Nonmonotonic aftereffect measurements in perpendicular synthetic ferrimagnets

Abstract

Aftereffect measurements have been performed on synthetic ferrimagnets showing strong perpendicular magnetic anisotropy, namely (Co/Pt)/Ir/(Co/Pt), by measuring the magnetization of the sample as a function of time for several different applied magnetic fields. Unexpected magnetic relaxation has been observed. Indeed, for some particular applied magnetic fields, the magnetization as a function of time first plummets and then increases. This nonmonotonic aftereffect can be understood by considering the possible magnetic states and the transitions between those states. This understanding has been confirmed and detailed using magneto-optical Kerr effect (MOKE) microscopy. Indeed, the measurements show nucleation and propagation of a transient metastable magnetic configuration. Furthermore, we were able to obtain a good qualitative agreement between a simple one-dimensional model and the experimental observation. We could strongly support the hypothesis that this peculiar nonmonotonic behavior could be a very general feature that should be observed in any antiferromagnetically coupled system (synthetic ferrimagnets, synthetic antiferromagnets) with perpendicular magnetic anisotropy.

Генерация неравновесных зародышей намагниченности в быстро нарастающем магнитном поле в синтетических ферримагнетиках Pt/Co/Ir/Co/Pt

“…Si/SiO 2 /Pt(3.2 nm)/ Co(1.1 nm)/Ir(1.4 nm)/Co(0.8 nm)/Pt(3.2 nm) размером 4 × 4 mm 2 была выращена методом магнетронного напыления при T = 300 K. Способ приготовления и аттестация образца представлены в [7,12].…”

“…Возникновение неравновесного промежуточного состояния намагниченности в постоянном магнитном поле мы наблюдали в образцах всей серии Pt/Co/Ir/Co(t Co )/Pt, где t Co -толщина верхнего слоя Co (t Co = 0.6 nm, 0.7 nm, 0.8 nm, 1.0 nm) [7,8]. Обсуждаемый в настоящей статье образец с t Co = 0.8 nm проявлял длительную немонотонную релаксацию при T = 170 K [8], из-за совпадения двух полей переходов между тремя стабильными состояниями намагниченности.…”

“…Энергия межслойного обмена и его тип (ферромагнитный или антиферромагнитный) имеют осциллирующую зависимость от толщины спейсера [6]. Перемагничивание синтетического ферримагнетика может протекать немонотонно в постоянном магнитном поле [7,8] с образованием неравновесной фазы намагниченности, а тип магнитной релаксации (монотонный или немонотонный) управляется полями переключения [9]. Процесс перемагничивания является термоактивационным и кроме температуры управляется толщиной ферромагнитных слоев и скоростью развертки магнитного поля [10].…”

A low-temperature Kerr effect microscope for the simultaneous magneto-optic and magneto-transport study of magnetic topological insulators

“…Single-pass hysteresis loops of 30-nm-wide Co nanowires have been successfully detected by MOKE magnetometry [6], demonstrating a measurement sensitivity comparable to that of the latest SQUID magnetometers (10 −12 to 10 −13 Am 2 ). Utilising the spatial resolving power, MOKE microscopy has also been used to resolve the spin Hall effect in metals and semiconductors [7][8][9], to map spin injection and drift in ferromagnet/semiconductor heterostructures [10,11], to verify ferromagnetism in two-dimensional van der Waals crystals [12,13], and to trace non-monotonic spin relaxation in perpendicular synthetic ferrimagnets [14].…”

Influence of the magnetic field sweeping rate on magnetic transitions in synthetic ferrimagnets with perpendicular anisotropy

“…Thus, the values of magnetization reversal parameters in nanosized heterostructures as nanopillars and nanodots are independent of the measurement technique used. In contrast, heterostructures of a large lateral size (5 mm  5 mm or larger) manifest long-lasting magnetic relaxation dynamics ($10 3 -10 4 s), limited by the domain propagation time throughout the sample area, 9,10 and the duration of magnetization reversal can become comparable to the magnetic hysteresis loop recording time. In that case, the observed value of the interstate transition field is expected to be strongly dependent on MFSR.…”