect (MCE) has been measured and compared with those previously reported for the mineral gaudefroyite. PbMnBO_(4) has excellent MCE behavior, especially near T _(c), 30 K. The strong FM exchange within the chains and FM correlations above T _(c) are vital for the MC properties.>