Single Crystal Growth And Magnetic Properties Of Quasi-one-dimensional Spin Chain Ba_xSr_1-xMn₂V₂O₈

The ideal one-dimensional antiferromagnetic spin system does not experience long-range order at finite temperature in theoretical due to the strong quantum spin fluctuations,but slight disturbance of the system due to weak interchain interaction or doping of non-magnetic impurities can make the quantum critical state unstable and tend to form a three-dimensional antiferromagnetic long-range order.For compounds with low spin quantum numbers,the physical properties are strongly influenced by quantum fluctuations,while for high-spin quantum number compounds,it is expected to exhibit more classical behavior.As a low-dimensional magnet,BaMn₂V₂O₈ has a large spin value?S=5/2?,and its magnetic properties may exhibit both classical behavior and quantum behavior.So far,there is controversy about the space group to which BaMn₂V₂O₈ belongs and whether or not there is DM interaction in BaMn₂V₂O₈,and we also don't know its magnetic structure very well.In this paper,Ba_xSr_1-xMn₂V₂O₈ series solid solution single crystals were grown by optical floating zone method.The magnetic properties were systematically studied.We analyzed the changes law of the magnetic properties in the system.The specific results are as follows:?1?By study of the temperature dependent magnetic susceptibility?MT?and magnetic field dependent magnetization?MH?of BaMn₂V₂O₈ single crystal in different directions,it is found that BaMn₂V₂O₈ single crystal is antiferromagnetic below the phase transition temperature,and the magnetization linearly changes with the applied magnetic field.The system does not exist DM interaction.Below the magnetic transition temperature,the magnetic susceptibility along the c-axis increases with decreasing temperature,and the magnetization perpendicular to the c-axis decreases with decreasing temperature,this indicating that the magnetic moment tends to be perpendicular to the c-axis direction,and in the ab plane the magnetic moment tends to be antiparallel arrangement.Based on the above results,we have speculated a possible magnetic structure of BaMn₂V₂O₈ single crystal,in which the spins are arranged anti-parallel to each other in the ab plane,and the adjacent spins are arranged anti-parallel in the c-axis direction to form a spiral chain along the c-axis.?2?The magnetic field dependent magnetization of the SrMn₂V₂O₈ exhibits weak ferromagnetism at low temperatures,and thus is an antiferromagnet with a magnetic moment tilt.When Ba ion in BaMn₂V₂O₈ single crystal is replaced by Sr ion,the magnetic properties of the system are non-monotonous.With the increase of Sr content,the ferromagnetism of the system increases first and then decreases,and the sample of Ba_0.5Sr_0.5Mn₂V₂O₈ single crystal has the strongest weak ferromagnetism.It is found by the high-temperature magnetic susceptibility fitting that the nearest neighbor antiferromagnetic interchain interaction shows a first decrease and then increase with the increase of Sr content.The nearest neighbor antiferromagnetic interaction of Ba_0.5Sr_0.5Mn₂V₂O₈ is the weakest,so it shows strong ferromagnetism and high magnetic transition temperature.?3?The strength of the nearest neighbor interaction is closely related to the distance between adjacent spins and the overlap of electron clouds between them.The closer the distance,the stronger the interaction;the less the electron cloud overlaps,the weaker the interaction.As the Sr content increases,the distance between adjacent spins becomes smaller and smaller,but the complete anti-parallel between the magnetic moments is destroyed,and the occurrence of the angle of the magnetic moment causes the electron cloud overlap to become smaller,so the interaction between the spins has a non-monotonic change.